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000
FXUS63 KLOT 180809
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
209 AM CST THU DEC 18 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CIGS THIS MORNING. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS CONTINUE TO SLOWLY ERODE FROM THE NORTH WHILE REMAINING
STEADY TO THE SOUTHWEST...RPJ/C09/IKK. CONFIDENCE REGARDING TRENDS
IS LOW BUT IF THEY CONTINUE...WILL LIKELY SEE SOME SCATTERING OF
LOW CLOUDS FROM THE NORTH OVERNIGHT...WITH CLEARING AT GYY/MDW
LIKELY TO BE LATER THIS MORNING. NORTHWEST WINDS 4-8KTS WILL
LIKELY BECOME LIGHT AND VRB WHERE CLOUDS CLEAR...WITH LIGHT
NORTHWEST WINDS THRU THE DAY AND BECOMING LIGHT AND VRB TONIGHT.
CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY AND SATURDAY...DRY WITH VFR LIKELY...THOUGH MVFR POSSIBLE.
LIGHT AND VARIABLE WINDS.

SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.

MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS...POSSIBLY
TURNING SOUTHEAST.

TUESDAY...CHANCE OF RAIN MIXED WITH SNOW. IFR POSSIBLE. SOUTHWEST
WINDS.

KMD

&&

.MARINE...

209 AM...A LARGE AREA OF HIGH PRESSURE EXTENDING FROM ONTARIO
SOUTH TO ILLINOIS WILL VERY SLOWLY MOVE EAST ACROSS THE GREAT
LAKES TODAY AND FRIDAY...THEN ACROSS THE EASTERN LAKES AND INTO
QUEBEC SATURDAY AND SUNDAY. NORTHWESTERLY WINDS WILL GRADUALLY
DIMINISH TODAY...WITH A 36-48 HOUR PERIOD OF LIGHT WINDS...5-10
KTS...EXPECTED AS THE HIGH MOVES EAST. WINDS WILL SHIFT SOUTHERLY
SATURDAY ON THE BACK SIDE OF THE HIGH BUT STILL REMAIN LIGHT. THE
SOUTHERLY WINDS WILL BEGIN TO INCREASE SUNDAY AS THE GRADIENT
BEGINS TO TIGHTEN AHEAD OF DEVELOPING LOW PRESSURE IN THE PLAINS.
THIS LOW WILL TRACK NORTHEAST TOWARD THE WESTERN LAKES REGION BY
EARLY/MID NEXT WEEK...BUT STILL QUITE A BIT OF UNCERTAINTY
REGARDING ITS TRACK/STRENGTHEN/TIMING. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 180809
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
209 AM CST THU DEC 18 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CIGS THIS MORNING. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS CONTINUE TO SLOWLY ERODE FROM THE NORTH WHILE REMAINING
STEADY TO THE SOUTHWEST...RPJ/C09/IKK. CONFIDENCE REGARDING TRENDS
IS LOW BUT IF THEY CONTINUE...WILL LIKELY SEE SOME SCATTERING OF
LOW CLOUDS FROM THE NORTH OVERNIGHT...WITH CLEARING AT GYY/MDW
LIKELY TO BE LATER THIS MORNING. NORTHWEST WINDS 4-8KTS WILL
LIKELY BECOME LIGHT AND VRB WHERE CLOUDS CLEAR...WITH LIGHT
NORTHWEST WINDS THRU THE DAY AND BECOMING LIGHT AND VRB TONIGHT.
CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY AND SATURDAY...DRY WITH VFR LIKELY...THOUGH MVFR POSSIBLE.
LIGHT AND VARIABLE WINDS.

SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.

MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS...POSSIBLY
TURNING SOUTHEAST.

TUESDAY...CHANCE OF RAIN MIXED WITH SNOW. IFR POSSIBLE. SOUTHWEST
WINDS.

KMD

&&

.MARINE...

209 AM...A LARGE AREA OF HIGH PRESSURE EXTENDING FROM ONTARIO
SOUTH TO ILLINOIS WILL VERY SLOWLY MOVE EAST ACROSS THE GREAT
LAKES TODAY AND FRIDAY...THEN ACROSS THE EASTERN LAKES AND INTO
QUEBEC SATURDAY AND SUNDAY. NORTHWESTERLY WINDS WILL GRADUALLY
DIMINISH TODAY...WITH A 36-48 HOUR PERIOD OF LIGHT WINDS...5-10
KTS...EXPECTED AS THE HIGH MOVES EAST. WINDS WILL SHIFT SOUTHERLY
SATURDAY ON THE BACK SIDE OF THE HIGH BUT STILL REMAIN LIGHT. THE
SOUTHERLY WINDS WILL BEGIN TO INCREASE SUNDAY AS THE GRADIENT
BEGINS TO TIGHTEN AHEAD OF DEVELOPING LOW PRESSURE IN THE PLAINS.
THIS LOW WILL TRACK NORTHEAST TOWARD THE WESTERN LAKES REGION BY
EARLY/MID NEXT WEEK...BUT STILL QUITE A BIT OF UNCERTAINTY
REGARDING ITS TRACK/STRENGTHEN/TIMING. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 180809
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
209 AM CST THU DEC 18 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CIGS THIS MORNING. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS CONTINUE TO SLOWLY ERODE FROM THE NORTH WHILE REMAINING
STEADY TO THE SOUTHWEST...RPJ/C09/IKK. CONFIDENCE REGARDING TRENDS
IS LOW BUT IF THEY CONTINUE...WILL LIKELY SEE SOME SCATTERING OF
LOW CLOUDS FROM THE NORTH OVERNIGHT...WITH CLEARING AT GYY/MDW
LIKELY TO BE LATER THIS MORNING. NORTHWEST WINDS 4-8KTS WILL
LIKELY BECOME LIGHT AND VRB WHERE CLOUDS CLEAR...WITH LIGHT
NORTHWEST WINDS THRU THE DAY AND BECOMING LIGHT AND VRB TONIGHT.
CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY AND SATURDAY...DRY WITH VFR LIKELY...THOUGH MVFR POSSIBLE.
LIGHT AND VARIABLE WINDS.

SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.

MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS...POSSIBLY
TURNING SOUTHEAST.

TUESDAY...CHANCE OF RAIN MIXED WITH SNOW. IFR POSSIBLE. SOUTHWEST
WINDS.

KMD

&&

.MARINE...

209 AM...A LARGE AREA OF HIGH PRESSURE EXTENDING FROM ONTARIO
SOUTH TO ILLINOIS WILL VERY SLOWLY MOVE EAST ACROSS THE GREAT
LAKES TODAY AND FRIDAY...THEN ACROSS THE EASTERN LAKES AND INTO
QUEBEC SATURDAY AND SUNDAY. NORTHWESTERLY WINDS WILL GRADUALLY
DIMINISH TODAY...WITH A 36-48 HOUR PERIOD OF LIGHT WINDS...5-10
KTS...EXPECTED AS THE HIGH MOVES EAST. WINDS WILL SHIFT SOUTHERLY
SATURDAY ON THE BACK SIDE OF THE HIGH BUT STILL REMAIN LIGHT. THE
SOUTHERLY WINDS WILL BEGIN TO INCREASE SUNDAY AS THE GRADIENT
BEGINS TO TIGHTEN AHEAD OF DEVELOPING LOW PRESSURE IN THE PLAINS.
THIS LOW WILL TRACK NORTHEAST TOWARD THE WESTERN LAKES REGION BY
EARLY/MID NEXT WEEK...BUT STILL QUITE A BIT OF UNCERTAINTY
REGARDING ITS TRACK/STRENGTHEN/TIMING. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 180809
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
209 AM CST THU DEC 18 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CIGS THIS MORNING. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS CONTINUE TO SLOWLY ERODE FROM THE NORTH WHILE REMAINING
STEADY TO THE SOUTHWEST...RPJ/C09/IKK. CONFIDENCE REGARDING TRENDS
IS LOW BUT IF THEY CONTINUE...WILL LIKELY SEE SOME SCATTERING OF
LOW CLOUDS FROM THE NORTH OVERNIGHT...WITH CLEARING AT GYY/MDW
LIKELY TO BE LATER THIS MORNING. NORTHWEST WINDS 4-8KTS WILL
LIKELY BECOME LIGHT AND VRB WHERE CLOUDS CLEAR...WITH LIGHT
NORTHWEST WINDS THRU THE DAY AND BECOMING LIGHT AND VRB TONIGHT.
CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY AND SATURDAY...DRY WITH VFR LIKELY...THOUGH MVFR POSSIBLE.
LIGHT AND VARIABLE WINDS.

SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.

MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS...POSSIBLY
TURNING SOUTHEAST.

TUESDAY...CHANCE OF RAIN MIXED WITH SNOW. IFR POSSIBLE. SOUTHWEST
WINDS.

KMD

&&

.MARINE...

209 AM...A LARGE AREA OF HIGH PRESSURE EXTENDING FROM ONTARIO
SOUTH TO ILLINOIS WILL VERY SLOWLY MOVE EAST ACROSS THE GREAT
LAKES TODAY AND FRIDAY...THEN ACROSS THE EASTERN LAKES AND INTO
QUEBEC SATURDAY AND SUNDAY. NORTHWESTERLY WINDS WILL GRADUALLY
DIMINISH TODAY...WITH A 36-48 HOUR PERIOD OF LIGHT WINDS...5-10
KTS...EXPECTED AS THE HIGH MOVES EAST. WINDS WILL SHIFT SOUTHERLY
SATURDAY ON THE BACK SIDE OF THE HIGH BUT STILL REMAIN LIGHT. THE
SOUTHERLY WINDS WILL BEGIN TO INCREASE SUNDAY AS THE GRADIENT
BEGINS TO TIGHTEN AHEAD OF DEVELOPING LOW PRESSURE IN THE PLAINS.
THIS LOW WILL TRACK NORTHEAST TOWARD THE WESTERN LAKES REGION BY
EARLY/MID NEXT WEEK...BUT STILL QUITE A BIT OF UNCERTAINTY
REGARDING ITS TRACK/STRENGTHEN/TIMING. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 180605
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1205 AM CST THU DEC 18 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CIGS THIS MORNING. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS CONTINUE TO SLOWLY ERODE FROM THE NORTH WHILE REMAINING
STEADY TO THE SOUTHWEST...RPJ/C09/IKK. CONFIDENCE REGARDING TRENDS
IS LOW BUT IF THEY CONTINUE...WILL LIKELY SEE SOME SCATTERING OF
LOW CLOUDS FROM THE NORTH OVERNIGHT...WITH CLEARING AT GYY/MDW
LIKELY TO BE LATER THIS MORNING. NORTHWEST WINDS 4-8KTS WILL
LIKELY BECOME LIGHT AND VRB WHERE CLOUDS CLEAR...WITH LIGHT
NORTHWEST WINDS THRU THE DAY AND BECOMING LIGHT AND VRB TONIGHT.
CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY AND SATURDAY...DRY WITH VFR LIKELY...THOUGH MVFR POSSIBLE.
LIGHT AND VARIABLE WINDS.

SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.

MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS...POSSIBLY
TURNING SOUTHEAST.

TUESDAY...CHANCE OF RAIN MIXED WITH SNOW. IFR POSSIBLE. SOUTHWEST
WINDS.

KMD

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL
     10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 180605
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1205 AM CST THU DEC 18 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CIGS THIS MORNING. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS CONTINUE TO SLOWLY ERODE FROM THE NORTH WHILE REMAINING
STEADY TO THE SOUTHWEST...RPJ/C09/IKK. CONFIDENCE REGARDING TRENDS
IS LOW BUT IF THEY CONTINUE...WILL LIKELY SEE SOME SCATTERING OF
LOW CLOUDS FROM THE NORTH OVERNIGHT...WITH CLEARING AT GYY/MDW
LIKELY TO BE LATER THIS MORNING. NORTHWEST WINDS 4-8KTS WILL
LIKELY BECOME LIGHT AND VRB WHERE CLOUDS CLEAR...WITH LIGHT
NORTHWEST WINDS THRU THE DAY AND BECOMING LIGHT AND VRB TONIGHT.
CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY AND SATURDAY...DRY WITH VFR LIKELY...THOUGH MVFR POSSIBLE.
LIGHT AND VARIABLE WINDS.

SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.

MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS...POSSIBLY
TURNING SOUTHEAST.

TUESDAY...CHANCE OF RAIN MIXED WITH SNOW. IFR POSSIBLE. SOUTHWEST
WINDS.

KMD

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL
     10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 180304
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
904 PM CST WED DEC 17 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* MVFR CEILINGS TONIGHT AND POSSIBLY FOR A TIME TOMORROW

KMD

//DISCUSSION...UPDATED 00Z...

MVFR CLOUD DECK AROUND 2000-2500 FT IS SHOWING SIGNS OF CLEARING
IN SW WI. GUIDANCE IS MIXED ON WHEN IT WILL SCATTER OUT...WITH
MUCH OF THS MOS GUIDANCE SUGGESTING IT WILL DO SO AROUND 4Z. THE
RUC IS HANGING ONTO CLOUDS THROUGH ABOUT 8Z. WILL HOLD THE
PESSIMISTIC ROUTE FOR NOW TO SEE HOW THE CLOUDS CONTINUE CLEARING
AFTER SUNSET.

OTHERWISE GUIDANCE REMAINS MIXED AS TO WHETHER LOWER CLOUDS WILL
RETURN FROM THE WAVE DROPPING SOUTH THROUGH N WI. FEELING IS THAT
THESE CLOUDS WILL NOT MAKE IT DOWN AT THIS POINT AS WE GET MORE
WESTERLY FLOW PUSHING ALOFT BUT THIS WILL BEAR WATCHING.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM-HIGH THAT MVFR WILL SCATTER OVERNIGHT BUT MEDIUM-LOW ON
  TIMING AND ON IF IT WILL RETURN TOMORROW

KMD

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY AND SATURDAY...DRY WITH VFR LIKELY...THOUGH MVFR POSSIBLE. LIGHT AND
VARIABLE WINDS.

SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.

MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS...POSSIBLY
TURNING SOUTHEAST.

TUESDAY...CHANCE OF RAIN MIXED WITH SNOW. IFR POSSIBLE. SOUTHWEST
WINDS.

KMD

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 180304
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
904 PM CST WED DEC 17 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* MVFR CEILINGS TONIGHT AND POSSIBLY FOR A TIME TOMORROW

KMD

//DISCUSSION...UPDATED 00Z...

MVFR CLOUD DECK AROUND 2000-2500 FT IS SHOWING SIGNS OF CLEARING
IN SW WI. GUIDANCE IS MIXED ON WHEN IT WILL SCATTER OUT...WITH
MUCH OF THS MOS GUIDANCE SUGGESTING IT WILL DO SO AROUND 4Z. THE
RUC IS HANGING ONTO CLOUDS THROUGH ABOUT 8Z. WILL HOLD THE
PESSIMISTIC ROUTE FOR NOW TO SEE HOW THE CLOUDS CONTINUE CLEARING
AFTER SUNSET.

OTHERWISE GUIDANCE REMAINS MIXED AS TO WHETHER LOWER CLOUDS WILL
RETURN FROM THE WAVE DROPPING SOUTH THROUGH N WI. FEELING IS THAT
THESE CLOUDS WILL NOT MAKE IT DOWN AT THIS POINT AS WE GET MORE
WESTERLY FLOW PUSHING ALOFT BUT THIS WILL BEAR WATCHING.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM-HIGH THAT MVFR WILL SCATTER OVERNIGHT BUT MEDIUM-LOW ON
  TIMING AND ON IF IT WILL RETURN TOMORROW

KMD

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY AND SATURDAY...DRY WITH VFR LIKELY...THOUGH MVFR POSSIBLE. LIGHT AND
VARIABLE WINDS.

SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.

MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS...POSSIBLY
TURNING SOUTHEAST.

TUESDAY...CHANCE OF RAIN MIXED WITH SNOW. IFR POSSIBLE. SOUTHWEST
WINDS.

KMD

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 172356
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
556 PM CST WED DEC 17 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* MVFR CEILINGS TONIGHT AND POSSIBLY FOR A TIME TOMORROW

KMD

//DISCUSSION...UPDATED 00Z...

MVFR CLOUD DECK AROUND 2000-2500 FT IS SHOWING SIGNS OF CLEARING
IN SW WI. GUIDANCE IS MIXED ON WHEN IT WILL SCATTER OUT...WITH
MUCH OF THS MOS GUIDANCE SUGGESTING IT WILL DO SO AROUND 4Z. THE
RUC IS HANGING ONTO CLOUDS THROUGH ABOUT 8Z. WILL HOLD THE
PESSIMISTIC ROUTE FOR NOW TO SEE HOW THE CLOUDS CONTINUE CLEARING
AFTER SUNSET.

OTHERWISE GUIDANCE REMAINS MIXED AS TO WHETHER LOWER CLOUDS WILL
RETURN FROM THE WAVE DROPPING SOUTH THROUGH N WI. FEELING IS THAT
THESE CLOUDS WILL NOT MAKE IT DOWN AT THIS POINT AS WE GET MORE
WESTERLY FLOW PUSHING ALOFT BUT THIS WILL BEAR WATCHING.

KMD


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH THAT MVFR WILL CLEAR OVERNIGHT BUT LOW ON TIMING AND ON IF
  IT WILL RETURN TOMORROW

KMD

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY AND SATURDAY...DRY WITH VFR LIKELY...THOUGH MVFR POSSIBLE. LIGHT AND
VARIABLE WINDS.

SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.

MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS...POSSIBLY
TURNING SOUTHEAST.

TUESDAY...CHANCE OF RAIN MIXED WITH SNOW. IFR POSSIBLE. SOUTHWEST
WINDS.

KMD

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 172356
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
556 PM CST WED DEC 17 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* MVFR CEILINGS TONIGHT AND POSSIBLY FOR A TIME TOMORROW

KMD

//DISCUSSION...UPDATED 00Z...

MVFR CLOUD DECK AROUND 2000-2500 FT IS SHOWING SIGNS OF CLEARING
IN SW WI. GUIDANCE IS MIXED ON WHEN IT WILL SCATTER OUT...WITH
MUCH OF THS MOS GUIDANCE SUGGESTING IT WILL DO SO AROUND 4Z. THE
RUC IS HANGING ONTO CLOUDS THROUGH ABOUT 8Z. WILL HOLD THE
PESSIMISTIC ROUTE FOR NOW TO SEE HOW THE CLOUDS CONTINUE CLEARING
AFTER SUNSET.

OTHERWISE GUIDANCE REMAINS MIXED AS TO WHETHER LOWER CLOUDS WILL
RETURN FROM THE WAVE DROPPING SOUTH THROUGH N WI. FEELING IS THAT
THESE CLOUDS WILL NOT MAKE IT DOWN AT THIS POINT AS WE GET MORE
WESTERLY FLOW PUSHING ALOFT BUT THIS WILL BEAR WATCHING.

KMD


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH THAT MVFR WILL CLEAR OVERNIGHT BUT LOW ON TIMING AND ON IF
  IT WILL RETURN TOMORROW

KMD

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY AND SATURDAY...DRY WITH VFR LIKELY...THOUGH MVFR POSSIBLE. LIGHT AND
VARIABLE WINDS.

SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.

MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS...POSSIBLY
TURNING SOUTHEAST.

TUESDAY...CHANCE OF RAIN MIXED WITH SNOW. IFR POSSIBLE. SOUTHWEST
WINDS.

KMD

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 172215
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
415 PM CST WED DEC 17 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* MVFR CEILING TRENDS AND POSSIBLE SCATTERING.

* WIND TRENDS...GUSTINESS TODAY AND VARIABLE LATE TONIGHT.

LENNING

//DISCUSSION...UPDATED 18Z...

CEILINGS ARE HANGING IN THE MVFR RANGE BUT SHOWING SIGNS OF
SCATTERING OUT IN AREAS WEST OF THE ORD/MDW TERMINALS. GIVEN THE
PERSISTENCE OF THIS CLOUD SHIELD IT IS HARD TO PUSH THE CLEARING
INTO THE AREA BEFORE WE ACTUALLY SEE IT HAPPENING...SO FOR NOW
WILL MAINTAIN CURRENT TRENDS INTO THE OVERNIGHT HOURS. WINDS
REMAIN WESTERLY TO NORTHWESTERLY FOR MOST OF THE PERIOD...BUT BY
TOMORROW A WEAKENING PRESSURE GRADIENT MAY ALLOW WINDS TO GO
VARIABLE FOR A TIME...THOUGH LIKELY CONTINUE TO FAVOR A WESTERLY
COMPONENT.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* HIGHER CONFIDENCE IN WIND TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 172215
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
415 PM CST WED DEC 17 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* MVFR CEILING TRENDS AND POSSIBLE SCATTERING.

* WIND TRENDS...GUSTINESS TODAY AND VARIABLE LATE TONIGHT.

LENNING

//DISCUSSION...UPDATED 18Z...

CEILINGS ARE HANGING IN THE MVFR RANGE BUT SHOWING SIGNS OF
SCATTERING OUT IN AREAS WEST OF THE ORD/MDW TERMINALS. GIVEN THE
PERSISTENCE OF THIS CLOUD SHIELD IT IS HARD TO PUSH THE CLEARING
INTO THE AREA BEFORE WE ACTUALLY SEE IT HAPPENING...SO FOR NOW
WILL MAINTAIN CURRENT TRENDS INTO THE OVERNIGHT HOURS. WINDS
REMAIN WESTERLY TO NORTHWESTERLY FOR MOST OF THE PERIOD...BUT BY
TOMORROW A WEAKENING PRESSURE GRADIENT MAY ALLOW WINDS TO GO
VARIABLE FOR A TIME...THOUGH LIKELY CONTINUE TO FAVOR A WESTERLY
COMPONENT.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* HIGHER CONFIDENCE IN WIND TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 172033
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
233 PM CST WED DEC 17 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* MVFR CEILING TRENDS AND POSSIBLE SCATTERING.

* WIND TRENDS...GUSTINESS TODAY AND VARIABLE LATE TONIGHT.

LENNING

//DISCUSSION...UPDATED 18Z...

CEILINGS ARE HANGING IN THE MVFR RANGE BUT SHOWING SIGNS OF
SCATTERING OUT IN AREAS WEST OF THE ORD/MDW TERMINALS. GIVEN THE
PERSISTENCE OF THIS CLOUD SHIELD IT IS HARD TO PUSH THE CLEARING
INTO THE AREA BEFORE WE ACTUALLY SEE IT HAPPENING...SO FOR NOW
WILL MAINTAIN CURRENT TRENDS INTO THE OVERNIGHT HOURS. WINDS
REMAIN WESTERLY TO NORTHWESTERLY FOR MOST OF THE PERIOD...BUT BY
TOMORROW A WEAKENING PRESSURE GRADIENT MAY ALLOW WINDS TO GO
VARIABLE FOR A TIME...THOUGH LIKELY CONTINUE TO FAVOR A WESTERLY
COMPONENT.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* HIGHER CONFIDENCE IN WIND TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 172010
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
210 PM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* MVFR CEILING TRENDS AND POSSIBLE SCATTERING.

* WIND TRENDS...GUSTINESS TODAY AND VARIABLE LATE TONIGHT.

LENNING

//DISCUSSION...UPDATED 18Z...

CEILINGS ARE HANGING IN THE MVFR RANGE BUT SHOWING SIGNS OF
SCATTERING OUT IN AREAS WEST OF THE ORD/MDW TERMINALS. GIVEN THE
PERSISTENCE OF THIS CLOUD SHIELD IT IS HARD TO PUSH THE CLEARING
INTO THE AREA BEFORE WE ACTUALLY SEE IT HAPPENING...SO FOR NOW
WILL MAINTAIN CURRENT TRENDS INTO THE OVERNIGHT HOURS. WINDS
REMAIN WESTERLY TO NORTHWESTERLY FOR MOST OF THE PERIOD...BUT BY
TOMORROW A WEAKENING PRESSURE GRADIENT MAY ALLOW WINDS TO GO
VARIABLE FOR A TIME...THOUGH LIKELY CONTINUE TO FAVOR A WESTERLY
COMPONENT.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* HIGHER CONFIDENCE IN WIND TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 172010
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
210 PM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* MVFR CEILING TRENDS AND POSSIBLE SCATTERING.

* WIND TRENDS...GUSTINESS TODAY AND VARIABLE LATE TONIGHT.

LENNING

//DISCUSSION...UPDATED 18Z...

CEILINGS ARE HANGING IN THE MVFR RANGE BUT SHOWING SIGNS OF
SCATTERING OUT IN AREAS WEST OF THE ORD/MDW TERMINALS. GIVEN THE
PERSISTENCE OF THIS CLOUD SHIELD IT IS HARD TO PUSH THE CLEARING
INTO THE AREA BEFORE WE ACTUALLY SEE IT HAPPENING...SO FOR NOW
WILL MAINTAIN CURRENT TRENDS INTO THE OVERNIGHT HOURS. WINDS
REMAIN WESTERLY TO NORTHWESTERLY FOR MOST OF THE PERIOD...BUT BY
TOMORROW A WEAKENING PRESSURE GRADIENT MAY ALLOW WINDS TO GO
VARIABLE FOR A TIME...THOUGH LIKELY CONTINUE TO FAVOR A WESTERLY
COMPONENT.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* HIGHER CONFIDENCE IN WIND TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 171953
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
153 PM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* MVFR CEILING TRENDS AND POSSIBLE SCATTERING.

* WIND TRENDS...GUSTINESS TODAY AND VARIABLE LATE TONIGHT.

LENNING

//DISCUSSION...UPDATED 18Z...

CEILINGS ARE HANGING IN THE MVFR RANGE BUT SHOWING SIGNS OF
SCATTERING OUT IN AREAS WEST OF THE ORD/MDW TERMINALS. GIVEN THE
PERSISTENCE OF THIS CLOUD SHIELD IT IS HARD TO PUSH THE CLEARING
INTO THE AREA BEFORE WE ACTUALLY SEE IT HAPPENING...SO FOR NOW
WILL MAINTAIN CURRENT TRENDS INTO THE OVERNIGHT HOURS. WINDS
REMAIN WESTERLY TO NORTHWESTERLY FOR MOST OF THE PERIOD...BUT BY
TOMORROW A WEAKENING PRESSURE GRADIENT MAY ALLOW WINDS TO GO
VARIABLE FOR A TIME...THOUGH LIKELY CONTINUE TO FAVOR A WESTERLY
COMPONENT.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* HIGHER CONFIDENCE IN WIND TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 171953
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
153 PM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* MVFR CEILING TRENDS AND POSSIBLE SCATTERING.

* WIND TRENDS...GUSTINESS TODAY AND VARIABLE LATE TONIGHT.

LENNING

//DISCUSSION...UPDATED 18Z...

CEILINGS ARE HANGING IN THE MVFR RANGE BUT SHOWING SIGNS OF
SCATTERING OUT IN AREAS WEST OF THE ORD/MDW TERMINALS. GIVEN THE
PERSISTENCE OF THIS CLOUD SHIELD IT IS HARD TO PUSH THE CLEARING
INTO THE AREA BEFORE WE ACTUALLY SEE IT HAPPENING...SO FOR NOW
WILL MAINTAIN CURRENT TRENDS INTO THE OVERNIGHT HOURS. WINDS
REMAIN WESTERLY TO NORTHWESTERLY FOR MOST OF THE PERIOD...BUT BY
TOMORROW A WEAKENING PRESSURE GRADIENT MAY ALLOW WINDS TO GO
VARIABLE FOR A TIME...THOUGH LIKELY CONTINUE TO FAVOR A WESTERLY
COMPONENT.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* HIGHER CONFIDENCE IN WIND TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 171812
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1212 PM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* MVFR CEILING TRENDS AND POSSIBLE SCATTERING.

* WIND TRENDS...GUSTINESS TODAY AND VARIABLE LATE TONIGHT.

LENNING

//DISCUSSION...UPDATED 18Z...

CEILINGS ARE HANGING IN THE MVFR RANGE BUT SHOWING SIGNS OF
SCATTERING OUT IN AREAS WEST OF THE ORD/MDW TERMINALS. GIVEN THE
PERSISTENCE OF THIS COULD SHIELD IT IS HARD TO PUSH THE CLEARING
INTO THE AREA BEFORE WE ACTUALLY SEE IT HAPPENING...SO FOR NOW WILL
MAINTAIN CURRENT TRENDS INTO THE OVERNIGHT HOURS. WINDS REMAIN
WESTERLY TO NORTHWESTERLY FOR MOST OF THE PERIOD...BUT BY TOMORROW
A WEAKENING PRESSURE GRADIENT MAY ALLOW WINDS TO GO VARIABLE FOR A
TIME...BUT LIKELY CONTINUE TO FAVOR A WESTERLY COMPONENT.

LENNING


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* HIGHER CONFIDENCE IN WIND TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 171812
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1212 PM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* MVFR CEILING TRENDS AND POSSIBLE SCATTERING.

* WIND TRENDS...GUSTINESS TODAY AND VARIABLE LATE TONIGHT.

LENNING

//DISCUSSION...UPDATED 18Z...

CEILINGS ARE HANGING IN THE MVFR RANGE BUT SHOWING SIGNS OF
SCATTERING OUT IN AREAS WEST OF THE ORD/MDW TERMINALS. GIVEN THE
PERSISTENCE OF THIS COULD SHIELD IT IS HARD TO PUSH THE CLEARING
INTO THE AREA BEFORE WE ACTUALLY SEE IT HAPPENING...SO FOR NOW WILL
MAINTAIN CURRENT TRENDS INTO THE OVERNIGHT HOURS. WINDS REMAIN
WESTERLY TO NORTHWESTERLY FOR MOST OF THE PERIOD...BUT BY TOMORROW
A WEAKENING PRESSURE GRADIENT MAY ALLOW WINDS TO GO VARIABLE FOR A
TIME...BUT LIKELY CONTINUE TO FAVOR A WESTERLY COMPONENT.

LENNING


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* HIGHER CONFIDENCE IN WIND TRENDS.

LENNING

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO








000
FXUS63 KLOT 171603
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1003 AM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* MVFR CIGS THRU TONIGHT.
* GUSTY WEST/NORTHWEST WINDS THRU EARLY AFTERNOON.

LENNING/CMS

//DISCUSSION...UPDATED 12Z...

MAIN FORECAST CONCERN WILL BE WHEN MVFR CIGS WILL SCATTER OUT.
BACK EDGE STILL ACROSS CENTRAL IA AND EASTERN MN AND MAKING VERY
SLOW PROGRESS TO THE SOUTHEAST. FORECAST SOUNDINGS STILL SUGGEST
INVERSION ALOFT WILL BE STRONG ENOUGH TO TRAP THESE CLOUDS FOR
MOST OF THE DAYLIGHT HOURS AND POSSIBLY INTO THIS EVENING. SO
OPTED TO MAINTAIN MVFR CIGS INTO TONIGHT WITH SOME SCATTERING OR
CLEARING POSSIBLE OVERNIGHT...WHICH WILL LIKELY OCCUR FIRST AT RFD
AND POSSIBLY AS EARLY AS THIS EVENING.

A FEW FLURRIES WILL BE POSSIBLE THIS MORNING...BUT NO RESTRICTIONS
TO VIS EXPECTED.

WEST/NORTHWEST WINDS HAVE DIMINISHED SOME DURING THE EARLY MORNING
HOURS AND EXPECT THEM TO REMAIN GENERALLY STEADY INTO THIS
AFTERNOON...IN THE 10-15KT RANGE WITH GUSTS INTO THE MID/UPPER
TEENS. WINDS WILL SLOWLY DIMINISH THIS AFTERNOON THROUGH TONIGHT
AS THE GRADIENT SLOWLY WEAKENS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD.

LENNING/CMS

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 171603
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1003 AM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* MVFR CIGS THRU TONIGHT.
* GUSTY WEST/NORTHWEST WINDS THRU EARLY AFTERNOON.

LENNING/CMS

//DISCUSSION...UPDATED 12Z...

MAIN FORECAST CONCERN WILL BE WHEN MVFR CIGS WILL SCATTER OUT.
BACK EDGE STILL ACROSS CENTRAL IA AND EASTERN MN AND MAKING VERY
SLOW PROGRESS TO THE SOUTHEAST. FORECAST SOUNDINGS STILL SUGGEST
INVERSION ALOFT WILL BE STRONG ENOUGH TO TRAP THESE CLOUDS FOR
MOST OF THE DAYLIGHT HOURS AND POSSIBLY INTO THIS EVENING. SO
OPTED TO MAINTAIN MVFR CIGS INTO TONIGHT WITH SOME SCATTERING OR
CLEARING POSSIBLE OVERNIGHT...WHICH WILL LIKELY OCCUR FIRST AT RFD
AND POSSIBLY AS EARLY AS THIS EVENING.

A FEW FLURRIES WILL BE POSSIBLE THIS MORNING...BUT NO RESTRICTIONS
TO VIS EXPECTED.

WEST/NORTHWEST WINDS HAVE DIMINISHED SOME DURING THE EARLY MORNING
HOURS AND EXPECT THEM TO REMAIN GENERALLY STEADY INTO THIS
AFTERNOON...IN THE 10-15KT RANGE WITH GUSTS INTO THE MID/UPPER
TEENS. WINDS WILL SLOWLY DIMINISH THIS AFTERNOON THROUGH TONIGHT
AS THE GRADIENT SLOWLY WEAKENS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD.

LENNING/CMS

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 171411
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
811 AM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* MVFR CIGS THRU TONIGHT.
* GUSTY WEST/NORTHWEST WINDS THRU EARLY AFTERNOON.

LENNING/CMS

//DISCUSSION...UPDATED 12Z...

MAIN FORECAST CONCERN WILL BE WHEN MVFR CIGS WILL SCATTER OUT.
BACK EDGE STILL ACROSS CENTRAL IA AND EASTERN MN AND MAKING VERY
SLOW PROGRESS TO THE SOUTHEAST. FORECAST SOUNDINGS STILL SUGGEST
INVERSION ALOFT WILL BE STRONG ENOUGH TO TRAP THESE CLOUDS FOR
MOST OF THE DAYLIGHT HOURS AND POSSIBLY INTO THIS EVENING. SO
OPTED TO MAINTAIN MVFR CIGS INTO TONIGHT WITH SOME SCATTERING OR
CLEARING POSSIBLE OVERNIGHT...WHICH WILL LIKELY OCCUR FIRST AT RFD
AND POSSIBLY AS EARLY AS THIS EVENING.

A FEW FLURRIES WILL BE POSSIBLE THIS MORNING...BUT NO RESTRICTIONS
TO VIS EXPECTED.

WEST/NORTHWEST WINDS HAVE DIMINISHED SOME DURING THE EARLY MORNING
HOURS AND EXPECT THEM TO REMAIN GENERALLY STEADY INTO THIS
AFTERNOON...IN THE 10-15KT RANGE WITH GUSTS INTO THE MID/UPPER
TEENS. WINDS WILL SLOWLY DIMINISH THIS AFTERNOON THROUGH TONIGHT
AS THE GRADIENT SLOWLY WEAKENS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD.

LENNING/CMS

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 171133
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
533 AM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* MVFR CIGS THRU TONIGHT.
* GUSTY WEST/NORTHWEST WINDS THRU EARLY AFTERNOON. CMS

//DISCUSSION...UPDATED 12Z...

MAIN FORECAST CONCERN WILL BE WHEN MVFR CIGS WILL SCATTER OUT.
BACK EDGE STILL ACROSS CENTRAL IA AND EASTERN MN AND MAKING VERY
SLOW PROGRESS TO THE SOUTHEAST. FORECAST SOUNDINGS STILL SUGGEST
INVERSION ALOFT WILL BE STRONG ENOUGH TO TRAP THESE CLOUDS FOR
MOST OF THE DAYLIGHT HOURS AND POSSIBLY INTO THIS EVENING. SO
OPTED TO MAINTAIN MVFR CIGS INTO TONIGHT WITH SOME SCATTERING OR
CLEARING POSSIBLE OVERNIGHT...WHICH WILL LIKELY OCCUR FIRST AT RFD
AND POSSIBLY AS EARLY AS THIS EVENING.

A FEW FLURRIES WILL BE POSSIBLE THIS MORNING...BUT NO RESTRICTIONS
TO VIS EXPECTED.

WEST/NORTHWEST WINDS HAVE DIMINISHED SOME DURING THE EARLY MORNING
HOURS AND EXPECT THEM TO REMAIN GENERALLY STEADY INTO THIS
AFTERNOON...IN THE 10-15KT RANGE WITH GUSTS INTO THE MID/UPPER
TEENS. WINDS WILL SLOWLY DIMINISH THIS AFTERNOON THROUGH TONIGHT
AS THE GRADIENT SLOWLY WEAKENS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 171133
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
533 AM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* MVFR CIGS THRU TONIGHT.
* GUSTY WEST/NORTHWEST WINDS THRU EARLY AFTERNOON. CMS

//DISCUSSION...UPDATED 12Z...

MAIN FORECAST CONCERN WILL BE WHEN MVFR CIGS WILL SCATTER OUT.
BACK EDGE STILL ACROSS CENTRAL IA AND EASTERN MN AND MAKING VERY
SLOW PROGRESS TO THE SOUTHEAST. FORECAST SOUNDINGS STILL SUGGEST
INVERSION ALOFT WILL BE STRONG ENOUGH TO TRAP THESE CLOUDS FOR
MOST OF THE DAYLIGHT HOURS AND POSSIBLY INTO THIS EVENING. SO
OPTED TO MAINTAIN MVFR CIGS INTO TONIGHT WITH SOME SCATTERING OR
CLEARING POSSIBLE OVERNIGHT...WHICH WILL LIKELY OCCUR FIRST AT RFD
AND POSSIBLY AS EARLY AS THIS EVENING.

A FEW FLURRIES WILL BE POSSIBLE THIS MORNING...BUT NO RESTRICTIONS
TO VIS EXPECTED.

WEST/NORTHWEST WINDS HAVE DIMINISHED SOME DURING THE EARLY MORNING
HOURS AND EXPECT THEM TO REMAIN GENERALLY STEADY INTO THIS
AFTERNOON...IN THE 10-15KT RANGE WITH GUSTS INTO THE MID/UPPER
TEENS. WINDS WILL SLOWLY DIMINISH THIS AFTERNOON THROUGH TONIGHT
AS THE GRADIENT SLOWLY WEAKENS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 170915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
315 AM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* GUSTY WEST/NORTHWEST WINDS THRU THIS AFTERNOON.
* MVFR CIGS THRU THIS AFTERNOON. CMS

//DISCUSSION...UPDATED 09Z...

MVFR CIGS HAVE TRENDED A BIT LOWER...NOW IN THE 1500FT RANGE. NOT
EXPECTING IFR CIGS...BUT THEY COULD CONTINUE TO LOWER INTO THE
1000-1200FT RANGE OVER THE NEXT FEW HOURS. ALSO A FEW FLURRIES AT
TIMES...BUT NO RESTRICTION TO VIS EXPECTED. CMS

PREVIOUS 06Z DISCUSSION...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 170915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
315 AM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* GUSTY WEST/NORTHWEST WINDS THRU THIS AFTERNOON.
* MVFR CIGS THRU THIS AFTERNOON. CMS

//DISCUSSION...UPDATED 09Z...

MVFR CIGS HAVE TRENDED A BIT LOWER...NOW IN THE 1500FT RANGE. NOT
EXPECTING IFR CIGS...BUT THEY COULD CONTINUE TO LOWER INTO THE
1000-1200FT RANGE OVER THE NEXT FEW HOURS. ALSO A FEW FLURRIES AT
TIMES...BUT NO RESTRICTION TO VIS EXPECTED. CMS

PREVIOUS 06Z DISCUSSION...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 170915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
315 AM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* GUSTY WEST/NORTHWEST WINDS THRU THIS AFTERNOON.
* MVFR CIGS THRU THIS AFTERNOON. CMS

//DISCUSSION...UPDATED 09Z...

MVFR CIGS HAVE TRENDED A BIT LOWER...NOW IN THE 1500FT RANGE. NOT
EXPECTING IFR CIGS...BUT THEY COULD CONTINUE TO LOWER INTO THE
1000-1200FT RANGE OVER THE NEXT FEW HOURS. ALSO A FEW FLURRIES AT
TIMES...BUT NO RESTRICTION TO VIS EXPECTED. CMS

PREVIOUS 06Z DISCUSSION...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 170915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
315 AM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* GUSTY WEST/NORTHWEST WINDS THRU THIS AFTERNOON.
* MVFR CIGS THRU THIS AFTERNOON. CMS

//DISCUSSION...UPDATED 09Z...

MVFR CIGS HAVE TRENDED A BIT LOWER...NOW IN THE 1500FT RANGE. NOT
EXPECTING IFR CIGS...BUT THEY COULD CONTINUE TO LOWER INTO THE
1000-1200FT RANGE OVER THE NEXT FEW HOURS. ALSO A FEW FLURRIES AT
TIMES...BUT NO RESTRICTION TO VIS EXPECTED. CMS

PREVIOUS 06Z DISCUSSION...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 170909
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
309 AM CST WED DEC 17 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* GUSTY WEST/NORTHWEST WINDS THRU THIS AFTERNOON.
* MVFR CIGS THRU THIS AFTERNOON. CMS

//DISCUSSION...UPDATED 09Z...

MVFR CIGS HAVE TRENDED A BIT LOWER...NOW IN THE 1500FT RANGE. NOT
EXPECTING IFR CIGS...BUT THEY COULD CONTINUE TO LOWER INTO THE
1000-1200FT RANGE OVER THE NEXT FEW HOURS. ALSO A FEW FLURRIES AT
TIMES...BUT NO RESTRICTION TO VIS EXPECTED. CMS

PREVIOUS 06Z DISCUSSION...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 170909
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
309 AM CST WED DEC 17 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* GUSTY WEST/NORTHWEST WINDS THRU THIS AFTERNOON.
* MVFR CIGS THRU THIS AFTERNOON. CMS

//DISCUSSION...UPDATED 09Z...

MVFR CIGS HAVE TRENDED A BIT LOWER...NOW IN THE 1500FT RANGE. NOT
EXPECTING IFR CIGS...BUT THEY COULD CONTINUE TO LOWER INTO THE
1000-1200FT RANGE OVER THE NEXT FEW HOURS. ALSO A FEW FLURRIES AT
TIMES...BUT NO RESTRICTION TO VIS EXPECTED. CMS

PREVIOUS 06Z DISCUSSION...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 170909
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
309 AM CST WED DEC 17 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* GUSTY WEST/NORTHWEST WINDS THRU THIS AFTERNOON.
* MVFR CIGS THRU THIS AFTERNOON. CMS

//DISCUSSION...UPDATED 09Z...

MVFR CIGS HAVE TRENDED A BIT LOWER...NOW IN THE 1500FT RANGE. NOT
EXPECTING IFR CIGS...BUT THEY COULD CONTINUE TO LOWER INTO THE
1000-1200FT RANGE OVER THE NEXT FEW HOURS. ALSO A FEW FLURRIES AT
TIMES...BUT NO RESTRICTION TO VIS EXPECTED. CMS

PREVIOUS 06Z DISCUSSION...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 170909
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
309 AM CST WED DEC 17 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* GUSTY WEST/NORTHWEST WINDS THRU THIS AFTERNOON.
* MVFR CIGS THRU THIS AFTERNOON. CMS

//DISCUSSION...UPDATED 09Z...

MVFR CIGS HAVE TRENDED A BIT LOWER...NOW IN THE 1500FT RANGE. NOT
EXPECTING IFR CIGS...BUT THEY COULD CONTINUE TO LOWER INTO THE
1000-1200FT RANGE OVER THE NEXT FEW HOURS. ALSO A FEW FLURRIES AT
TIMES...BUT NO RESTRICTION TO VIS EXPECTED. CMS

PREVIOUS 06Z DISCUSSION...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 170810
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
210 AM CST WED DEC 17 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* GUSTY NORTHWEST WINDS THRU WEDNESDAY AFTERNOON.
* MVFR CIGS THRU WEDNESDAY AFTERNOON. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 170810
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
210 AM CST WED DEC 17 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* GUSTY NORTHWEST WINDS THRU WEDNESDAY AFTERNOON.
* MVFR CIGS THRU WEDNESDAY AFTERNOON. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 170810
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
210 AM CST WED DEC 17 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* GUSTY NORTHWEST WINDS THRU WEDNESDAY AFTERNOON.
* MVFR CIGS THRU WEDNESDAY AFTERNOON. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 170810
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
210 AM CST WED DEC 17 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* GUSTY NORTHWEST WINDS THRU WEDNESDAY AFTERNOON.
* MVFR CIGS THRU WEDNESDAY AFTERNOON. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 170810
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
210 AM CST WED DEC 17 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* GUSTY NORTHWEST WINDS THRU WEDNESDAY AFTERNOON.
* MVFR CIGS THRU WEDNESDAY AFTERNOON. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 170810
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
210 AM CST WED DEC 17 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* GUSTY NORTHWEST WINDS THRU WEDNESDAY AFTERNOON.
* MVFR CIGS THRU WEDNESDAY AFTERNOON. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 170527
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1127 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* GUSTY NORTHWEST WINDS THRU WEDNESDAY AFTERNOON.
* MVFR CIGS THRU WEDNESDAY AFTERNOON. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 170527
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1127 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* GUSTY NORTHWEST WINDS THRU WEDNESDAY AFTERNOON.
* MVFR CIGS THRU WEDNESDAY AFTERNOON. CMS

//DISCUSSION...UPDATED 06Z...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN
     UNTIL 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN
     UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 170309
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
909 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

*NONE.

KJB

//DISCUSSION...UPDATED 00Z...

GUSTY WEST-NORTHWESTERLY WINDS WILL CONTINUE INTO TONIGHT AS SURFACE
LOW PRESSURE CONTINUES TO SHIFT OVER THE EASTERN GREAT LAKES REGION.
WIND SPEEDS SHOULD BEGIN TO ABATE LATER TONIGHT INTO WEDNESDAY AS A
SURFACE RIDGE OF HIGH PRESSURE BEGINS TO BUILD ACROSS THE REGION.
CIGS ACROSS THE AREA SHOULD ALSO BE ON AN IMPROVING TREND INTO
WEDNESDAY...WITH CLOUD COVER EVEN POSSIBLY BREAKING UP BY
AFTERNOON.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH WITH ALL ELEMENTS.

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 170309
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
909 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

*NONE.

KJB

//DISCUSSION...UPDATED 00Z...

GUSTY WEST-NORTHWESTERLY WINDS WILL CONTINUE INTO TONIGHT AS SURFACE
LOW PRESSURE CONTINUES TO SHIFT OVER THE EASTERN GREAT LAKES REGION.
WIND SPEEDS SHOULD BEGIN TO ABATE LATER TONIGHT INTO WEDNESDAY AS A
SURFACE RIDGE OF HIGH PRESSURE BEGINS TO BUILD ACROSS THE REGION.
CIGS ACROSS THE AREA SHOULD ALSO BE ON AN IMPROVING TREND INTO
WEDNESDAY...WITH CLOUD COVER EVEN POSSIBLY BREAKING UP BY
AFTERNOON.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH WITH ALL ELEMENTS.

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 162301 CCA
AFDLOT

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
459 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

*NONE.

KJB

//DISCUSSION...UPDATED 00Z...

GUSTY WEST-NORTHWESTERLY WINDS WILL CONTINUE INTO TONIGHT AS SURFACE
LOW PRESSURE CONTINUES TO SHIFT OVER THE EASTERN GREAT LAKES REGION.
WIND SPEEDS SHOULD BEGIN TO ABATE LATER TONIGHT INTO WEDNESDAY AS A
SURFACE RIDGE OF HIGH PRESSURE BEGINS TO BUILD ACROSS THE REGION.
CIGS ACROSS THE AREA SHOULD ALSO BE ON AN IMPROVING TREND INTO
WEDNESDAY...WITH CLOUD COVER EVEN POSSIBLY BREAKING UP BY
AFTERNOON.

KJB


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH WITH ALL ELEMENTS.

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO








000
FXUS63 KLOT 162301 CCA
AFDLOT

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
459 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

*NONE.

KJB

//DISCUSSION...UPDATED 00Z...

GUSTY WEST-NORTHWESTERLY WINDS WILL CONTINUE INTO TONIGHT AS SURFACE
LOW PRESSURE CONTINUES TO SHIFT OVER THE EASTERN GREAT LAKES REGION.
WIND SPEEDS SHOULD BEGIN TO ABATE LATER TONIGHT INTO WEDNESDAY AS A
SURFACE RIDGE OF HIGH PRESSURE BEGINS TO BUILD ACROSS THE REGION.
CIGS ACROSS THE AREA SHOULD ALSO BE ON AN IMPROVING TREND INTO
WEDNESDAY...WITH CLOUD COVER EVEN POSSIBLY BREAKING UP BY
AFTERNOON.

KJB


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH WITH ALL ELEMENTS.

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO









000
FXUS63 KLOT 162256
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
456 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

*NONE.

KJB

//DISCUSSION...UPDATED 00Z...

GUSTY WEST-NORTHWESTERLY WINDS WILL CONTINUE INTO TONIGHT AS SURFACE
LOW PRESSURE CONTINUES TO SHIFT OVER THE EASTERN GREAT LAKES REGION.
WIND SPEEDS SHOULD BEGIN TO ABATE LATER TONIGHT INTO WEDNESDAY AS A
SURFACE RIDGE OF HIGH PRESSURE BEGINS TO BUILD ACROSS THE REGION.
CIGS ACROSS THE AREA SHOULD ALSO BE ON AN IMPROVING TREND INTO
WEDNESDAY...WITH CLOUD COVER EVENING POSSIBLY BREAKING UP BY
AFTERNOON.

KJB


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH WITH ALL ELEMENTS.

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 162256
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
456 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

*NONE.

KJB

//DISCUSSION...UPDATED 00Z...

GUSTY WEST-NORTHWESTERLY WINDS WILL CONTINUE INTO TONIGHT AS SURFACE
LOW PRESSURE CONTINUES TO SHIFT OVER THE EASTERN GREAT LAKES REGION.
WIND SPEEDS SHOULD BEGIN TO ABATE LATER TONIGHT INTO WEDNESDAY AS A
SURFACE RIDGE OF HIGH PRESSURE BEGINS TO BUILD ACROSS THE REGION.
CIGS ACROSS THE AREA SHOULD ALSO BE ON AN IMPROVING TREND INTO
WEDNESDAY...WITH CLOUD COVER EVENING POSSIBLY BREAKING UP BY
AFTERNOON.

KJB


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH WITH ALL ELEMENTS.

KJB

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 162158
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
358 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON/EVENING.

RODRIGUEZ/KB

//DISCUSSION...UPDATED 18Z...

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ/KB

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 162158
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
358 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON/EVENING.

RODRIGUEZ/KB

//DISCUSSION...UPDATED 18Z...

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ/KB

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 162114
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
314 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* LINGERING SHOWERS EXITING THIS AFTERNOON.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH SHOWER TRENDS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 162114
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
314 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* LINGERING SHOWERS EXITING THIS AFTERNOON.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH SHOWER TRENDS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO








000
FXUS63 KLOT 162114
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
314 PM CST TUE DEC 16 2014

.SHORT TERM...
313 PM CST

TONIGHT THROUGH FRIDAY...

FILLING SURFACE LOW WAS OFF TO OUR EAST ACROSS THE CENTRAL GREAT
LAKES THIS AFTERNOON...BENEATH WEAKENING UPPER LEVEL LOW WHICH IS IN
THE PROCESS OF MERGING WITH STRONG DIGGING SHORT WAVE OVER THE UPPER
MISSISSIPPI VALLEY. THIS SECOND WAVE IS PROGGED TO SHEAR SOUTHEAST
ACROSS THE REGION TO THE EAST-SOUTHEAST AS IT REDEVELOPS INTO
REMNANT UPPER TROUGH TO THE EAST. VISIBLE SATELLITE IMAGERY SHOWS
MOST OF THE DEEPER CLOUD COVER HAS MOVED OFF TO THE EAST OF THE
FORECAST AREA...ALONG WITH THE BRUNT OF THE RADAR DETECTABLE
PRECIPITATION. EXPECT SOME PATCHY LIGHT RAIN/DRIZZLE AND PERHAPS A
FEW WET FLURRIES TO GRADUALLY END ACROSS THE AREA OVER THE NEXT FEW
HOURS AS MID-LEVELS CONTINUE TO DRY OUT...WITH 12Z RAOBS FROM
UPSTREAM LOCATIONS SUCH AS ABR AND OAX INDICATIVE OF MUCH DRIER AIR
ABOVE THE BOUNDARY LAYER. OTHERWISE...BLUSTERY WEST-NORTHWEST WINDS
WILL CONTINUE TO PULL COLDER AND DRIER AIR INTO THE AREA TONIGHT
WITH WINDS SLOW TO DIMINISH DUE TO LINGERING SURFACE TROUGHING
ACROSS THE UPPER MIDWEST. THOUGH REMAINING MOISTURE WILL BE SHALLOW
IT APPEARS CLOUD COVER WILL LINGER AT LEAST INTO EARLY WEDNESDAY
BEFORE STRONGER SUBSIDENCE CAN ERODE AND SCATTER CLOUDS MORE
EFFECTIVELY. DESPITE CLOUDS...UPSTREAM TEMPS ACROSS EASTERN IA ARE
ONLY IN THE LOW TO MID 20S AT THIS HOUR...SETTING THE STAGE FOR
CHILLIER TEMPS TONIGHT.

SHEARED MID-LEVEL VORTICITY AXIS FROM SHEARING UPPER MIDWEST SHORT
WAVE REMAINS OVER AREA WEDNESDAY..THOUGH HEIGHT RISES DO DEVELOP AS
THE NEW UPPER LOW DEEPENS OVER NEW ENGLAND. THIS ALLOWS THE GRADIENT
TO WEAKEN MORE QUICKLY ESPECIALLY DURING THE AFTERNOON AND
CONTINUING WEDNESDAY NIGHT AS SURFACE HIGH PRESSURE RIDGE MOVES
SLOWLY INTO WESTERN AND CENTRAL ILLINOIS. GUIDANCE DOES DEPICT A
SHORT WAVE APPROACHING FROM THE SOUTHERN PLAINS/LOWER MISSOURI
VALLEY AREA WEDNESDAY NIGHT...THOUGH THIS WAVE DAMPENS SIGNIFICANTLY
AS IT MOVES INTO THE UPPER RIDGE ACROSS THE MIDWEST. MODEL FORECAST
SOUNDINGS AND TIME-HEIGHT PLOTS INDICATE INCREASING MID-HIGH LEVEL
MOISTURE MAINLY AFTER MIDNIGHT WEDNESDAY NIGHT ACROSS OUR SOUTHWEST.
GUIDANCE (NAM...GFS...ECMWF AND SREF) DOES PRODUCE SOME LIGHT QPF
ACROSS CENTRAL ILLINOIS THURSDAY AS THIS WAVE CONTINUES TO
DEAMPLIFY...THOUGH FORECAST SOUNDINGS INDICATE LOW LEVELS INITIALLY
DRY AND SATURATION APPEARS INCOMPLETE MAKING PRECIP AT THE SURFACE A
LOW PROBABILITY. WEAKENING SURFACE HIGH PRESSURE RIDGE EVENTUALLY
MOVES INTO THE AREA THURSDAY NIGHT AND FRIDAY...ROUNDING OUT A FEW
DAYS OF MAINLY DRY AND SEASONABLY COOLER DAYS.

RATZER

&&

.LONG TERM...
313 PM CST

SATURDAY THROUGH TUESDAY...

ATTENTION TURNS TO A PAIR OF APPROACHING SHORT WAVE TROUGHS IN A
SOMEWHAT SPLIT FLOW REGIME. GUIDANCE HAS TRENDED WEAKER WITH THE
SOUTHERN STREAM DISTURBANCE...WHICH MOVES OUT ACROSS THE SOUTHERN
PLAINS AND GULF COAST STATES THROUGH SATURDAY. DECENT AGREEMENT IN
MODEL SOLUTIONS OF A MORE DIGGING NORTHERN STREAM WAVE COMING OUT OF
THE NORTHERN ROCKIES FRIDAY AND MOVING INTO THE LOWER MISSOURI AND
LOWER OHIO VALLEYS ON SATURDAY. WHILE MAIN SURFACE LOW PRESSURE
DEVELOPS WITH SOUTHERN SYSTEM ALONG THE GULF COAST...NORTHERN STREAM
FORCING DOES INDUCE AN INVERTED TROUGH INTO THE OHIO VALLEY SATURDAY
WHICH CONTINUES TO SUPPORT THE POTENTIAL FOR SOME LIGHT SNOW FROM
SOUTHERN/CENTRAL ILLINOIS INTO NORTHERN INDIANA...POSSIBLY INCLUDING
THE SOUTHEASTERN PART OF OUR CWA AS THE UPPER TROUGH MOVES OVERHEAD.
GUIDANCE STILL FOCUSES GREATER QPF SOUTHEAST OF THE FORECAST AREA...
BUT PRUDENT TO MAINTAIN SLIGHT CHANCES FOR SOME LIGHT ACCUMULATING
SNOW SOUTHEAST OF ABOUT A PONTIAC-VALPARAISO LINE. SURFACE HIGH
PRESSURE RIDGING QUICKLY BUILDS IN BEHIND THIS SYSTEM SATURDAY NIGHT
INTO SUNDAY. TEMPS DO MODERATE TO NORMAL FOR THE WEEKEND...GENERALLY
MID 20S AT NIGHT TO LOW/MID 30S BY DAY.

12Z GFS AND ECMWF RUNS HAVE COME INTO GOOD AGREEMENT IN BRINGING A
MORE AMPLIFIED UPPER TROUGH INTO THE CENTRAL CONUS SUNDAY NIGHT
THROUGH TUESDAY...WITH A STRONGER EMBEDDED SHORT WAVE MOVING ACROSS
THE UPPER MIDWEST LATE MONDAY-TUESDAY WITH DEEPENING LOW PRESSURE
PASSING TO OUR NORTH. THIS RESULTS IN WARMING TEMPERATURES ON
STRENGTHENING SOUTH WINDS...WITH THE POTENTIAL OF RAIN/SNOW CHANGING
TO RAIN BY LATE MONDAY AND CONTINUING TUESDAY AHEAD OF THE
APPROACHING COLD FRONT AS THE LOW MOVES ACROSS THE NORTHERN LAKES.
SOME DETAIL AND SPEED DIFFERENCES DO EXIST BETWEEN MODELS AND MUCH
COULD CHANGE BETWEEN NOW AND MONDAY...THOUGH IT DOES APPEAR THAT
COLDER AIR WOULD SPREAD INTO THE REGION LATER TUESDAY/TUESDAY NIGHT
WITH PRECIPITATION TAPERING OFF AS IT MIXES/CHANGES TO LIGHT SNOW.
COLDER AIR WOULD THEN ARRIVE IN TIME FOR THE CHRISTMAS HOLIDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* LINGERING SHOWERS EXITING THIS AFTERNOON.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH SHOWER TRENDS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 162006
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
206 PM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* LINGERING SHOWERS EXITING THIS AFTERNOON.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH SHOWER TRENDS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 162006
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
206 PM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* LINGERING SHOWERS EXITING THIS AFTERNOON.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH SHOWER TRENDS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 161931
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
131 PM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* LINGERING SHOWERS EXITING THIS AFTERNOON.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH SHOWER TRENDS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 161931
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
131 PM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* LINGERING SHOWERS EXITING THIS AFTERNOON.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH SHOWER TRENDS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 161750
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1150 AM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* LINGERING SHOWERS EXITING THIS AFTERNOON.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH SHOWER TRENDS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 161750
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1150 AM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* LINGERING SHOWERS EXITING THIS AFTERNOON.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH SHOWER TRENDS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 161631
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1031 AM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* MVFR CIGS.
* SHOWERS DIMINISHING BY EARLY AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS THIS AFTERNOON/EVENING.

RODRIGUEZ/CMS

//DISCUSSION...UPDATED 12Z...

BROAD LOW PRESSURE IS NOW CENTERED NEAR SOUTHERN LAKE MICHIGAN AND
WILL CONTINUE MOVING EAST TODAY. SOUTHWESTERLY WINDS HAVE IMPROVED
VISIBILITIES TO A IGQ/LOT/VYS LINE. THIS SHOULD CREEP FAR ENOUGH
NORTH TO IMPROVE THE VIS AT MDW BY 13Z. FURTHER NORTH...INCLUDING
AT ORD/DPA...CONFIDENCE REGARDING SPECIFIC TIMING OF IMPROVEMENT
IS LOW AND HELD ONTO A TEMPO FOR 1/2SM THRU 14Z. BY THAT TIME...
EXPECT PREVAILING VIS TO BE UP TO 2SM...BUT PERHAPS REMAIN THERE
FOR MUCH OF THE MORNING. OVERALL TREND IS UP FROM HERE WITH SOME
TWEAKS TO TIMING AND SPECIFIC VIS/CIGS LIKELY NEEDED.

BULK OF THE PRECIP APPEARS TO BE ENDING BY EARLY THIS AFTERNOON
AND BEFORE ENOUGH COLD AIR IS PLACE TO CHANGE PRECIP OVER TO ANY
SNOW. THUS NO LONGER EXPECTING ANY WINTER PRECIP THIS AFTERNOON.

LIGHT WESTERLY WINDS WILL SHIFT NORTHWEST AND INCREASE TO 10-12KT
THIS MORNING...THEN RAPIDLY INCREASE BY EARLY AFTERNOON AS THE
GRADIENT TIGHTENS. WIND SPEEDS IN THE MID/UPPER TEENS WITH GUSTS
INTO THE MID 20KT RANGE LOOKS ON TRACK AND THESE WILL LIKELY
CONTINUE INTO THIS EVENING...SLOWLY DIMINISHING LATE THIS EVENING
INTO THE OVERNIGHT HOURS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM HIGH FOR CIGS THRU THE PERIOD.
* HIGH FOR VIS TRENDS THIS MORNING.
* HIGH FOR SHOWERS THIS MORNING...MEDIUM FOR THIS AFTERNOON.
* HIGH FOR WIND THRU THE PERIOD.

RODRIGUEZ/CMS

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 161631
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1031 AM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* MVFR CIGS.
* SHOWERS DIMINISHING BY EARLY AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS THIS AFTERNOON/EVENING.

RODRIGUEZ/CMS

//DISCUSSION...UPDATED 12Z...

BROAD LOW PRESSURE IS NOW CENTERED NEAR SOUTHERN LAKE MICHIGAN AND
WILL CONTINUE MOVING EAST TODAY. SOUTHWESTERLY WINDS HAVE IMPROVED
VISIBILITIES TO A IGQ/LOT/VYS LINE. THIS SHOULD CREEP FAR ENOUGH
NORTH TO IMPROVE THE VIS AT MDW BY 13Z. FURTHER NORTH...INCLUDING
AT ORD/DPA...CONFIDENCE REGARDING SPECIFIC TIMING OF IMPROVEMENT
IS LOW AND HELD ONTO A TEMPO FOR 1/2SM THRU 14Z. BY THAT TIME...
EXPECT PREVAILING VIS TO BE UP TO 2SM...BUT PERHAPS REMAIN THERE
FOR MUCH OF THE MORNING. OVERALL TREND IS UP FROM HERE WITH SOME
TWEAKS TO TIMING AND SPECIFIC VIS/CIGS LIKELY NEEDED.

BULK OF THE PRECIP APPEARS TO BE ENDING BY EARLY THIS AFTERNOON
AND BEFORE ENOUGH COLD AIR IS PLACE TO CHANGE PRECIP OVER TO ANY
SNOW. THUS NO LONGER EXPECTING ANY WINTER PRECIP THIS AFTERNOON.

LIGHT WESTERLY WINDS WILL SHIFT NORTHWEST AND INCREASE TO 10-12KT
THIS MORNING...THEN RAPIDLY INCREASE BY EARLY AFTERNOON AS THE
GRADIENT TIGHTENS. WIND SPEEDS IN THE MID/UPPER TEENS WITH GUSTS
INTO THE MID 20KT RANGE LOOKS ON TRACK AND THESE WILL LIKELY
CONTINUE INTO THIS EVENING...SLOWLY DIMINISHING LATE THIS EVENING
INTO THE OVERNIGHT HOURS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM HIGH FOR CIGS THRU THE PERIOD.
* HIGH FOR VIS TRENDS THIS MORNING.
* HIGH FOR SHOWERS THIS MORNING...MEDIUM FOR THIS AFTERNOON.
* HIGH FOR WIND THRU THE PERIOD.

RODRIGUEZ/CMS

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 161409
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
809 AM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* IFR CIGS/VIS LIFTING TO MVFR THIS AFTERNOON.
* SHOWERS DIMINISHING BY EARLY AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS THIS AFTERNOON/EVENING.

RODRIGUEZ/CMS

//DISCUSSION...UPDATED 12Z...

BROAD LOW PRESSURE IS NOW CENTERED NEAR SOUTHERN LAKE MICHIGAN AND
WILL CONTINUE MOVING EAST TODAY. SOUTHWESTERLY WINDS HAVE IMPROVED
VISIBILITIES TO A IGQ/LOT/VYS LINE. THIS SHOULD CREEP FAR ENOUGH
NORTH TO IMPROVE THE VIS AT MDW BY 13Z. FURTHER NORTH...INCLUDING
AT ORD/DPA...CONFIDENCE REGARDING SPECIFIC TIMING OF IMPROVEMENT
IS LOW AND HELD ONTO A TEMPO FOR 1/2SM THRU 14Z. BY THAT TIME...
EXPECT PREVAILING VIS TO BE UP TO 2SM...BUT PERHAPS REMAIN THERE
FOR MUCH OF THE MORNING. OVERALL TREND IS UP FROM HERE WITH SOME
TWEAKS TO TIMING AND SPECIFIC VIS/CIGS LIKELY NEEDED.

BULK OF THE PRECIP APPEARS TO BE ENDING BY EARLY THIS AFTERNOON
AND BEFORE ENOUGH COLD AIR IS PLACE TO CHANGE PRECIP OVER TO ANY
SNOW. THUS NO LONGER EXPECTING ANY WINTER PRECIP THIS AFTERNOON.

LIGHT WESTERLY WINDS WILL SHIFT NORTHWEST AND INCREASE TO 10-12KT
THIS MORNING...THEN RAPIDLY INCREASE BY EARLY AFTERNOON AS THE
GRADIENT TIGHTENS. WIND SPEEDS IN THE MID/UPPER TEENS WITH GUSTS
INTO THE MID 20KT RANGE LOOKS ON TRACK AND THESE WILL LIKELY
CONTINUE INTO THIS EVENING...SLOWLY DIMINISHING LATE THIS EVENING
INTO THE OVERNIGHT HOURS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* MEDIUM HIGH FOR VIS TRENDS THIS MORNING.
* HIGH FOR SHOWERS THIS MORNING...LOW FOR THIS AFTERNOON.
* HIGH FOR WIND THRU THE PERIOD.

RODRIGUEZ/CMS

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 161409
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
809 AM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* IFR CIGS/VIS LIFTING TO MVFR THIS AFTERNOON.
* SHOWERS DIMINISHING BY EARLY AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS THIS AFTERNOON/EVENING.

RODRIGUEZ/CMS

//DISCUSSION...UPDATED 12Z...

BROAD LOW PRESSURE IS NOW CENTERED NEAR SOUTHERN LAKE MICHIGAN AND
WILL CONTINUE MOVING EAST TODAY. SOUTHWESTERLY WINDS HAVE IMPROVED
VISIBILITIES TO A IGQ/LOT/VYS LINE. THIS SHOULD CREEP FAR ENOUGH
NORTH TO IMPROVE THE VIS AT MDW BY 13Z. FURTHER NORTH...INCLUDING
AT ORD/DPA...CONFIDENCE REGARDING SPECIFIC TIMING OF IMPROVEMENT
IS LOW AND HELD ONTO A TEMPO FOR 1/2SM THRU 14Z. BY THAT TIME...
EXPECT PREVAILING VIS TO BE UP TO 2SM...BUT PERHAPS REMAIN THERE
FOR MUCH OF THE MORNING. OVERALL TREND IS UP FROM HERE WITH SOME
TWEAKS TO TIMING AND SPECIFIC VIS/CIGS LIKELY NEEDED.

BULK OF THE PRECIP APPEARS TO BE ENDING BY EARLY THIS AFTERNOON
AND BEFORE ENOUGH COLD AIR IS PLACE TO CHANGE PRECIP OVER TO ANY
SNOW. THUS NO LONGER EXPECTING ANY WINTER PRECIP THIS AFTERNOON.

LIGHT WESTERLY WINDS WILL SHIFT NORTHWEST AND INCREASE TO 10-12KT
THIS MORNING...THEN RAPIDLY INCREASE BY EARLY AFTERNOON AS THE
GRADIENT TIGHTENS. WIND SPEEDS IN THE MID/UPPER TEENS WITH GUSTS
INTO THE MID 20KT RANGE LOOKS ON TRACK AND THESE WILL LIKELY
CONTINUE INTO THIS EVENING...SLOWLY DIMINISHING LATE THIS EVENING
INTO THE OVERNIGHT HOURS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* MEDIUM HIGH FOR VIS TRENDS THIS MORNING.
* HIGH FOR SHOWERS THIS MORNING...LOW FOR THIS AFTERNOON.
* HIGH FOR WIND THRU THE PERIOD.

RODRIGUEZ/CMS

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 161206
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
606 AM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* LIFR/VLIFR CIGS/VIS LIFTING TO IFR BY LATE MORNING AND TO MVFR
  THIS AFTERNOON.
* SHOWERS DIMINISHING BY EARLY AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS THIS AFTERNOON/EVENING. CMS

//DISCUSSION...UPDATED 12Z...

BROAD LOW PRESSURE IS NOW CENTERED NEAR SOUTHERN LAKE MICHIGAN AND
WILL CONTINUE MOVING EAST TODAY. SOUTHWESTERLY WINDS HAVE IMPROVED
VISIBILITIES TO A IGQ/LOT/VYS LINE. THIS SHOULD CREEP FAR ENOUGH
NORTH TO IMPROVE THE VIS AT MDW BY 13Z. FURTHER NORTH...INCLUDING
AT ORD/DPA...CONFIDENCE REGARDING SPECIFIC TIMING OF IMPROVEMENT
IS LOW AND HELD ONTO A TEMPO FOR 1/2SM THRU 14Z. BY THAT TIME...
EXPECT PREVAILING VIS TO BE UP TO 2SM...BUT PERHAPS REMAIN THERE
FOR MUCH OF THE MORNING. OVERALL TREND IS UP FROM HERE WITH SOME
TWEAKS TO TIMING AND SPECIFIC VIS/CIGS LIKELY NEEDED.

BULK OF THE PRECIP APPEARS TO BE ENDING BY EARLY THIS AFTERNOON
AND BEFORE ENOUGH COLD AIR IS PLACE TO CHANGE PRECIP OVER TO ANY
SNOW. THUS NO LONGER EXPECTING ANY WINTER PRECIP THIS AFTERNOON.

LIGHT WESTERLY WINDS WILL SHIFT NORTHWEST AND INCREASE TO 10-12KT
THIS MORNING...THEN RAPIDLY INCREASE BY EARLY AFTERNOON AS THE
GRADIENT TIGHTENS. WIND SPEEDS IN THE MID/UPPER TEENS WITH GUSTS
INTO THE MID 20KT RANGE LOOKS ON TRACK AND THESE WILL LIKELY
CONTINUE INTO THIS EVENING...SLOWLY DIMINISHING LATE THIS EVENING
INTO THE OVERNIGHT HOURS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* MEDIUM FOR VIS TRENDS THIS MORNING.
* HIGH FOR SHOWERS THIS MORNING...LOW FOR THIS AFTERNOON.
* HIGH FOR WIND THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 161206
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
606 AM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* LIFR/VLIFR CIGS/VIS LIFTING TO IFR BY LATE MORNING AND TO MVFR
  THIS AFTERNOON.
* SHOWERS DIMINISHING BY EARLY AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS THIS AFTERNOON/EVENING. CMS

//DISCUSSION...UPDATED 12Z...

BROAD LOW PRESSURE IS NOW CENTERED NEAR SOUTHERN LAKE MICHIGAN AND
WILL CONTINUE MOVING EAST TODAY. SOUTHWESTERLY WINDS HAVE IMPROVED
VISIBILITIES TO A IGQ/LOT/VYS LINE. THIS SHOULD CREEP FAR ENOUGH
NORTH TO IMPROVE THE VIS AT MDW BY 13Z. FURTHER NORTH...INCLUDING
AT ORD/DPA...CONFIDENCE REGARDING SPECIFIC TIMING OF IMPROVEMENT
IS LOW AND HELD ONTO A TEMPO FOR 1/2SM THRU 14Z. BY THAT TIME...
EXPECT PREVAILING VIS TO BE UP TO 2SM...BUT PERHAPS REMAIN THERE
FOR MUCH OF THE MORNING. OVERALL TREND IS UP FROM HERE WITH SOME
TWEAKS TO TIMING AND SPECIFIC VIS/CIGS LIKELY NEEDED.

BULK OF THE PRECIP APPEARS TO BE ENDING BY EARLY THIS AFTERNOON
AND BEFORE ENOUGH COLD AIR IS PLACE TO CHANGE PRECIP OVER TO ANY
SNOW. THUS NO LONGER EXPECTING ANY WINTER PRECIP THIS AFTERNOON.

LIGHT WESTERLY WINDS WILL SHIFT NORTHWEST AND INCREASE TO 10-12KT
THIS MORNING...THEN RAPIDLY INCREASE BY EARLY AFTERNOON AS THE
GRADIENT TIGHTENS. WIND SPEEDS IN THE MID/UPPER TEENS WITH GUSTS
INTO THE MID 20KT RANGE LOOKS ON TRACK AND THESE WILL LIKELY
CONTINUE INTO THIS EVENING...SLOWLY DIMINISHING LATE THIS EVENING
INTO THE OVERNIGHT HOURS. CMS

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* MEDIUM FOR VIS TRENDS THIS MORNING.
* HIGH FOR SHOWERS THIS MORNING...LOW FOR THIS AFTERNOON.
* HIGH FOR WIND THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
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000
FXUS63 KLOT 160930
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
330 AM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* LIFR CIGS/IFR VIS THRU MID MORNING LIFTING TO IFR BY LATE
  MORNING AND MVFR BY MID AFTERNOON.
* SHOWERS/DRIZZLE THRU LATE MORNING.
* SMALL CHANCE OF LIGHT SNOW MIXING WITH LIGHT RAIN EARLY THIS
  AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS THIS AFTERNOON/EVENING. CMS

//DISCUSSION...UPDATED 09Z...

CIGS HAVE BEEN STEADY IN THE 200-400 FT RANGE WHILE VIS HAS BEEN
STEADY IN THE 1SM-2SM RANGE...WITH SOME POCKETS OF LOWER VIS.
THESE CONDITIONS LOOK LIKE THEY WILL PREVAIL UNTIL THE LOW PASSES
EAST OF THE TERMINALS...WHICH SHOULD OCCUR AFTER 12Z OR 13Z. CMS

PREVIOUS 06Z DISCUSSION...

LOW PRESSURE CENTERED NEAR THE QUAD CITIES WILL MOVE EAST ACROSS
NORTHERN IL EARLY TUESDAY MORNING AND THEN INTO SOUTHERN LOWER
MICHIGAN LATER TUESDAY MORNING...AS IT SLOWLY WEAKENS. LIFR CIGS
EXPECTED TO CONTINUE UNTIL AFTER THIS LOW MOVES EAST OF THE
TERMINALS. COULD BE SOME BRIEF IMPROVEMENT AS HEAVIER SHOWERS MOVE
THROUGH...BUT TOO UNCERTAIN AND SHORT-LIVED TO INCLUDE IN THE
TAFS. VISIBILITIES HAVE BEEN TRENDING LOWER...NOW GENERALLY IN THE
1SM TO 2SM RANGE. NOT EXPECTING THESE TO GO MUCH LOWER WITH
SHOWERS SPREADING IN FROM THE SOUTHWEST CURRENTLY...BUT WILL NEED
TO MONITOR TRENDS OVER THE NEXT FEW HOURS. FAIRLY WIDESPREAD
SHOWERS OVER EASTERN IOWA ARE FORECAST TO SLOWLY DECREASE IN
COVERAGE PER THE MOST RECENT HI RES GUIDANCE. BUT ENOUGH DRIZZLE
AND PERIODS OF SHOWERS TO JUST CARRY PREVAILING MENTION. AS THE
LOW SHIFTS EAST...CIGS WILL GRADUALLY IMPROVE TO IFR BY LATE
MORNING AND THEN INTO MVFR TUESDAY AFTERNOON BUT EITHER HIGH MVFR
OR LOW VFR CIGS ARE EXPECTED TO CONTINUE THROUGH MUCH OF TUESDAY
TONIGHT.

LIGHT SOUTH/SOUTHEAST WINDS WILL BECOME LIGHT AND VARIABLE OR
PERHAPS CALM AS THE LOW MOVES ACROSS. WINDS WILL THEN SHIFT TO THE
WEST/NORTHWEST BEHIND THE LOW...BUT STRONGER WINDS/GUSTS WILL LAG
THE SHIFT BY AN HR OR TWO. FORECAST SOUNDINGS SUGGEST WIND SPEEDS
INTO THE MID TEENS AND GUSTS INTO THE MID 20KT RANGE AND COULD BE
A BIT HIGHER THAN THIS...ESPECIALLY ACROSS NORTHWEST IL AND RFD.
WINDS SLOWLY DIMINISH THIS EVENING BUT REMAIN GUSTY. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR SHOWERS/DRIZZLE THRU LATE MORNING.
* LOW FOR CHANCE OF LIGHT RAIN MIXING WITH LIGHT SNOW EARLY THIS
  AFTERNOON.
* HIGH FOR WIND SPEEDS/GUSTS...MEDIUM FOR TIMING/CHANGES. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

THURSDAY THROUGH SUNDAY...SOME PERIODIC MVFR CIGS POSSIBLE BUT
PRIMARILY VFR CONDITIONS EXPECTED.

IZZI

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 160930
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
330 AM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* LIFR CIGS/IFR VIS THRU MID MORNING LIFTING TO IFR BY LATE
  MORNING AND MVFR BY MID AFTERNOON.
* SHOWERS/DRIZZLE THRU LATE MORNING.
* SMALL CHANCE OF LIGHT SNOW MIXING WITH LIGHT RAIN EARLY THIS
  AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS THIS AFTERNOON/EVENING. CMS

//DISCUSSION...UPDATED 09Z...

CIGS HAVE BEEN STEADY IN THE 200-400 FT RANGE WHILE VIS HAS BEEN
STEADY IN THE 1SM-2SM RANGE...WITH SOME POCKETS OF LOWER VIS.
THESE CONDITIONS LOOK LIKE THEY WILL PREVAIL UNTIL THE LOW PASSES
EAST OF THE TERMINALS...WHICH SHOULD OCCUR AFTER 12Z OR 13Z. CMS

PREVIOUS 06Z DISCUSSION...

LOW PRESSURE CENTERED NEAR THE QUAD CITIES WILL MOVE EAST ACROSS
NORTHERN IL EARLY TUESDAY MORNING AND THEN INTO SOUTHERN LOWER
MICHIGAN LATER TUESDAY MORNING...AS IT SLOWLY WEAKENS. LIFR CIGS
EXPECTED TO CONTINUE UNTIL AFTER THIS LOW MOVES EAST OF THE
TERMINALS. COULD BE SOME BRIEF IMPROVEMENT AS HEAVIER SHOWERS MOVE
THROUGH...BUT TOO UNCERTAIN AND SHORT-LIVED TO INCLUDE IN THE
TAFS. VISIBILITIES HAVE BEEN TRENDING LOWER...NOW GENERALLY IN THE
1SM TO 2SM RANGE. NOT EXPECTING THESE TO GO MUCH LOWER WITH
SHOWERS SPREADING IN FROM THE SOUTHWEST CURRENTLY...BUT WILL NEED
TO MONITOR TRENDS OVER THE NEXT FEW HOURS. FAIRLY WIDESPREAD
SHOWERS OVER EASTERN IOWA ARE FORECAST TO SLOWLY DECREASE IN
COVERAGE PER THE MOST RECENT HI RES GUIDANCE. BUT ENOUGH DRIZZLE
AND PERIODS OF SHOWERS TO JUST CARRY PREVAILING MENTION. AS THE
LOW SHIFTS EAST...CIGS WILL GRADUALLY IMPROVE TO IFR BY LATE
MORNING AND THEN INTO MVFR TUESDAY AFTERNOON BUT EITHER HIGH MVFR
OR LOW VFR CIGS ARE EXPECTED TO CONTINUE THROUGH MUCH OF TUESDAY
TONIGHT.

LIGHT SOUTH/SOUTHEAST WINDS WILL BECOME LIGHT AND VARIABLE OR
PERHAPS CALM AS THE LOW MOVES ACROSS. WINDS WILL THEN SHIFT TO THE
WEST/NORTHWEST BEHIND THE LOW...BUT STRONGER WINDS/GUSTS WILL LAG
THE SHIFT BY AN HR OR TWO. FORECAST SOUNDINGS SUGGEST WIND SPEEDS
INTO THE MID TEENS AND GUSTS INTO THE MID 20KT RANGE AND COULD BE
A BIT HIGHER THAN THIS...ESPECIALLY ACROSS NORTHWEST IL AND RFD.
WINDS SLOWLY DIMINISH THIS EVENING BUT REMAIN GUSTY. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR SHOWERS/DRIZZLE THRU LATE MORNING.
* LOW FOR CHANCE OF LIGHT RAIN MIXING WITH LIGHT SNOW EARLY THIS
  AFTERNOON.
* HIGH FOR WIND SPEEDS/GUSTS...MEDIUM FOR TIMING/CHANGES. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

THURSDAY THROUGH SUNDAY...SOME PERIODIC MVFR CIGS POSSIBLE BUT
PRIMARILY VFR CONDITIONS EXPECTED.

IZZI

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
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000
FXUS63 KLOT 160916
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
316 AM CST TUE DEC 16 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJIWHARA WITH THE FILLING
SYSTEM TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY
PUSHING SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY
EVENING. OTHER THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER
AIR...NOT MUCH EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR
ABOVE OUR SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER
THROUGH TUESDAY NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW
MOIST LAYER LOOKS TO EVENTUALLY DEVELOP HOLES IN THE CLOUDS
WEDNESDAY. IN COLDER AIR HIGHS WEDNESDAY EXPECTED FROM THE UPPER
20S TO LOWER 30S...OR A LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIME FRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* LIFR CIGS/IFR VIS THRU MID MORNING LIFTING TO IFR BY LATE
  MORNING AND MVFR BY MID AFTERNOON.
* SHOWERS/DRIZZLE THRU LATE MORNING.
* SMALL CHANCE OF LIGHT SNOW MIXING WITH LIGHT RAIN EARLY THIS
  AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS THIS AFTERNOON/EVENING. CMS

//DISCUSSION...UPDATED 09Z...

CIGS HAVE BEEN STEADY IN THE 200-400 FT RANGE WHILE VIS HAS BEEN
STEADY IN THE 1SM-2SM RANGE...WITH SOME POCKETS OF LOWER VIS.
THESE CONDITIONS LOOK LIKE THEY WILL PREVAIL UNTIL THE LOW PASSES
EAST OF THE TERMINALS...WHICH SHOULD OCCUR AFTER 12Z OR 13Z. CMS

PREVIOUS 06Z DISCUSSION...

LOW PRESSURE CENTERED NEAR THE QUAD CITIES WILL MOVE EAST ACROSS
NORTHERN IL EARLY TUESDAY MORNING AND THEN INTO SOUTHERN LOWER
MICHIGAN LATER TUESDAY MORNING...AS IT SLOWLY WEAKENS. LIFR CIGS
EXPECTED TO CONTINUE UNTIL AFTER THIS LOW MOVES EAST OF THE
TERMINALS. COULD BE SOME BRIEF IMPROVEMENT AS HEAVIER SHOWERS MOVE
THROUGH...BUT TOO UNCERTAIN AND SHORT-LIVED TO INCLUDE IN THE
TAFS. VISIBILITIES HAVE BEEN TRENDING LOWER...NOW GENERALLY IN THE
1SM TO 2SM RANGE. NOT EXPECTING THESE TO GO MUCH LOWER WITH
SHOWERS SPREADING IN FROM THE SOUTHWEST CURRENTLY...BUT WILL NEED
TO MONITOR TRENDS OVER THE NEXT FEW HOURS. FAIRLY WIDESPREAD
SHOWERS OVER EASTERN IOWA ARE FORECAST TO SLOWLY DECREASE IN
COVERAGE PER THE MOST RECENT HI RES GUIDANCE. BUT ENOUGH DRIZZLE
AND PERIODS OF SHOWERS TO JUST CARRY PREVAILING MENTION. AS THE
LOW SHIFTS EAST...CIGS WILL GRADUALLY IMPROVE TO IFR BY LATE
MORNING AND THEN INTO MVFR TUESDAY AFTERNOON BUT EITHER HIGH MVFR
OR LOW VFR CIGS ARE EXPECTED TO CONTINUE THROUGH MUCH OF TUESDAY
TONIGHT.

LIGHT SOUTH/SOUTHEAST WINDS WILL BECOME LIGHT AND VARIABLE OR
PERHAPS CALM AS THE LOW MOVES ACROSS. WINDS WILL THEN SHIFT TO THE
WEST/NORTHWEST BEHIND THE LOW...BUT STRONGER WINDS/GUSTS WILL LAG
THE SHIFT BY AN HR OR TWO. FORECAST SOUNDINGS SUGGEST WIND SPEEDS
INTO THE MID TEENS AND GUSTS INTO THE MID 20KT RANGE AND COULD BE
A BIT HIGHER THAN THIS...ESPECIALLY ACROSS NORTHWEST IL AND RFD.
WINDS SLOWLY DIMINISH THIS EVENING BUT REMAIN GUSTY. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR SHOWERS/DRIZZLE THRU LATE MORNING.
* LOW FOR CHANCE OF LIGHT RAIN MIXING WITH LIGHT SNOW EARLY THIS
  AFTERNOON.
* HIGH FOR WIND SPEEDS/GUSTS...MEDIUM FOR TIMING/CHANGES. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

THURSDAY THROUGH SUNDAY...SOME PERIODIC MVFR CIGS POSSIBLE BUT
PRIMARILY VFR CONDITIONS EXPECTED.

IZZI

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
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000
FXUS63 KLOT 160916
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
316 AM CST TUE DEC 16 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJIWHARA WITH THE FILLING
SYSTEM TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY
PUSHING SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY
EVENING. OTHER THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER
AIR...NOT MUCH EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR
ABOVE OUR SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER
THROUGH TUESDAY NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW
MOIST LAYER LOOKS TO EVENTUALLY DEVELOP HOLES IN THE CLOUDS
WEDNESDAY. IN COLDER AIR HIGHS WEDNESDAY EXPECTED FROM THE UPPER
20S TO LOWER 30S...OR A LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIME FRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* LIFR CIGS/IFR VIS THRU MID MORNING LIFTING TO IFR BY LATE
  MORNING AND MVFR BY MID AFTERNOON.
* SHOWERS/DRIZZLE THRU LATE MORNING.
* SMALL CHANCE OF LIGHT SNOW MIXING WITH LIGHT RAIN EARLY THIS
  AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS THIS AFTERNOON/EVENING. CMS

//DISCUSSION...UPDATED 09Z...

CIGS HAVE BEEN STEADY IN THE 200-400 FT RANGE WHILE VIS HAS BEEN
STEADY IN THE 1SM-2SM RANGE...WITH SOME POCKETS OF LOWER VIS.
THESE CONDITIONS LOOK LIKE THEY WILL PREVAIL UNTIL THE LOW PASSES
EAST OF THE TERMINALS...WHICH SHOULD OCCUR AFTER 12Z OR 13Z. CMS

PREVIOUS 06Z DISCUSSION...

LOW PRESSURE CENTERED NEAR THE QUAD CITIES WILL MOVE EAST ACROSS
NORTHERN IL EARLY TUESDAY MORNING AND THEN INTO SOUTHERN LOWER
MICHIGAN LATER TUESDAY MORNING...AS IT SLOWLY WEAKENS. LIFR CIGS
EXPECTED TO CONTINUE UNTIL AFTER THIS LOW MOVES EAST OF THE
TERMINALS. COULD BE SOME BRIEF IMPROVEMENT AS HEAVIER SHOWERS MOVE
THROUGH...BUT TOO UNCERTAIN AND SHORT-LIVED TO INCLUDE IN THE
TAFS. VISIBILITIES HAVE BEEN TRENDING LOWER...NOW GENERALLY IN THE
1SM TO 2SM RANGE. NOT EXPECTING THESE TO GO MUCH LOWER WITH
SHOWERS SPREADING IN FROM THE SOUTHWEST CURRENTLY...BUT WILL NEED
TO MONITOR TRENDS OVER THE NEXT FEW HOURS. FAIRLY WIDESPREAD
SHOWERS OVER EASTERN IOWA ARE FORECAST TO SLOWLY DECREASE IN
COVERAGE PER THE MOST RECENT HI RES GUIDANCE. BUT ENOUGH DRIZZLE
AND PERIODS OF SHOWERS TO JUST CARRY PREVAILING MENTION. AS THE
LOW SHIFTS EAST...CIGS WILL GRADUALLY IMPROVE TO IFR BY LATE
MORNING AND THEN INTO MVFR TUESDAY AFTERNOON BUT EITHER HIGH MVFR
OR LOW VFR CIGS ARE EXPECTED TO CONTINUE THROUGH MUCH OF TUESDAY
TONIGHT.

LIGHT SOUTH/SOUTHEAST WINDS WILL BECOME LIGHT AND VARIABLE OR
PERHAPS CALM AS THE LOW MOVES ACROSS. WINDS WILL THEN SHIFT TO THE
WEST/NORTHWEST BEHIND THE LOW...BUT STRONGER WINDS/GUSTS WILL LAG
THE SHIFT BY AN HR OR TWO. FORECAST SOUNDINGS SUGGEST WIND SPEEDS
INTO THE MID TEENS AND GUSTS INTO THE MID 20KT RANGE AND COULD BE
A BIT HIGHER THAN THIS...ESPECIALLY ACROSS NORTHWEST IL AND RFD.
WINDS SLOWLY DIMINISH THIS EVENING BUT REMAIN GUSTY. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR SHOWERS/DRIZZLE THRU LATE MORNING.
* LOW FOR CHANCE OF LIGHT RAIN MIXING WITH LIGHT SNOW EARLY THIS
  AFTERNOON.
* HIGH FOR WIND SPEEDS/GUSTS...MEDIUM FOR TIMING/CHANGES. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

THURSDAY THROUGH SUNDAY...SOME PERIODIC MVFR CIGS POSSIBLE BUT
PRIMARILY VFR CONDITIONS EXPECTED.

IZZI

&&

.MARINE...

316 AM...LOW PRESSURE OVER NORTHERN ILLINOIS WILL MOVE ACROSS
SOUTHERN LOWER MICHIGAN THIS MORNING. LIGHT WINDS WILL SHIFT TO
THE NORTH/NORTHWEST AND INCREASE FIRST OVER THE NORTHERN HALF OF
THE LAKE AND THEN ACROSS THE REST OF THE LAKE BY EARLY AFTERNOON.
SPEEDS TO 30 KTS LOOK ON TRACK WITH SOME GUSTS TO LOW END GALES
POSSIBLE BUT NOT TOO CONFIDENT ON HOW FREQUENT THEY WILL BECOME
SO MAINTAINED GALE GUST MENTION. HIGH PRESSURE WILL BUILD SOUTH
ACROSS THE PLAINS TONIGHT AND WEDNESDAY AND SLOWLY MOVE EAST OVER
THE LAKES THURSDAY INTO FRIDAY. SO A PROLONGED NORTHWEST WIND IS
EXPECTED WITH SPEEDS GRADUALLY DIMINISHING WEDNESDAY AFTERNOON
THROUGH THURSDAY.

DENSE FOG WILL STILL BE POSSIBLE THROUGH MID MORNING UNTIL THE
WINDS INCREASE AND EXTENDED THE FOG ADVISORY A FEW HOURS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 160549
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1149 PM CST MON DEC 15 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJIWHARA WITH THE FILLING
SYSTEM TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY
PUSHING SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY
EVENING. OTHER THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER
AIR...NOT MUCH EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR
ABOVE OUR SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER
THROUGH TUESDAY NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW
MOIST LAYER LOOKS TO EVENTUALLY DEVELOP HOLES IN THE CLOUDS
WEDNESDAY. IN COLDER AIR HIGHS WEDNESDAY EXPECTED FROM THE UPPER
20S TO LOWER 30S...OR A LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIME FRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* LIFR CIGS/IFR VIS THRU MID TUESDAY MORNING LIFTING TO IFR BY
  LATE MORNING AND MVFR BY MID AFTERNOON.
* SHOWERS/DRIZZLE THRU LATE TUESDAY MORNING.
* SMALL CHANCE OF LIGHT SNOW MIXING WITH LIGHT RAIN EARLY TUESDAY
  AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS TUESDAY AFTERNOON/EVENING. CMS

//DISCUSSION...UPDATED 06Z...

LOW PRESSURE CENTERED NEAR THE QUAD CITIES WILL MOVE EAST ACROSS
NORTHERN IL EARLY TUESDAY MORNING AND THEN INTO SOUTHERN LOWER
MICHIGAN LATER TUESDAY MORNING...AS IT SLOWLY WEAKENS. LIFR CIGS
EXPECTED TO CONTINUE UNTIL AFTER THIS LOW MOVES EAST OF THE
TERMINALS. COULD BE SOME BRIEF IMPROVEMENT AS HEAVIER SHOWERS MOVE
THROUGH...BUT TOO UNCERTAIN AND SHORT-LIVED TO INCLUDE IN THE
TAFS. VISIBILITIES HAVE BEEN TRENDING LOWER...NOW GENERALLY IN THE
1SM TO 2SM RANGE. NOT EXPECTING THESE TO GO MUCH LOWER WITH
SHOWERS SPREADING IN FROM THE SOUTHWEST CURRENTLY...BUT WILL NEED
TO MONITOR TRENDS OVER THE NEXT FEW HOURS. FAIRLY WIDESPREAD
SHOWERS OVER EASTERN IOWA ARE FORECAST TO SLOWLY DECREASE IN
COVERAGE PER THE MOST RECENT HI RES GUIDANCE. BUT ENOUGH DRIZZLE
AND PERIODS OF SHOWERS TO JUST CARRY PREVAILING MENTION. AS THE
LOW SHIFTS EAST...CIGS WILL GRADUALLY IMPROVE TO IFR BY LATE
MORNING AND THEN INTO MVFR TUESDAY AFTERNOON BUT EITHER HIGH MVFR
OR LOW VFR CIGS ARE EXPECTED TO CONTINUE THROUGH MUCH OF TUESDAY
TONIGHT.

LIGHT SOUTH/SOUTHEAST WINDS WILL BECOME LIGHT AND VARIABLE OR
PERHAPS CALM AS THE LOW MOVES ACROSS. WINDS WILL THEN SHIFT TO THE
WEST/NORTHWEST BEHIND THE LOW...BUT STRONGER WINDS/GUSTS WILL LAG
THE SHIFT BY AN HR OR TWO. FORECAST SOUNDINGS SUGGEST WIND SPEEDS
INTO THE MID TEENS AND GUSTS INTO THE MID 20KT RANGE AND COULD BE
A BIT HIGHER THAN THIS...ESPECIALLY ACROSS NORTHWEST IL AND RFD.
WINDS SLOWLY DIMINISH THIS EVENING BUT REMAIN GUSTY. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR SHOWERS/DRIZZLE THRU MID MORNING.
* LOW FOR CHANCE OF LIGHT RAIN MIXING WITH LIGHT SNOW EARLY THIS
  AFTERNOON.
* HIGH FOR WIND SPEEDS/GUSTS...MEDIUM FOR TIMING/CHANGES. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

THURSDAY THROUGH SUNDAY...SOME PERIODIC MVFR CIGS POSSIBLE BUT
PRIMARILY VFR CONDITIONS EXPECTED.

IZZI

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIR MASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 160549
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1149 PM CST MON DEC 15 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJIWHARA WITH THE FILLING
SYSTEM TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY
PUSHING SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY
EVENING. OTHER THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER
AIR...NOT MUCH EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR
ABOVE OUR SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER
THROUGH TUESDAY NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW
MOIST LAYER LOOKS TO EVENTUALLY DEVELOP HOLES IN THE CLOUDS
WEDNESDAY. IN COLDER AIR HIGHS WEDNESDAY EXPECTED FROM THE UPPER
20S TO LOWER 30S...OR A LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIME FRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* LIFR CIGS/IFR VIS THRU MID TUESDAY MORNING LIFTING TO IFR BY
  LATE MORNING AND MVFR BY MID AFTERNOON.
* SHOWERS/DRIZZLE THRU LATE TUESDAY MORNING.
* SMALL CHANCE OF LIGHT SNOW MIXING WITH LIGHT RAIN EARLY TUESDAY
  AFTERNOON.
* STRONG/GUSTY NORTHWEST WINDS TUESDAY AFTERNOON/EVENING. CMS

//DISCUSSION...UPDATED 06Z...

LOW PRESSURE CENTERED NEAR THE QUAD CITIES WILL MOVE EAST ACROSS
NORTHERN IL EARLY TUESDAY MORNING AND THEN INTO SOUTHERN LOWER
MICHIGAN LATER TUESDAY MORNING...AS IT SLOWLY WEAKENS. LIFR CIGS
EXPECTED TO CONTINUE UNTIL AFTER THIS LOW MOVES EAST OF THE
TERMINALS. COULD BE SOME BRIEF IMPROVEMENT AS HEAVIER SHOWERS MOVE
THROUGH...BUT TOO UNCERTAIN AND SHORT-LIVED TO INCLUDE IN THE
TAFS. VISIBILITIES HAVE BEEN TRENDING LOWER...NOW GENERALLY IN THE
1SM TO 2SM RANGE. NOT EXPECTING THESE TO GO MUCH LOWER WITH
SHOWERS SPREADING IN FROM THE SOUTHWEST CURRENTLY...BUT WILL NEED
TO MONITOR TRENDS OVER THE NEXT FEW HOURS. FAIRLY WIDESPREAD
SHOWERS OVER EASTERN IOWA ARE FORECAST TO SLOWLY DECREASE IN
COVERAGE PER THE MOST RECENT HI RES GUIDANCE. BUT ENOUGH DRIZZLE
AND PERIODS OF SHOWERS TO JUST CARRY PREVAILING MENTION. AS THE
LOW SHIFTS EAST...CIGS WILL GRADUALLY IMPROVE TO IFR BY LATE
MORNING AND THEN INTO MVFR TUESDAY AFTERNOON BUT EITHER HIGH MVFR
OR LOW VFR CIGS ARE EXPECTED TO CONTINUE THROUGH MUCH OF TUESDAY
TONIGHT.

LIGHT SOUTH/SOUTHEAST WINDS WILL BECOME LIGHT AND VARIABLE OR
PERHAPS CALM AS THE LOW MOVES ACROSS. WINDS WILL THEN SHIFT TO THE
WEST/NORTHWEST BEHIND THE LOW...BUT STRONGER WINDS/GUSTS WILL LAG
THE SHIFT BY AN HR OR TWO. FORECAST SOUNDINGS SUGGEST WIND SPEEDS
INTO THE MID TEENS AND GUSTS INTO THE MID 20KT RANGE AND COULD BE
A BIT HIGHER THAN THIS...ESPECIALLY ACROSS NORTHWEST IL AND RFD.
WINDS SLOWLY DIMINISH THIS EVENING BUT REMAIN GUSTY. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR SHOWERS/DRIZZLE THRU MID MORNING.
* LOW FOR CHANCE OF LIGHT RAIN MIXING WITH LIGHT SNOW EARLY THIS
  AFTERNOON.
* HIGH FOR WIND SPEEDS/GUSTS...MEDIUM FOR TIMING/CHANGES. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

THURSDAY THROUGH SUNDAY...SOME PERIODIC MVFR CIGS POSSIBLE BUT
PRIMARILY VFR CONDITIONS EXPECTED.

IZZI

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIR MASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 160321
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
921 PM CST MON DEC 15 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJIWHARA WITH THE FILLING
SYSTEM TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY
PUSHING SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY
EVENING. OTHER THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER
AIR...NOT MUCH EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR
ABOVE OUR SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER
THROUGH TUESDAY NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW
MOIST LAYER LOOKS TO EVENTUALLY DEVELOP HOLES IN THE CLOUDS
WEDNESDAY. IN COLDER AIR HIGHS WEDNESDAY EXPECTED FROM THE UPPER
20S TO LOWER 30S...OR A LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIME FRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* GENERALLY IFR CIGS LIKELY TO PERSIST INTO TUESDAY MORNING WITH
  BRIEF LIFR POSSIBLE

IZZI

//DISCUSSION...UPDATED 03...

DESPITE SUNSET HAVE SEEN ONLY A SLIGHT DOWNWARD BUILDING OF CIGS
THIS EVENING AND IN FACT...CIGS HAVE BEEN COMING UP NEAR THE
CENTER OF THE LOW OVER EASTERN IOWA MOVING INTO NORTHWEST
ILLINOIS. CONFIDENCE REMAINS LOW ON EXACT CIG TRENDS...BUT GIVEN
ONLY VERY SPOTTY LIFR CIGS THUS FAR AND LACK OF ANY SIGNIFICANT
LOWERING NOTED IN THE REGION HAVE RAISED FORECAST CIGS OVERNIGHT
BY A COUPLE HUNDRED FEET. A COUPLE BANDS OF SHOWERS WILL PIVOT
THROUGH THE AREA OVERNIGHT INTO EARLY TUES MORNING AND COULD HELP
BRIEFLY SCATTER OUT THE IFR CIGS FOR BRIEF PERIODS OF MVFR.

IZZI

UPDATED 00Z...

SLOW MOVING LOW PRESSURE SYSTEM WILL CONTINUE TO MOVE ACROSS THE
REGION THROUGH THE TAF CYCLE. RECENT IMPROVEMENT TO LOW END MVFR
EXPECTED TO BE TEMPORARY WITH CIGS LIKELY TO DROP BACK TO IFR VERY
NEAR THE 00Z TAF START TIME. WITH DECREASING WINDS AND MOIST LOW
LEVELS WOULD ANTICIPATE CIGS CONTINUING TO BUILD DOWNWARD TO LIFR
LATER THIS EVENING OR OVERNIGHT...THEN LIKELY STAYING THERE INTO
TUESDAY MORNING. WINDS WILL BECOME NORTHWEST AND BEGIN TO INCREASE
MID-LATE TUESDAY MORNING WHICH SHOULD BEGIN THE PROCESS OF
SCOURING OUT THE VERY LOW CIGS WITH IMPROVEMENT TO MVFR LIKELY
TUESDAY. LIKELY TO SEE MISTY/DRIZZLY CONDITIONS WITH THE LOW CIGS
TONIGHT INTO EARLY TUESDAY MORNING WITH AT LEAST OCNL SHOWERS
PIVOTING AROUND THE LOW BEFORE PRECIP CHANCES WANE TOWARD MIDDAY
TUESDAY.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW-MEDIUM CONFIDENCE IN CIGS
* MEDIUM CONFIDENCE IN PRECIP TRENDS
* FAIRLY HIGH CONFIDENCE IN GENERAL WIND TRENDS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

THURSDAY THROUGH SUNDAY...SOME PERIODIC MVFR CIGS POSSIBLE BUT
PRIMARILY VFR CONDITIONS EXPECTED.

IZZI

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIR MASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 160321
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
921 PM CST MON DEC 15 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJIWHARA WITH THE FILLING
SYSTEM TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY
PUSHING SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY
EVENING. OTHER THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER
AIR...NOT MUCH EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR
ABOVE OUR SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER
THROUGH TUESDAY NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW
MOIST LAYER LOOKS TO EVENTUALLY DEVELOP HOLES IN THE CLOUDS
WEDNESDAY. IN COLDER AIR HIGHS WEDNESDAY EXPECTED FROM THE UPPER
20S TO LOWER 30S...OR A LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIME FRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* GENERALLY IFR CIGS LIKELY TO PERSIST INTO TUESDAY MORNING WITH
  BRIEF LIFR POSSIBLE

IZZI

//DISCUSSION...UPDATED 03...

DESPITE SUNSET HAVE SEEN ONLY A SLIGHT DOWNWARD BUILDING OF CIGS
THIS EVENING AND IN FACT...CIGS HAVE BEEN COMING UP NEAR THE
CENTER OF THE LOW OVER EASTERN IOWA MOVING INTO NORTHWEST
ILLINOIS. CONFIDENCE REMAINS LOW ON EXACT CIG TRENDS...BUT GIVEN
ONLY VERY SPOTTY LIFR CIGS THUS FAR AND LACK OF ANY SIGNIFICANT
LOWERING NOTED IN THE REGION HAVE RAISED FORECAST CIGS OVERNIGHT
BY A COUPLE HUNDRED FEET. A COUPLE BANDS OF SHOWERS WILL PIVOT
THROUGH THE AREA OVERNIGHT INTO EARLY TUES MORNING AND COULD HELP
BRIEFLY SCATTER OUT THE IFR CIGS FOR BRIEF PERIODS OF MVFR.

IZZI

UPDATED 00Z...

SLOW MOVING LOW PRESSURE SYSTEM WILL CONTINUE TO MOVE ACROSS THE
REGION THROUGH THE TAF CYCLE. RECENT IMPROVEMENT TO LOW END MVFR
EXPECTED TO BE TEMPORARY WITH CIGS LIKELY TO DROP BACK TO IFR VERY
NEAR THE 00Z TAF START TIME. WITH DECREASING WINDS AND MOIST LOW
LEVELS WOULD ANTICIPATE CIGS CONTINUING TO BUILD DOWNWARD TO LIFR
LATER THIS EVENING OR OVERNIGHT...THEN LIKELY STAYING THERE INTO
TUESDAY MORNING. WINDS WILL BECOME NORTHWEST AND BEGIN TO INCREASE
MID-LATE TUESDAY MORNING WHICH SHOULD BEGIN THE PROCESS OF
SCOURING OUT THE VERY LOW CIGS WITH IMPROVEMENT TO MVFR LIKELY
TUESDAY. LIKELY TO SEE MISTY/DRIZZLY CONDITIONS WITH THE LOW CIGS
TONIGHT INTO EARLY TUESDAY MORNING WITH AT LEAST OCNL SHOWERS
PIVOTING AROUND THE LOW BEFORE PRECIP CHANCES WANE TOWARD MIDDAY
TUESDAY.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW-MEDIUM CONFIDENCE IN CIGS
* MEDIUM CONFIDENCE IN PRECIP TRENDS
* FAIRLY HIGH CONFIDENCE IN GENERAL WIND TRENDS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

THURSDAY THROUGH SUNDAY...SOME PERIODIC MVFR CIGS POSSIBLE BUT
PRIMARILY VFR CONDITIONS EXPECTED.

IZZI

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIR MASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 152336
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
536 PM CST MON DEC 15 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJI-WHARA WITH THE FILLING SYSTEM
TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY PUSHING
SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY EVENING. OTHER
THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER AIR...NOT MUCH
EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR ABOVE OUR
SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER THROUGH TUESDAY
NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW MOIST LAYER LOOKS TO
EVENTUALLY DEVELOP HOLES IN THE CLOUDS WEDNESDAY. IN COLDER AIR
HIGHS WEDNESDAY EXPECTED FROM THE UPPER 20S TO LOWER 30S...OR A
LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIME FRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* IFR CIGS TO TREND TO LIFR TONIGHT AND LINGERING INTO TUESDAY
  MORNING BEFORE GRADUALLY IMPROVING TO MVFR DURING DAY TUESDAY

IZZI

//DISCUSSION...UPDATED 00Z...

SLOW MOVING LOW PRESSURE SYSTEM WILL CONTINUE TO MOVE ACROSS THE
REGION THROUGH THE TAF CYCLE. RECENT IMPROVEMENT TO LOW END MVFR
EXPECTED TO BE TEMPORARY WITH CIGS LIKELY TO DROP BACK TO IFR VERY
NEAR THE 00Z TAF START TIME. WITH DECREASING WINDS AND MOIST LOW
LEVELS WOULD ANTICIPATE CIGS CONTINUING TO BUILD DOWNWARD TO LIFR
LATER THIS EVENING OR OVERNIGHT...THEN LIKELY STAYING THERE INTO
TUESDAY MORNING. WINDS WILL BECOME NORTHWEST AND BEGIN TO INCREASE
MID-LATE TUESDAY MORNING WHICH SHOULD BEGIN THE PROCESS OF
SCOURING OUT THE VERY LOW CIGS WITH IMPROVEMENT TO MVFR LIKELY
TUESDAY. LIKELY TO SEE MISTY/DRIZZLY CONDITIONS WITH THE LOW CIGS
TONIGHT INTO EARLY TUESDAY MORNING WITH AT LEAST OCNL SHOWERS
PIVOTING AROUND THE LOW BEFORE PRECIP CHANCES WANE TOWARD MIDDAY
TUESDAY.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM-HIGH CONFIDENCE IN GENERAL CIG/VSBY TRENDS DOWNWARD
  TONIGHT THEN GRADUALLY IMPROVING TUESDAY...LOW CONFIDENCE IN
  PRECISE DETAILS OF HOW LOW TONIGHT AND HOW FAST UP TUESDAY
* MEDIUM CONFIDENCE IN PRECIP TRENDS
* FAIRLY HIGH CONFIDENCE IN GENERAL WIND TRENDS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

THURSDAY THROUGH SUNDAY...SOME PERIODIC MVFR CIGS POSSIBLE BUT
PRIMARILY VFR CONDITIONS EXPECTED.

IZZI

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIR MASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 152336
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
536 PM CST MON DEC 15 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJI-WHARA WITH THE FILLING SYSTEM
TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY PUSHING
SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY EVENING. OTHER
THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER AIR...NOT MUCH
EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR ABOVE OUR
SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER THROUGH TUESDAY
NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW MOIST LAYER LOOKS TO
EVENTUALLY DEVELOP HOLES IN THE CLOUDS WEDNESDAY. IN COLDER AIR
HIGHS WEDNESDAY EXPECTED FROM THE UPPER 20S TO LOWER 30S...OR A
LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIME FRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* IFR CIGS TO TREND TO LIFR TONIGHT AND LINGERING INTO TUESDAY
  MORNING BEFORE GRADUALLY IMPROVING TO MVFR DURING DAY TUESDAY

IZZI

//DISCUSSION...UPDATED 00Z...

SLOW MOVING LOW PRESSURE SYSTEM WILL CONTINUE TO MOVE ACROSS THE
REGION THROUGH THE TAF CYCLE. RECENT IMPROVEMENT TO LOW END MVFR
EXPECTED TO BE TEMPORARY WITH CIGS LIKELY TO DROP BACK TO IFR VERY
NEAR THE 00Z TAF START TIME. WITH DECREASING WINDS AND MOIST LOW
LEVELS WOULD ANTICIPATE CIGS CONTINUING TO BUILD DOWNWARD TO LIFR
LATER THIS EVENING OR OVERNIGHT...THEN LIKELY STAYING THERE INTO
TUESDAY MORNING. WINDS WILL BECOME NORTHWEST AND BEGIN TO INCREASE
MID-LATE TUESDAY MORNING WHICH SHOULD BEGIN THE PROCESS OF
SCOURING OUT THE VERY LOW CIGS WITH IMPROVEMENT TO MVFR LIKELY
TUESDAY. LIKELY TO SEE MISTY/DRIZZLY CONDITIONS WITH THE LOW CIGS
TONIGHT INTO EARLY TUESDAY MORNING WITH AT LEAST OCNL SHOWERS
PIVOTING AROUND THE LOW BEFORE PRECIP CHANCES WANE TOWARD MIDDAY
TUESDAY.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM-HIGH CONFIDENCE IN GENERAL CIG/VSBY TRENDS DOWNWARD
  TONIGHT THEN GRADUALLY IMPROVING TUESDAY...LOW CONFIDENCE IN
  PRECISE DETAILS OF HOW LOW TONIGHT AND HOW FAST UP TUESDAY
* MEDIUM CONFIDENCE IN PRECIP TRENDS
* FAIRLY HIGH CONFIDENCE IN GENERAL WIND TRENDS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

THURSDAY THROUGH SUNDAY...SOME PERIODIC MVFR CIGS POSSIBLE BUT
PRIMARILY VFR CONDITIONS EXPECTED.

IZZI

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIR MASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 152217
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
417 PM CST MON DEC 15 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJI-WARA WITH THE FILLING SYSTEM
TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY PUSHING
SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY EVENING. OTHER
THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER AIR...NOT MUCH
EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR ABOVE OUR
SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER THROUGH TUESDAY
NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW MOIST LAYER LOOKS TO
EVENTUALLY DEVELOP HOLES IN THE CLOUDS WEDNESDAY. IN COLDER AIR
HIGHS WEDNESDAY EXPECTED FROM THE UPPER 20S TO LOWER 30S...OR A
LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIMEFRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* IFR CEILINGS...LOWERING TO LIFR THIS EVENING.

* MVFR VIS LOWERING TO IFR TONIGHT...WITH PERIODS OF IFR POSSIBLE
  THIS AFTERNOON.

* SHOWERS MOVING THIS AFTERNOON...WITH SHOWERS OR DRIZZLE POSSIBLE
  THROUGH TUESDAY MORNING.

* SOUTHEAST WINDS...SHIFTING TO THE SOUTH/SOUTHWEST LATE
  TONIGHT...THEN BECOMING WEST/NORTHWEST TUESDAY MORNING.

IZZI

//DISCUSSION...UPDATED 18Z...

LOW CEILINGS AND REDUCED VIS IN FOG/DRIZZLE/SHOWERS CONTINUING
EARLY THIS AFTERNOON AS MOIST CONDITIONS MOVE OUT AHEAD OF LOW
PRESSURE TO THE WEST. SOME SLIGHT IMPROVEMENT HAS OCCURRED TODAY
MAINLY IN VIS WITH THE TERMINALS STILL HOLDING AROUND 3
MILES...BUT WHILE IFR/LIFR CEILINGS REMAIN. NOT OVERLY OPTIMISTIC
WITH OVERALL IMPROVEMENT WITH CEILINGS THE REST OF THIS
AFTERNOON...AND AM KEEPING ALL TERMINALS IFR FOR THE REMAINDER OF
THE DAY. PRECIP AXIS TO THE WEST WILL SLOWLY SHIFT FURTHER EAST
THIS AFTERNOON WITH AN INITIAL WAVE OF SHOWERY ACTIVITY EXPECTED
THROUGH EARLY EVENING. AS THE SYSTEM CONTINUES TO MOVE CLOSER TO
TO THE TERMINALS THIS EVENING DO THINK SHOWERS WILL LINGER BUT
LIKELY BECOME MIXED WITH MORE DRIZZLE ACTIVITY INTO THE OVERNIGHT
HOURS. AS THE SURFACE LOW MOVES OVERHEAD TONIGHT...CEILINGS WILL
QUICKLY FALL BACK TO LIFR THIS EVENING. BRING 300FT CEILINGS BACK
OVERHEAD TONIGHT...BUT WOULD NOT BE SURPRISED TO SEE PREVAILING
CEILINGS UNDER THIS HEIGHT FOR A PERIOD INTO EARLY TUESDAY
MORNING. FEEL CONFIDENT WITH VIS REDUCING ONCE AGAIN TONIGHT UNDER
THESE VERY MOIST CONDITIONS...BUT NOT OVERLY CONFIDENT WITH VIS
TRENDS/DURATION. WILL LIKELY OBSERVE VIS LOWER THAN FORECAST
TONIGHT AND EARLY TUESDAY MORNING...BUT THE LACK OF CONFIDENCE OF
TRENDS AND DURATION IS WHAT LIMITS MENTION OF LOWER VIS...NOT THE
ACTUAL OCCURRENCE.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM-HIGH CONFIDENCE ON GENERAL CIG TRENDING BACK DOWN TO IFR
  AND PROBABLY LIFR TONIGHT

* HIGH CONFIDENCE OF SHOWERS/DRIZZLE THIS AFTERNOON AND TONIGHT

* MEDIUM-HIGH CONFIDENCE WITH WIND SPEED/DIRECTION

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIRMASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 152117
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
317 PM CST MON DEC 15 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJI-WARA WITH THE FILLING SYSTEM
TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY PUSHING
SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY EVENING. OTHER
THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER AIR...NOT MUCH
EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR ABOVE OUR
SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER THROUGH TUESDAY
NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW MOIST LAYER LOOKS TO
EVENTUALLY DEVELOP HOLES IN THE CLOUDS WEDNESDAY. IN COLDER AIR
HIGHS WEDNESDAY EXPECTED FROM THE UPPER 20S TO LOWER 30S...OR A
LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIMEFRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* IFR CEILINGS...LOWERING TO LIFR THIS EVENING.

* MVFR VIS LOWERING TO IFR TONIGHT...WITH PERIODS OF IFR POSSIBLE
  THIS AFTERNOON.

* SHOWERS MOVING THIS AFTERNOON...WITH SHOWERS OR DRIZZLE POSSIBLE
  THROUGH TUESDAY MORNING.

* SOUTHEAST WINDS...SHIFTING TO THE SOUTH/SOUTHWEST LATE
  TONIGHT...THEN BECOMING WEST/NORTHWEST TUESDAY MORNING.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

LOW CEILINGS AND REDUCED VIS IN FOG/DRIZZLE/SHOWERS CONTINUING
EARLY THIS AFTERNOON AS MOIST CONDITIONS MOVE OUT AHEAD OF LOW
PRESSURE TO THE WEST. SOME SLIGHT IMPROVEMENT HAS OCCURRED TODAY
MAINLY IN VIS WITH THE TERMINALS STILL HOLDING AROUND 3
MILES...BUT WHILE IFR/LIFR CEILINGS REMAIN. NOT OVERLY OPTIMISTIC
WITH OVERALL IMPROVEMENT WITH CEILINGS THE REST OF THIS
AFTERNOON...AND AM KEEPING ALL TERMINALS IFR FOR THE REMAINDER OF
THE DAY. PRECIP AXIS TO THE WEST WILL SLOWLY SHIFT FURTHER EAST
THIS AFTERNOON WITH AN INITIAL WAVE OF SHOWERY ACTIVITY EXPECTED
THROUGH EARLY EVENING. AS THE SYSTEM CONTINUES TO MOVE CLOSER TO
TO THE TERMINALS THIS EVENING DO THINK SHOWERS WILL LINGER BUT
LIKELY BECOME MIXED WITH MORE DRIZZLE ACTIVITY INTO THE OVERNIGHT
HOURS. AS THE SURFACE LOW MOVES OVERHEAD TONIGHT...CEILINGS WILL
QUICKLY FALL BACK TO LIFR THIS EVENING. BRING 300FT CEILINGS BACK
OVERHEAD TONIGHT...BUT WOULD NOT BE SURPRISED TO SEE PREVAILING
CEILINGS UNDER THIS HEIGHT FOR A PERIOD INTO EARLY TUESDAY
MORNING. FEEL CONFIDENT WITH VIS REDUCING ONCE AGAIN TONIGHT UNDER
THESE VERY MOIST CONDITIONS...BUT NOT OVERLY CONFIDENT WITH VIS
TRENDS/DURATION. WILL LIKELY OBSERVE VIS LOWER THAN FORECAST
TONIGHT AND EARLY TUESDAY MORNING...BUT THE LACK OF CONFIDENCE OF
TRENDS AND DURATION IS WHAT LIMITS MENTION OF LOWER VIS...NOT THE
ACTUAL OCCURRENCE.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE OF IFR AND LIFR CEILINGS...MEDIUM HIGH
  CONFIDENCE OF EXACT TIMING AND DURATION.

* MEDIUM HIGH CONFIDENCE WITH VIS/TRENDS.

* HIGH CONFIDENCE OF SHOWERS/DRIZZLE THIS AFTERNOON AND TONIGHT.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIRMASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 152117
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
317 PM CST MON DEC 15 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJI-WARA WITH THE FILLING SYSTEM
TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY PUSHING
SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY EVENING. OTHER
THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER AIR...NOT MUCH
EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR ABOVE OUR
SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER THROUGH TUESDAY
NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW MOIST LAYER LOOKS TO
EVENTUALLY DEVELOP HOLES IN THE CLOUDS WEDNESDAY. IN COLDER AIR
HIGHS WEDNESDAY EXPECTED FROM THE UPPER 20S TO LOWER 30S...OR A
LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIMEFRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* IFR CEILINGS...LOWERING TO LIFR THIS EVENING.

* MVFR VIS LOWERING TO IFR TONIGHT...WITH PERIODS OF IFR POSSIBLE
  THIS AFTERNOON.

* SHOWERS MOVING THIS AFTERNOON...WITH SHOWERS OR DRIZZLE POSSIBLE
  THROUGH TUESDAY MORNING.

* SOUTHEAST WINDS...SHIFTING TO THE SOUTH/SOUTHWEST LATE
  TONIGHT...THEN BECOMING WEST/NORTHWEST TUESDAY MORNING.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

LOW CEILINGS AND REDUCED VIS IN FOG/DRIZZLE/SHOWERS CONTINUING
EARLY THIS AFTERNOON AS MOIST CONDITIONS MOVE OUT AHEAD OF LOW
PRESSURE TO THE WEST. SOME SLIGHT IMPROVEMENT HAS OCCURRED TODAY
MAINLY IN VIS WITH THE TERMINALS STILL HOLDING AROUND 3
MILES...BUT WHILE IFR/LIFR CEILINGS REMAIN. NOT OVERLY OPTIMISTIC
WITH OVERALL IMPROVEMENT WITH CEILINGS THE REST OF THIS
AFTERNOON...AND AM KEEPING ALL TERMINALS IFR FOR THE REMAINDER OF
THE DAY. PRECIP AXIS TO THE WEST WILL SLOWLY SHIFT FURTHER EAST
THIS AFTERNOON WITH AN INITIAL WAVE OF SHOWERY ACTIVITY EXPECTED
THROUGH EARLY EVENING. AS THE SYSTEM CONTINUES TO MOVE CLOSER TO
TO THE TERMINALS THIS EVENING DO THINK SHOWERS WILL LINGER BUT
LIKELY BECOME MIXED WITH MORE DRIZZLE ACTIVITY INTO THE OVERNIGHT
HOURS. AS THE SURFACE LOW MOVES OVERHEAD TONIGHT...CEILINGS WILL
QUICKLY FALL BACK TO LIFR THIS EVENING. BRING 300FT CEILINGS BACK
OVERHEAD TONIGHT...BUT WOULD NOT BE SURPRISED TO SEE PREVAILING
CEILINGS UNDER THIS HEIGHT FOR A PERIOD INTO EARLY TUESDAY
MORNING. FEEL CONFIDENT WITH VIS REDUCING ONCE AGAIN TONIGHT UNDER
THESE VERY MOIST CONDITIONS...BUT NOT OVERLY CONFIDENT WITH VIS
TRENDS/DURATION. WILL LIKELY OBSERVE VIS LOWER THAN FORECAST
TONIGHT AND EARLY TUESDAY MORNING...BUT THE LACK OF CONFIDENCE OF
TRENDS AND DURATION IS WHAT LIMITS MENTION OF LOWER VIS...NOT THE
ACTUAL OCCURRENCE.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE OF IFR AND LIFR CEILINGS...MEDIUM HIGH
  CONFIDENCE OF EXACT TIMING AND DURATION.

* MEDIUM HIGH CONFIDENCE WITH VIS/TRENDS.

* HIGH CONFIDENCE OF SHOWERS/DRIZZLE THIS AFTERNOON AND TONIGHT.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIRMASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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000
FXUS63 KLOT 152117
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
317 PM CST MON DEC 15 2014

.SHORT TERM...
315 PM CST

THROUGH WEDNESDAY...

TONIGHT THROUGH WEDNESDAY...

OCCLUDED SURFACE LOW PRESSURE WAS ANALYZED ALONG THE IOWA/MISSOURI
BORDER NEAR LAMONI IOWA AT 20Z...WITH MID-LEVEL CIRCULATION
APPROPRIATELY STACKED ABOVE IT PER GOES VAPOR IMAGERY. THIS SYSTEM
WILL CONTINUE TO MOVE SLOWLY TO THE EAST-NORTHEAST ACROSS THE
FORECAST AREA TONIGHT AND EARLY TUESDAY...BEFORE PASSING OFF TO THE
EAST AND FILLING DURING THE MIDDAY AND AFTERNOON HOURS. THE LOW
LEVEL MOISTURE AXIS AHEAD OF THE OCCLUDED SYSTEM STRETCHED NORTH
FROM THE LOWER MISSISSIPPI VALLEY INTO MO/IA...AND WILL SHIFT ACROSS
IL/IN TONIGHT AS THE LOW DRIFTS EAST. THE INITIAL RAIN BAND...WHICH
HAS BEEN FAIRLY WELL HANDLED BY GUIDANCE...WAS LIFTING NORTHEAST
ACROSS THE CWA THIS AFTERNOON. CONTINUED DRIZZLE AND PERIODS OF
LIGHT RAIN CAN BE EXPECTED THROUGH MORNING AS THE LOW MOVES ACROSS
THE CWA...ALONG WITH LOW CLOUDS AND AREAS OF FOG. LOCALIZED DENSE
FOG IS POSSIBLE...WITH SMALL TEMP-DEW POINT SPREADS AND PRECIP...
ESPECIALLY AS WINDS DIMINISH NEAR THE LOW CENTER. VISIBILITY OF
LESS THAN A MILE HAVE BEEN FAIRLY LIMITED SO FAR WITH NO PLANS FOR
ADVISORY AT THIS TIME...THOUGH WILL HAVE TO MONITOR EXTENT OF DENSE
FOG THIS EVENING/OVERNIGHT. TEMPERATURES AND DEW POINTS IN THE 40S
WITHIN THE OCCLUDED FRONTAL ZONE WILL MAKE FOR ANOTHER RELATIVELY
MILD NIGHT WITH LITTLE FALL-OFF EXPECTED.

THIS WILL CHANGE AS THE LOW MOVES EAST OF THE AREA TUESDAY...AND A
SECONDARY STRONGER COLD FRONT MOVES THROUGH. HIGH TEMPERATURES IN
THE LOW-MID 40S WILL COME EARLY IN THE MORNING FOR WESTERN PARTS OF
THE CWA...AND DURING THE MORNING IN THE EAST BEFORE GUSTY NORTHWEST
WINDS SEND TEMPS FALLING INTO THE 30S THROUGH THE AFTERNOON. LIGHT
PRECIP SHOULD BECOME MORE SHOWERY AND SPOTTY THROUGH THE DAY... AND
SHOULD BECOME A RAIN/SNOW MIX FROM THE WEST AS THE COLUMN COOLS.
FORECAST SOUNDINGS DO DEPICT DRYING IN THE MID-LEVELS WHICH WOULD
LOWER POTENTIAL FOR ICE CRYSTALS/SNOW PRODUCTION...MAKING A CHANGE
TO ALL SNOW UNLIKELY FOR ANY DURATION AND THUS NO ACCUMULATION
EXPECTED AND TEMPERATURES LOOK TO HOLD JUST ABOVE FREEZING UNTIL
PRECIP ENDS. SOME POTENTIAL FOR A FEW LAKE-INDUCED SNOW SHOWERS INTO
NORTHEAST PORTER COUNTY LATER TUESDAY NIGHT...THOUGH SHALLOW DEPTH
OF COLD AIR RESULTS IN MEAGER INVERSION/EQUILIBRIUM HEIGHTS WHICH
ARGUE AGAINST ANY SIGNIFICANT SNOW OR ACCUMULATION. AFTER MORNING
HIGHS IN THE 40S...AND TEMPS FALLING THROUGH THE 30S DURING THE
DAY/AFTERNOON...LOWS TUESDAY NIGHT SHOULD FALL INTO THE 20S AS GUSTY
WINDS MAINTAIN COLD ADVECTION.

ANOTHER SHORT WAVE CURRENTLY OVER SOUTHERN MANITOBA AND NORTHWESTERN
ONTARIO WILL DIG SOUTH AND SORT OF FUJI-WARA WITH THE FILLING SYSTEM
TO OUR EAST TUESDAY NIGHT AND WEDNESDAY...EVENTUALLY PUSHING
SOUTHEAST ACROSS THE AREA LATE WEDNESDAY OR WEDNESDAY EVENING. OTHER
THAN PRODUCING A LITTLE REINFORCING PUSH OF COLDER AIR...NOT MUCH
EXPECTED FROM THIS WAVE WITH AFOREMENTIONED DRY AIR ABOVE OUR
SHALLOW BOUNDARY LAYER. LOW CLOUDS MAY WELL LINGER THROUGH TUESDAY
NIGHT AND INTO EARLY WEDNESDAY...THOUGH SHALLOW MOIST LAYER LOOKS TO
EVENTUALLY DEVELOP HOLES IN THE CLOUDS WEDNESDAY. IN COLDER AIR
HIGHS WEDNESDAY EXPECTED FROM THE UPPER 20S TO LOWER 30S...OR A
LITTLE BELOW AVERAGE FOR MID-DECEMBER.

RATZER

&&

.LONG TERM...
315 PM CST

WEDNESDAY NIGHT THROUGH TUESDAY...

THURSDAY THROUGH MONDAY...

DRY BUT COOLER THAN AVERAGE CONDITIONS ANTICIPATED WEDNESDAY NIGHT
THROUGH FRIDAY AS UPPER TROUGH MOVES OFF TO THE EAST AND EVENTUALLY
ALLOWS SURFACE HIGH PRESSURE RIDGE TO SPREAD INTO THE REGION BY
FRIDAY. CONTINUING TO MONITOR UPPER TROUGH WHICH MOVES OUT OF THE
SOUTHWESTERN CONUS/NORTHERN MEXICO FRIDAY-SATURDAY...WITH MODELS
DEPICTING SOME DIFFERENCES IN PHASING NORTHERN AND SOUTHERN STREAM
JET ENERGY THAT CULMINATE IN DIFFERENCES IN AMPLIFICATION AND TRACK
TO SOME DEGREE OVER THE WEEKEND. OPERATIONAL GFS WHICH HAD BEEN A
NORTHERN OUTLIER ALONG WITH A FEW GEFS ENSEMBLE MEMBERS...HAS COME
INTO BETTER AGREEMENT WITH THE GEFS ENSEMBLE MEAN...ECMWF AND
PARALLEL 13 KM GFS RUNS IN MAINTAINING A FARTHER SOUTH TRACK WITH
THIS SYSTEM AND A SURFACE LOW WHICH PROPAGATES FROM THE GULF COAST
TO THE MID-ATLANTIC COAST. MUCH OF THE GUIDANCE KEEPS ANY ASSOCIATED
PRECIP SOUTH OF OUR CWA...THOUGH THE LESS AMPLIFIED GFS DOES SNEAK A
LITTLE LIGHT QPF ACROSS OUR FAR SOUTHEAST FRIDAY NIGHT INTO
SATURDAY. WHILE THE EARLY TRENDS SIGNAL NOT MUCH TO CONCERN
OURSELVES ABOUT...THE CULPRIT TROUGHS ARE STILL OUT OVER THE PACIFIC
AND DETAILS WILL MOST LIKELY CHANGE AS THE TIME DRAWS CLOSER. HAVE
CONTINUED A SLIGHT CHANCE POP MENTION ACROSS THE SOUTHEAST 1/3 OF
THE CWA FOR NOW. OTHERWISE...HIGH PRESSURE LOOKS TO MOVE IN LATER
IN THE SUNDAY-MONDAY TIMEFRAME.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* IFR CEILINGS...LOWERING TO LIFR THIS EVENING.

* MVFR VIS LOWERING TO IFR TONIGHT...WITH PERIODS OF IFR POSSIBLE
  THIS AFTERNOON.

* SHOWERS MOVING THIS AFTERNOON...WITH SHOWERS OR DRIZZLE POSSIBLE
  THROUGH TUESDAY MORNING.

* SOUTHEAST WINDS...SHIFTING TO THE SOUTH/SOUTHWEST LATE
  TONIGHT...THEN BECOMING WEST/NORTHWEST TUESDAY MORNING.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

LOW CEILINGS AND REDUCED VIS IN FOG/DRIZZLE/SHOWERS CONTINUING
EARLY THIS AFTERNOON AS MOIST CONDITIONS MOVE OUT AHEAD OF LOW
PRESSURE TO THE WEST. SOME SLIGHT IMPROVEMENT HAS OCCURRED TODAY
MAINLY IN VIS WITH THE TERMINALS STILL HOLDING AROUND 3
MILES...BUT WHILE IFR/LIFR CEILINGS REMAIN. NOT OVERLY OPTIMISTIC
WITH OVERALL IMPROVEMENT WITH CEILINGS THE REST OF THIS
AFTERNOON...AND AM KEEPING ALL TERMINALS IFR FOR THE REMAINDER OF
THE DAY. PRECIP AXIS TO THE WEST WILL SLOWLY SHIFT FURTHER EAST
THIS AFTERNOON WITH AN INITIAL WAVE OF SHOWERY ACTIVITY EXPECTED
THROUGH EARLY EVENING. AS THE SYSTEM CONTINUES TO MOVE CLOSER TO
TO THE TERMINALS THIS EVENING DO THINK SHOWERS WILL LINGER BUT
LIKELY BECOME MIXED WITH MORE DRIZZLE ACTIVITY INTO THE OVERNIGHT
HOURS. AS THE SURFACE LOW MOVES OVERHEAD TONIGHT...CEILINGS WILL
QUICKLY FALL BACK TO LIFR THIS EVENING. BRING 300FT CEILINGS BACK
OVERHEAD TONIGHT...BUT WOULD NOT BE SURPRISED TO SEE PREVAILING
CEILINGS UNDER THIS HEIGHT FOR A PERIOD INTO EARLY TUESDAY
MORNING. FEEL CONFIDENT WITH VIS REDUCING ONCE AGAIN TONIGHT UNDER
THESE VERY MOIST CONDITIONS...BUT NOT OVERLY CONFIDENT WITH VIS
TRENDS/DURATION. WILL LIKELY OBSERVE VIS LOWER THAN FORECAST
TONIGHT AND EARLY TUESDAY MORNING...BUT THE LACK OF CONFIDENCE OF
TRENDS AND DURATION IS WHAT LIMITS MENTION OF LOWER VIS...NOT THE
ACTUAL OCCURRENCE.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE OF IFR AND LIFR CEILINGS...MEDIUM HIGH
  CONFIDENCE OF EXACT TIMING AND DURATION.

* MEDIUM HIGH CONFIDENCE WITH VIS/TRENDS.

* HIGH CONFIDENCE OF SHOWERS/DRIZZLE THIS AFTERNOON AND TONIGHT.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIRMASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 7 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...1 PM
     TUESDAY TO 10 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 PM TUESDAY TO 10 AM
     THURSDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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000
FXUS63 KLOT 151959
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
159 PM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* IFR CEILINGS...LOWERING TO LIFR THIS EVENING.

* MVFR VIS LOWERING TO IFR TONIGHT...WITH PERIODS OF IFR POSSIBLE
  THIS AFTERNOON.

* SHOWERS MOVING THIS AFTERNOON...WITH SHOWERS OR DRIZZLE POSSIBLE
  THROUGH TUESDAY MORNING.

* SOUTHEAST WINDS...SHIFTING TO THE SOUTH/SOUTHWEST LATE
  TONIGHT...THEN BECOMING WEST/NORTHWEST TUESDAY MORNING.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

LOW CEILINGS AND REDUCED VIS IN FOG/DRIZZLE/SHOWERS CONTINUING
EARLY THIS AFTERNOON AS MOIST CONDITIONS MOVE OUT AHEAD OF LOW
PRESSURE TO THE WEST. SOME SLIGHT IMPROVEMENT HAS OCCURRED TODAY
MAINLY IN VIS WITH THE TERMINALS STILL HOLDING AROUND 3
MILES...BUT WHILE IFR/LIFR CEILINGS REMAIN. NOT OVERLY OPTIMISTIC
WITH OVERALL IMPROVEMENT WITH CEILINGS THE REST OF THIS
AFTERNOON...AND AM KEEPING ALL TERMINALS IFR FOR THE REMAINDER OF
THE DAY. PRECIP AXIS TO THE WEST WILL SLOWLY SHIFT FURTHER EAST
THIS AFTERNOON WITH AN INITIAL WAVE OF SHOWERY ACTIVITY EXPECTED
THROUGH EARLY EVENING. AS THE SYSTEM CONTINUES TO MOVE CLOSER TO
TO THE TERMINALS THIS EVENING DO THINK SHOWERS WILL LINGER BUT
LIKELY BECOME MIXED WITH MORE DRIZZLE ACTIVITY INTO THE OVERNIGHT
HOURS. AS THE SURFACE LOW MOVES OVERHEAD TONIGHT...CEILINGS WILL
QUICKLY FALL BACK TO LIFR THIS EVENING. BRING 300FT CEILINGS BACK
OVERHEAD TONIGHT...BUT WOULD NOT BE SURPRISED TO SEE PREVAILING
CEILINGS UNDER THIS HEIGHT FOR A PERIOD INTO EARLY TUESDAY
MORNING. FEEL CONFIDENT WITH VIS REDUCING ONCE AGAIN TONIGHT UNDER
THESE VERY MOIST CONDITIONS...BUT NOT OVERLY CONFIDENT WITH VIS
TRENDS/DURATION. WILL LIKELY OBSERVE VIS LOWER THAN FORECAST
TONIGHT AND EARLY TUESDAY MORNING...BUT THE LACK OF CONFIDENCE OF
TRENDS AND DURATION IS WHAT LIMITS MENTION OF LOWER VIS...NOT THE
ACTUAL OCCURRENCE.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE OF IFR AND LIFR CEILINGS...MEDIUM HIGH
  CONFIDENCE OF EXACT TIMING AND DURATION.

* MEDIUM HIGH CONFIDENCE WITH VIS/TRENDS.

* HIGH CONFIDENCE OF SHOWERS/DRIZZLE THIS AFTERNOON AND TONIGHT.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIRMASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 151959
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
159 PM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* IFR CEILINGS...LOWERING TO LIFR THIS EVENING.

* MVFR VIS LOWERING TO IFR TONIGHT...WITH PERIODS OF IFR POSSIBLE
  THIS AFTERNOON.

* SHOWERS MOVING THIS AFTERNOON...WITH SHOWERS OR DRIZZLE POSSIBLE
  THROUGH TUESDAY MORNING.

* SOUTHEAST WINDS...SHIFTING TO THE SOUTH/SOUTHWEST LATE
  TONIGHT...THEN BECOMING WEST/NORTHWEST TUESDAY MORNING.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

LOW CEILINGS AND REDUCED VIS IN FOG/DRIZZLE/SHOWERS CONTINUING
EARLY THIS AFTERNOON AS MOIST CONDITIONS MOVE OUT AHEAD OF LOW
PRESSURE TO THE WEST. SOME SLIGHT IMPROVEMENT HAS OCCURRED TODAY
MAINLY IN VIS WITH THE TERMINALS STILL HOLDING AROUND 3
MILES...BUT WHILE IFR/LIFR CEILINGS REMAIN. NOT OVERLY OPTIMISTIC
WITH OVERALL IMPROVEMENT WITH CEILINGS THE REST OF THIS
AFTERNOON...AND AM KEEPING ALL TERMINALS IFR FOR THE REMAINDER OF
THE DAY. PRECIP AXIS TO THE WEST WILL SLOWLY SHIFT FURTHER EAST
THIS AFTERNOON WITH AN INITIAL WAVE OF SHOWERY ACTIVITY EXPECTED
THROUGH EARLY EVENING. AS THE SYSTEM CONTINUES TO MOVE CLOSER TO
TO THE TERMINALS THIS EVENING DO THINK SHOWERS WILL LINGER BUT
LIKELY BECOME MIXED WITH MORE DRIZZLE ACTIVITY INTO THE OVERNIGHT
HOURS. AS THE SURFACE LOW MOVES OVERHEAD TONIGHT...CEILINGS WILL
QUICKLY FALL BACK TO LIFR THIS EVENING. BRING 300FT CEILINGS BACK
OVERHEAD TONIGHT...BUT WOULD NOT BE SURPRISED TO SEE PREVAILING
CEILINGS UNDER THIS HEIGHT FOR A PERIOD INTO EARLY TUESDAY
MORNING. FEEL CONFIDENT WITH VIS REDUCING ONCE AGAIN TONIGHT UNDER
THESE VERY MOIST CONDITIONS...BUT NOT OVERLY CONFIDENT WITH VIS
TRENDS/DURATION. WILL LIKELY OBSERVE VIS LOWER THAN FORECAST
TONIGHT AND EARLY TUESDAY MORNING...BUT THE LACK OF CONFIDENCE OF
TRENDS AND DURATION IS WHAT LIMITS MENTION OF LOWER VIS...NOT THE
ACTUAL OCCURRENCE.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE OF IFR AND LIFR CEILINGS...MEDIUM HIGH
  CONFIDENCE OF EXACT TIMING AND DURATION.

* MEDIUM HIGH CONFIDENCE WITH VIS/TRENDS.

* HIGH CONFIDENCE OF SHOWERS/DRIZZLE THIS AFTERNOON AND TONIGHT.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIRMASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 151951
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
151 PM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* IFR CEILINGS...LOWERING TO LIFR THIS EVENING.

* MVFR VIS LOWERING TO IFR TONIGHT.

* SHOWERS MOVING THIS AFTERNOON...WITH SHOWERS OR DRIZZLE POSSIBLE
  THROUGH TUESDAY MORNING.

* SOUTHEAST WINDS...SHIFTING TO THE SOUTH/SOUTHWEST LATE
  TONIGHT...THEN BECOMING WEST/NORTHWEST TUESDAY MORNING.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

LOW CEILINGS AND REDUCED VIS IN FOG/DRIZZLE/SHOWERS CONTINUING
EARLY THIS AFTERNOON AS MOIST CONDITIONS MOVE OUT AHEAD OF LOW
PRESSURE TO THE WEST. SOME SLIGHT IMPROVEMENT HAS OCCURRED TODAY
MAINLY IN VIS WITH THE TERMINALS STILL HOLDING AROUND 3
MILES...BUT WHILE IFR/LIFR CEILINGS REMAIN. NOT OVERLY OPTIMISTIC
WITH OVERALL IMPROVEMENT WITH CEILINGS THE REST OF THIS
AFTERNOON...AND AM KEEPING ALL TERMINALS IFR FOR THE REMAINDER OF
THE DAY. PRECIP AXIS TO THE WEST WILL SLOWLY SHIFT FURTHER EAST
THIS AFTERNOON WITH AN INITIAL WAVE OF SHOWERY ACTIVITY EXPECTED
THROUGH EARLY EVENING. AS THE SYSTEM CONTINUES TO MOVE CLOSER TO
TO THE TERMINALS THIS EVENING DO THINK SHOWERS WILL LINGER BUT
LIKELY BECOME MIXED WITH MORE DRIZZLE ACTIVITY INTO THE OVERNIGHT
HOURS. AS THE SURFACE LOW MOVES OVERHEAD TONIGHT...CEILINGS WILL
QUICKLY FALL BACK TO LIFR THIS EVENING. BRING 300FT CEILINGS BACK
OVERHEAD TONIGHT...BUT WOULD NOT BE SURPRISED TO SEE PREVAILING
CEILINGS UNDER THIS HEIGHT FOR A PERIOD INTO EARLY TUESDAY
MORNING. FEEL CONFIDENT WITH VIS REDUCING ONCE AGAIN TONIGHT UNDER
THESE VERY MOIST CONDITIONS...BUT NOT OVERLY CONFIDENT WITH VIS
TRENDS/DURATION. WILL LIKELY OBSERVE VIS LOWER THAN FORECAST
TONIGHT AND EARLY TUESDAY MORNING...BUT THE LACK OF CONFIDENCE OF
TRENDS AND DURATION IS WHAT LIMITS MENTION OF LOWER VIS...NOT THE
ACTUAL OCCURRENCE.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE OF IFR AND LIFR CEILINGS...MEDIUM HIGH
  CONFIDENCE OF EXACT TIMING AND DURATION.

* MEDIUM HIGH CONFIDENCE WITH VIS/TRENDS.

* HIGH CONFIDENCE OF SHOWERS/DRIZZLE THIS AFTERNOON AND TONIGHT.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIRMASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 151951
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
151 PM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* IFR CEILINGS...LOWERING TO LIFR THIS EVENING.

* MVFR VIS LOWERING TO IFR TONIGHT.

* SHOWERS MOVING THIS AFTERNOON...WITH SHOWERS OR DRIZZLE POSSIBLE
  THROUGH TUESDAY MORNING.

* SOUTHEAST WINDS...SHIFTING TO THE SOUTH/SOUTHWEST LATE
  TONIGHT...THEN BECOMING WEST/NORTHWEST TUESDAY MORNING.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

LOW CEILINGS AND REDUCED VIS IN FOG/DRIZZLE/SHOWERS CONTINUING
EARLY THIS AFTERNOON AS MOIST CONDITIONS MOVE OUT AHEAD OF LOW
PRESSURE TO THE WEST. SOME SLIGHT IMPROVEMENT HAS OCCURRED TODAY
MAINLY IN VIS WITH THE TERMINALS STILL HOLDING AROUND 3
MILES...BUT WHILE IFR/LIFR CEILINGS REMAIN. NOT OVERLY OPTIMISTIC
WITH OVERALL IMPROVEMENT WITH CEILINGS THE REST OF THIS
AFTERNOON...AND AM KEEPING ALL TERMINALS IFR FOR THE REMAINDER OF
THE DAY. PRECIP AXIS TO THE WEST WILL SLOWLY SHIFT FURTHER EAST
THIS AFTERNOON WITH AN INITIAL WAVE OF SHOWERY ACTIVITY EXPECTED
THROUGH EARLY EVENING. AS THE SYSTEM CONTINUES TO MOVE CLOSER TO
TO THE TERMINALS THIS EVENING DO THINK SHOWERS WILL LINGER BUT
LIKELY BECOME MIXED WITH MORE DRIZZLE ACTIVITY INTO THE OVERNIGHT
HOURS. AS THE SURFACE LOW MOVES OVERHEAD TONIGHT...CEILINGS WILL
QUICKLY FALL BACK TO LIFR THIS EVENING. BRING 300FT CEILINGS BACK
OVERHEAD TONIGHT...BUT WOULD NOT BE SURPRISED TO SEE PREVAILING
CEILINGS UNDER THIS HEIGHT FOR A PERIOD INTO EARLY TUESDAY
MORNING. FEEL CONFIDENT WITH VIS REDUCING ONCE AGAIN TONIGHT UNDER
THESE VERY MOIST CONDITIONS...BUT NOT OVERLY CONFIDENT WITH VIS
TRENDS/DURATION. WILL LIKELY OBSERVE VIS LOWER THAN FORECAST
TONIGHT AND EARLY TUESDAY MORNING...BUT THE LACK OF CONFIDENCE OF
TRENDS AND DURATION IS WHAT LIMITS MENTION OF LOWER VIS...NOT THE
ACTUAL OCCURRENCE.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE OF IFR AND LIFR CEILINGS...MEDIUM HIGH
  CONFIDENCE OF EXACT TIMING AND DURATION.

* MEDIUM HIGH CONFIDENCE WITH VIS/TRENDS.

* HIGH CONFIDENCE OF SHOWERS/DRIZZLE THIS AFTERNOON AND TONIGHT.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
150 PM CST

WITH HIGH PRESSURE OVER THE EASTERN SEABOARD AND LOW PRESSURE
DEEPENING OVER THE LOWER MISSOURI VALLEY...WARM...MOIST AIR HAS BEEN
DRAWN NORTH OVER THE RELATIVELY COOLER LAKE MICHIGAN
WATERS...ALLOWING FOR THE FORMATION OF DENSE FOG OVER THE
LAKE...ESPECIALLY OVER THE WESTERN PORTIONS OF THE LAKE.
ANTICIPATE THAT THERE WILL BE LITTLE CHANGE TO THE LAKE CONDITIONS
UNTIL A SIGNIFICANT AIRMASS CHANGE.  THIS CHANGE SHOULD OCCUR AFTER
THE SFC LOW PASSES ACROSS THE SRN TIP OF THE LAKE EARLY TUESDAY
MORNING AND WINDS BACK FROM SLY-SELY TO NLY-NWLY AND COOLER...DRIER
AIR IS DRAWN ACROSS THE LAKE.  WHILE THE LOW IS EXPECTED TO FILL AS
IT MOVES ACROSS LOWER MICHIGAN TO THE EASTERN GREAT LAKES TUESDAY
EVENING...HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY...SETTING UP A STRONG PRESSURE GRADIENT AS
WELL AS STRONG PRESSURE RISES OF AROUND 6-7MB PER 6 HOURS.  THIS
WILL LEAD TO STRENGTHENING WINDS...POSSIBLY REACHING GALE FORCE FOR
LATE TUESDAY EVENING INTO EARLY WEDNESDAY MORNING.  HOWEVER...WILL
NOT ISSUE A GALE WATCH/WARNING JUST YET AS A SCENARIO WITH A FILLING
LOW PASSING EAST OF THE LAKE WOULD BE LESS INCLINED TO CAUSE AN
INCREASE IN THE WIND FORECAST TO GALE FORCE THAN A FILLING LOW THAT
IS CURRENTLY BEING INDICATED BY THE FORECAST MODELS.  SO...WILL
INCLUDE THE CHANCE FOR GALE FORCE WINDS IN THE FORECAST WITH THE
CAVEAT THAT A GALE WARNING MAY BE NEEDED.  AS FOR THE NEARSHORE
WATERS...WILL GO WITH A SMALL CRAFT ADVISORY FOR ALL OF THE
NEARSHORE WATERS...BEGINNING EARLY TUESDAY AFTERNOON AS THE COOLER
AIR BEGINS TO FILTER OVER THE LAKE AND WINDS SET UP NWLY.  WAVE
SHOULD REMAIN HIGHER OVER THE INDIANA NEARSHORE WATERS MUCH LONGER
THAN THE ILLINOIS WATERS...SO WILL MAINTAIN THE SMALL CRAFT ADVISORY
FOR THE INDIANA NEARSHORE WATERS THROUGH LATE THURSDAY
MORNING...WHILE WINDS AND WAVES SHOULD DROP BELOW CRITERIA OVER THE
ILLINOIS WATERS BY LATE WEDNESDAY MORNING.  BRISK WNLY WINDS WILL
CONTINUE ACROSS THE LAKE INTO THURSDAY AFTERNOON AT WHICH POINT THE
HIGH PRESSURE BUILDING OUT OF THE NORTHERN PLAINS WILL SPREAD ACROSS
THE LAKE...ALLOWING WINDS TO DIMINISH.  HIGH PRESSURE WILL PERSIST
OVER THE GREAT LAKES REGION THROUGH THE WEEKEND KEEPING WINDS
RELATIVELY LIGHT AND NWLY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 151815
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1215 PM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* IFR CEILINGS...LOWERING TO LIFR THIS EVENING.

* MVFR VIS LOWERING TO IFR TONIGHT.

* SHOWERS MOVING THIS AFTERNOON...WITH SHOWERS OR DRIZZLE POSSIBLE
  THROUGH TUESDAY MORNING.

* SOUTHEAST WINDS...SHIFTING TO THE SOUTH/SOUTHWEST LATE
  TONIGHT...THEN BECOMING WEST/NORTHWEST TUESDAY MORNING.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

LOW CEILINGS AND REDUCED VIS IN FOG/DRIZZLE/SHOWERS CONTINUING
EARLY THIS AFTERNOON AS MOIST CONDITIONS MOVE OUT AHEAD OF LOW
PRESSURE TO THE WEST. SOME SLIGHT IMPROVEMENT HAS OCCURRED TODAY
MAINLY IN VIS WITH THE TERMINALS STILL HOLDING AROUND 3
MILES...BUT WHILE IFR/LIFR CEILINGS REMAIN. NOT OVERLY OPTIMISTIC
WITH OVERALL IMPROVEMENT WITH CEILINGS THE REST OF THIS
AFTERNOON...AND AM KEEPING ALL TERMINALS IFR FOR THE REMAINDER OF
THE DAY. PRECIP AXIS TO THE WEST WILL SLOWLY SHIFT FURTHER EAST
THIS AFTERNOON WITH AN INITIAL WAVE OF SHOWERY ACTIVITY EXPECTED
THROUGH EARLY EVENING. AS THE SYSTEM CONTINUES TO MOVE CLOSER TO
TO THE TERMINALS THIS EVENING DO THINK SHOWERS WILL LINGER BUT
LIKELY BECOME MIXED WITH MORE DRIZZLE ACTIVITY INTO THE OVERNIGHT
HOURS. AS THE SURFACE LOW MOVES OVERHEAD TONIGHT...CEILINGS WILL
QUICKLY FALL BACK TO LIFR THIS EVENING. BRING 300FT CEILINGS BACK
OVERHEAD TONIGHT...BUT WOULD NOT BE SURPRISED TO SEE PREVAILING
CEILINGS UNDER THIS HEIGHT FOR A PERIOD INTO EARLY TUESDAY
MORNING. FEEL CONFIDENT WITH VIS REDUCING ONCE AGAIN TONIGHT UNDER
THESE VERY MOIST CONDITIONS...BUT NOT OVERLY CONFIDENT WITH VIS
TRENDS/DURATION. WILL LIKELY OBSERVE VIS LOWER THAN FORECAST
TONIGHT AND EARLY TUESDAY MORNING...BUT THE LACK OF CONFIDENCE OF
TRENDS AND DURATION IS WHAT LIMITS MENTION OF LOWER VIS...NOT THE
ACTUAL OCCURRENCE.

RODRIGUEZ


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE OF IFR AND LIFR CEILINGS...MEDIUM HIGH
  CONFIDENCE OF EXACT TIMING AND DURATION.

* MEDIUM HIGH CONFIDENCE WITH VIS/TRENDS.

* HIGH CONFIDENCE OF SHOWERS/DRIZZLE THIS AFTERNOON AND TONIGHT.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
212 AM CST

SOUTH TO SOUTHEAST WINDS WILL PREVAIL OVER THE LAKE TODAY AND INTO
TONIGHT. ON THESE WINDS CONTINUED HIGH MOISTURE WILL STEER OVER THE
LAKE. WET BULB TEMPERATURE VALUES WELL IN EXCESS OF THE WATER
TEMPERATURES SHOULD CONTINUE FOG. WEB CAM IMAGERY FROM THE
CHICAGO CRIB ALONG WITH A SHIP OBSERVATION WEST OF MUSKEGON EARLY
THIS MORNING INDICATE THE PRESENCE OF DENSE FOG AND DO NOT SEE
THAT IMMEDIATELY DEPARTING. SO HAVE GONE WITH AN ADVISORY FOR THE
OPEN WATER AND NEARSHORE AREAS OF ILLINOIS AND INDIANA THROUGH
TODAY. ITS POSSIBLE SCATTERED SHOWERS THIS AFTERNOON...ALONG WITH
OFFSHORE FLOW...HELPS THE FOG TO EASE SOME IN THE ILLINOIS AND
INDIANA NEARSHORES...BUT CONFIDENCE ON THIS IS LOW.

LOW PRESSURE WILL MOVE ACROSS THE SOUTHERN PART OF THE LAKE TONIGHT
BRINGING A LULL IN THE WINDS...BUT AS THE LOW MOVES EAST DURING THE
DAY TUESDAY...NORTHWEST WINDS WILL QUICKLY RAMP UP. STILL EXPECTING
AN 18 TO MAYBE 24-HOUR PERIOD OR SO OF 30 KT WINDS OVER MUCH OF THE
OPEN WATER AS MODEL GUIDANCE IS IN GOOD CONSISTENT AGREEMENT WITH
THIS. HIGH PRESSURE WILL EVENTUALLY BUILD OVER THE LAKE ON
THURSDAY BUT WEAKENING AS IT DOES. LOW PRESSURE IS EXPECTED BOTH
NORTH AND SOUTH OF THE LAKE DURING THE FRIDAY/SATURDAY PERIOD. THE
FEATURE TO THE SOUTH IS EXPECTED TO HAVE MORE WIND INFLUENCE ON
THE LAKE...BRINGING NORTHEAST FLOW FOR A PERIOD DURING THAT TIME
FRAME.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 151815
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1215 PM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* IFR CEILINGS...LOWERING TO LIFR THIS EVENING.

* MVFR VIS LOWERING TO IFR TONIGHT.

* SHOWERS MOVING THIS AFTERNOON...WITH SHOWERS OR DRIZZLE POSSIBLE
  THROUGH TUESDAY MORNING.

* SOUTHEAST WINDS...SHIFTING TO THE SOUTH/SOUTHWEST LATE
  TONIGHT...THEN BECOMING WEST/NORTHWEST TUESDAY MORNING.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

LOW CEILINGS AND REDUCED VIS IN FOG/DRIZZLE/SHOWERS CONTINUING
EARLY THIS AFTERNOON AS MOIST CONDITIONS MOVE OUT AHEAD OF LOW
PRESSURE TO THE WEST. SOME SLIGHT IMPROVEMENT HAS OCCURRED TODAY
MAINLY IN VIS WITH THE TERMINALS STILL HOLDING AROUND 3
MILES...BUT WHILE IFR/LIFR CEILINGS REMAIN. NOT OVERLY OPTIMISTIC
WITH OVERALL IMPROVEMENT WITH CEILINGS THE REST OF THIS
AFTERNOON...AND AM KEEPING ALL TERMINALS IFR FOR THE REMAINDER OF
THE DAY. PRECIP AXIS TO THE WEST WILL SLOWLY SHIFT FURTHER EAST
THIS AFTERNOON WITH AN INITIAL WAVE OF SHOWERY ACTIVITY EXPECTED
THROUGH EARLY EVENING. AS THE SYSTEM CONTINUES TO MOVE CLOSER TO
TO THE TERMINALS THIS EVENING DO THINK SHOWERS WILL LINGER BUT
LIKELY BECOME MIXED WITH MORE DRIZZLE ACTIVITY INTO THE OVERNIGHT
HOURS. AS THE SURFACE LOW MOVES OVERHEAD TONIGHT...CEILINGS WILL
QUICKLY FALL BACK TO LIFR THIS EVENING. BRING 300FT CEILINGS BACK
OVERHEAD TONIGHT...BUT WOULD NOT BE SURPRISED TO SEE PREVAILING
CEILINGS UNDER THIS HEIGHT FOR A PERIOD INTO EARLY TUESDAY
MORNING. FEEL CONFIDENT WITH VIS REDUCING ONCE AGAIN TONIGHT UNDER
THESE VERY MOIST CONDITIONS...BUT NOT OVERLY CONFIDENT WITH VIS
TRENDS/DURATION. WILL LIKELY OBSERVE VIS LOWER THAN FORECAST
TONIGHT AND EARLY TUESDAY MORNING...BUT THE LACK OF CONFIDENCE OF
TRENDS AND DURATION IS WHAT LIMITS MENTION OF LOWER VIS...NOT THE
ACTUAL OCCURRENCE.

RODRIGUEZ


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE OF IFR AND LIFR CEILINGS...MEDIUM HIGH
  CONFIDENCE OF EXACT TIMING AND DURATION.

* MEDIUM HIGH CONFIDENCE WITH VIS/TRENDS.

* HIGH CONFIDENCE OF SHOWERS/DRIZZLE THIS AFTERNOON AND TONIGHT.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
212 AM CST

SOUTH TO SOUTHEAST WINDS WILL PREVAIL OVER THE LAKE TODAY AND INTO
TONIGHT. ON THESE WINDS CONTINUED HIGH MOISTURE WILL STEER OVER THE
LAKE. WET BULB TEMPERATURE VALUES WELL IN EXCESS OF THE WATER
TEMPERATURES SHOULD CONTINUE FOG. WEB CAM IMAGERY FROM THE
CHICAGO CRIB ALONG WITH A SHIP OBSERVATION WEST OF MUSKEGON EARLY
THIS MORNING INDICATE THE PRESENCE OF DENSE FOG AND DO NOT SEE
THAT IMMEDIATELY DEPARTING. SO HAVE GONE WITH AN ADVISORY FOR THE
OPEN WATER AND NEARSHORE AREAS OF ILLINOIS AND INDIANA THROUGH
TODAY. ITS POSSIBLE SCATTERED SHOWERS THIS AFTERNOON...ALONG WITH
OFFSHORE FLOW...HELPS THE FOG TO EASE SOME IN THE ILLINOIS AND
INDIANA NEARSHORES...BUT CONFIDENCE ON THIS IS LOW.

LOW PRESSURE WILL MOVE ACROSS THE SOUTHERN PART OF THE LAKE TONIGHT
BRINGING A LULL IN THE WINDS...BUT AS THE LOW MOVES EAST DURING THE
DAY TUESDAY...NORTHWEST WINDS WILL QUICKLY RAMP UP. STILL EXPECTING
AN 18 TO MAYBE 24-HOUR PERIOD OR SO OF 30 KT WINDS OVER MUCH OF THE
OPEN WATER AS MODEL GUIDANCE IS IN GOOD CONSISTENT AGREEMENT WITH
THIS. HIGH PRESSURE WILL EVENTUALLY BUILD OVER THE LAKE ON
THURSDAY BUT WEAKENING AS IT DOES. LOW PRESSURE IS EXPECTED BOTH
NORTH AND SOUTH OF THE LAKE DURING THE FRIDAY/SATURDAY PERIOD. THE
FEATURE TO THE SOUTH IS EXPECTED TO HAVE MORE WIND INFLUENCE ON
THE LAKE...BRINGING NORTHEAST FLOW FOR A PERIOD DURING THAT TIME
FRAME.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 151607
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1007 AM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* IFR CIGS SLIGHTLY IMPROVING THROUGH MID DAY.

* VISIBILITY GRADUALLY IMPROVING THIS MORNING.

* SOUTHEAST WINDS INCREASING TO 12-14KT BY EARLY AFTERNOON AND
  PERSISTING THROUGH EVENING.

* SHOWERS MOVING IN EARLY THIS AFTERNOON. SHOWER POTENTIAL PERSIST
  THROUGH REST OF TAF.

* RETURNING IFR OR LIFR CONDITIONS TONIGHT IN FOG/DRIZZLE.

RODRIGUEZ/MTF

//DISCUSSION...UPDATED 12Z...

SOUTHERLY FLOW AHEAD OF APPROACHING LOW PRESSURE CONTINUES OVER
THE AREA THIS MORNING. CIGS AND VISBYS HAVE SHOWN A SLIGHT
IMPROVING TREND AT A MAJORITY OF AREA AIRPORTS SINCE 10Z AND THAT
TREND WILL VERY GRADUALLY CONTINUE THROUGH 14Z-15Z BEFORE A
LIKELY MORE RAPID IMPROVEMENT. THE LOWEST VISBYS EARLY THIS
MORNING SEEM TO BE ASSOCIATED WITH BOTH DRIZZLE AND FOG...WITH
THE DRIZZLE NOW BEING PATCHY.

IT IS NOT IMPOSSIBLE THAT MDW STILL DROPS DOWN TO 200FT PRIOR TO
14Z...HOWEVER IT WOULD LIKELY NOW BE VERY TEMPORARY...AND SO
CONTINUE TAF ABOVE THAT.

THIS AFTERNOON THE SOUTH WINDS WILL BECOME MORE SOUTHEAST AND
INCREASE IN SPEED WITH THE APPROACHING LOW. IN ADDITION...AN ARC
OF SHOWERS THAT EXTENDS FROM SOUTHEAST IA THROUGH WESTERN IL AS OF
12Z WILL MOVE NORTHEAST OVER THE AREA. THE OVERALL COVERAGE LIKELY
WILL DISSIPATE SOME...BUT MOST AREAS SHOULD SEE SHOWERS DURING THE
EARLY TO MID AFTERNOON. WHAT THE CIGS AND VISBYS WILL DO
UNDERNEATH THESE SHOWERS IS DIFFICULT TO SAY GIVEN THE MOIST AIR
MASS AND ALREADY SOMEWHAT LOW VISBYS AND CIGS...BUT WOULD EXPECT
MAINLY MVFR/VFR.

BEHIND THE INITIAL ARC OF SHOWERS...OVERALL SUPPORT FOR SCATTERED
SHOWERS AND PATCHY DRIZZLE WILL CONTINUE. WITH THE LOW EXPECTED TO
MOVE DIRECTLY OVER THE AREA TONIGHT...CIGS AND VISBYS WILL ONCE
AGAIN COME DOWN AND THE LIKELIHOOD IS INCREASING THAT IT IS BACK
INTO THE LIFR CATEGORY. BEHIND THE LOW...WINDS WILL BECOME
NORTHWEST AND INCREASE IN SPEED INTO THE DAY TUESDAY.

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH IN CIG AND VISBY IMPROVEMENT...MEDIUM IN SPECIFIC TIMING
  AND EXTENT OF IMPROVEMENT ESPECIALLY WITH CIGS.

* HIGH IN WINDS.

* MEDIUM-HIGH IN SHOWERS DURING THE EARLY TO MID AFTERNOON. LOW IN
  WHAT CIGS AND VISBYS WILL BE DURING RAIN.

* HIGH IN RETURNING IFR TONIGHT. LOW ON HOW FAR CONDITIONS WILL
  DROP.

RODRIGUEZ/MTF

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
212 AM CST

SOUTH TO SOUTHEAST WINDS WILL PREVAIL OVER THE LAKE TODAY AND INTO
TONIGHT. ON THESE WINDS CONTINUED HIGH MOISTURE WILL STEER OVER THE
LAKE. WET BULB TEMPERATURE VALUES WELL IN EXCESS OF THE WATER
TEMPERATURES SHOULD CONTINUE FOG. WEB CAM IMAGERY FROM THE
CHICAGO CRIB ALONG WITH A SHIP OBSERVATION WEST OF MUSKEGON EARLY
THIS MORNING INDICATE THE PRESENCE OF DENSE FOG AND DO NOT SEE
THAT IMMEDIATELY DEPARTING. SO HAVE GONE WITH AN ADVISORY FOR THE
OPEN WATER AND NEARSHORE AREAS OF ILLINOIS AND INDIANA THROUGH
TODAY. ITS POSSIBLE SCATTERED SHOWERS THIS AFTERNOON...ALONG WITH
OFFSHORE FLOW...HELPS THE FOG TO EASE SOME IN THE ILLINOIS AND
INDIANA NEARSHORES...BUT CONFIDENCE ON THIS IS LOW.

LOW PRESSURE WILL MOVE ACROSS THE SOUTHERN PART OF THE LAKE TONIGHT
BRINGING A LULL IN THE WINDS...BUT AS THE LOW MOVES EAST DURING THE
DAY TUESDAY...NORTHWEST WINDS WILL QUICKLY RAMP UP. STILL EXPECTING
AN 18 TO MAYBE 24-HOUR PERIOD OR SO OF 30 KT WINDS OVER MUCH OF THE
OPEN WATER AS MODEL GUIDANCE IS IN GOOD CONSISTENT AGREEMENT WITH
THIS. HIGH PRESSURE WILL EVENTUALLY BUILD OVER THE LAKE ON
THURSDAY BUT WEAKENING AS IT DOES. LOW PRESSURE IS EXPECTED BOTH
NORTH AND SOUTH OF THE LAKE DURING THE FRIDAY/SATURDAY PERIOD. THE
FEATURE TO THE SOUTH IS EXPECTED TO HAVE MORE WIND INFLUENCE ON
THE LAKE...BRINGING NORTHEAST FLOW FOR A PERIOD DURING THAT TIME
FRAME.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 151607
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1007 AM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* IFR CIGS SLIGHTLY IMPROVING THROUGH MID DAY.

* VISIBILITY GRADUALLY IMPROVING THIS MORNING.

* SOUTHEAST WINDS INCREASING TO 12-14KT BY EARLY AFTERNOON AND
  PERSISTING THROUGH EVENING.

* SHOWERS MOVING IN EARLY THIS AFTERNOON. SHOWER POTENTIAL PERSIST
  THROUGH REST OF TAF.

* RETURNING IFR OR LIFR CONDITIONS TONIGHT IN FOG/DRIZZLE.

RODRIGUEZ/MTF

//DISCUSSION...UPDATED 12Z...

SOUTHERLY FLOW AHEAD OF APPROACHING LOW PRESSURE CONTINUES OVER
THE AREA THIS MORNING. CIGS AND VISBYS HAVE SHOWN A SLIGHT
IMPROVING TREND AT A MAJORITY OF AREA AIRPORTS SINCE 10Z AND THAT
TREND WILL VERY GRADUALLY CONTINUE THROUGH 14Z-15Z BEFORE A
LIKELY MORE RAPID IMPROVEMENT. THE LOWEST VISBYS EARLY THIS
MORNING SEEM TO BE ASSOCIATED WITH BOTH DRIZZLE AND FOG...WITH
THE DRIZZLE NOW BEING PATCHY.

IT IS NOT IMPOSSIBLE THAT MDW STILL DROPS DOWN TO 200FT PRIOR TO
14Z...HOWEVER IT WOULD LIKELY NOW BE VERY TEMPORARY...AND SO
CONTINUE TAF ABOVE THAT.

THIS AFTERNOON THE SOUTH WINDS WILL BECOME MORE SOUTHEAST AND
INCREASE IN SPEED WITH THE APPROACHING LOW. IN ADDITION...AN ARC
OF SHOWERS THAT EXTENDS FROM SOUTHEAST IA THROUGH WESTERN IL AS OF
12Z WILL MOVE NORTHEAST OVER THE AREA. THE OVERALL COVERAGE LIKELY
WILL DISSIPATE SOME...BUT MOST AREAS SHOULD SEE SHOWERS DURING THE
EARLY TO MID AFTERNOON. WHAT THE CIGS AND VISBYS WILL DO
UNDERNEATH THESE SHOWERS IS DIFFICULT TO SAY GIVEN THE MOIST AIR
MASS AND ALREADY SOMEWHAT LOW VISBYS AND CIGS...BUT WOULD EXPECT
MAINLY MVFR/VFR.

BEHIND THE INITIAL ARC OF SHOWERS...OVERALL SUPPORT FOR SCATTERED
SHOWERS AND PATCHY DRIZZLE WILL CONTINUE. WITH THE LOW EXPECTED TO
MOVE DIRECTLY OVER THE AREA TONIGHT...CIGS AND VISBYS WILL ONCE
AGAIN COME DOWN AND THE LIKELIHOOD IS INCREASING THAT IT IS BACK
INTO THE LIFR CATEGORY. BEHIND THE LOW...WINDS WILL BECOME
NORTHWEST AND INCREASE IN SPEED INTO THE DAY TUESDAY.

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH IN CIG AND VISBY IMPROVEMENT...MEDIUM IN SPECIFIC TIMING
  AND EXTENT OF IMPROVEMENT ESPECIALLY WITH CIGS.

* HIGH IN WINDS.

* MEDIUM-HIGH IN SHOWERS DURING THE EARLY TO MID AFTERNOON. LOW IN
  WHAT CIGS AND VISBYS WILL BE DURING RAIN.

* HIGH IN RETURNING IFR TONIGHT. LOW ON HOW FAR CONDITIONS WILL
  DROP.

RODRIGUEZ/MTF

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
212 AM CST

SOUTH TO SOUTHEAST WINDS WILL PREVAIL OVER THE LAKE TODAY AND INTO
TONIGHT. ON THESE WINDS CONTINUED HIGH MOISTURE WILL STEER OVER THE
LAKE. WET BULB TEMPERATURE VALUES WELL IN EXCESS OF THE WATER
TEMPERATURES SHOULD CONTINUE FOG. WEB CAM IMAGERY FROM THE
CHICAGO CRIB ALONG WITH A SHIP OBSERVATION WEST OF MUSKEGON EARLY
THIS MORNING INDICATE THE PRESENCE OF DENSE FOG AND DO NOT SEE
THAT IMMEDIATELY DEPARTING. SO HAVE GONE WITH AN ADVISORY FOR THE
OPEN WATER AND NEARSHORE AREAS OF ILLINOIS AND INDIANA THROUGH
TODAY. ITS POSSIBLE SCATTERED SHOWERS THIS AFTERNOON...ALONG WITH
OFFSHORE FLOW...HELPS THE FOG TO EASE SOME IN THE ILLINOIS AND
INDIANA NEARSHORES...BUT CONFIDENCE ON THIS IS LOW.

LOW PRESSURE WILL MOVE ACROSS THE SOUTHERN PART OF THE LAKE TONIGHT
BRINGING A LULL IN THE WINDS...BUT AS THE LOW MOVES EAST DURING THE
DAY TUESDAY...NORTHWEST WINDS WILL QUICKLY RAMP UP. STILL EXPECTING
AN 18 TO MAYBE 24-HOUR PERIOD OR SO OF 30 KT WINDS OVER MUCH OF THE
OPEN WATER AS MODEL GUIDANCE IS IN GOOD CONSISTENT AGREEMENT WITH
THIS. HIGH PRESSURE WILL EVENTUALLY BUILD OVER THE LAKE ON
THURSDAY BUT WEAKENING AS IT DOES. LOW PRESSURE IS EXPECTED BOTH
NORTH AND SOUTH OF THE LAKE DURING THE FRIDAY/SATURDAY PERIOD. THE
FEATURE TO THE SOUTH IS EXPECTED TO HAVE MORE WIND INFLUENCE ON
THE LAKE...BRINGING NORTHEAST FLOW FOR A PERIOD DURING THAT TIME
FRAME.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 151419
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
819 AM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* LIFR CIGS LIKELY THROUGH 16Z WITH MORE MARKED IMPROVEMENT BY MID
  DAY.

* VISIBILITY GRADUALLY IMPROVING THIS MORNING WITH FOG AND PATCHY
  DRIZZLE KEEPING THINGS IFR EARLY.

* SOUTH WINDS BECOMING SOUTHEASTERLY LATER THIS MORNING AND
  INCREASING TO 12-14KT BY EARLY AFTERNOON AND PERSISTING THROUGH
  EVENING.

* SHOWERS MOVING IN EARLY THIS AFTERNOON. SHOWER POTENTIAL PERSIST
  THROUGH REST OF TAF.

* RETURNING IFR OR LIFR CONDITIONS TONIGHT IN FOG/DRIZZLE.

RODRIGUEZ/MTF

//DISCUSSION...UPDATED 12Z...

SOUTHERLY FLOW AHEAD OF APPROACHING LOW PRESSURE CONTINUES OVER
THE AREA THIS MORNING. CIGS AND VISBYS HAVE SHOWN A SLIGHT
IMPROVING TREND AT A MAJORITY OF AREA AIRPORTS SINCE 10Z AND THAT
TREND WILL VERY GRADUALLY CONTINUE THROUGH 14Z-15Z BEFORE A
LIKELY MORE RAPID IMPROVEMENT. THE LOWEST VISBYS EARLY THIS
MORNING SEEM TO BE ASSOCIATED WITH BOTH DRIZZLE AND FOG...WITH
THE DRIZZLE NOW BEING PATCHY.

IT IS NOT IMPOSSIBLE THAT MDW STILL DROPS DOWN TO 200FT PRIOR TO
14Z...HOWEVER IT WOULD LIKELY NOW BE VERY TEMPORARY...AND SO
CONTINUE TAF ABOVE THAT.

THIS AFTERNOON THE SOUTH WINDS WILL BECOME MORE SOUTHEAST AND
INCREASE IN SPEED WITH THE APPROACHING LOW. IN ADDITION...AN ARC
OF SHOWERS THAT EXTENDS FROM SOUTHEAST IA THROUGH WESTERN IL AS OF
12Z WILL MOVE NORTHEAST OVER THE AREA. THE OVERALL COVERAGE LIKELY
WILL DISSIPATE SOME...BUT MOST AREAS SHOULD SEE SHOWERS DURING THE
EARLY TO MID AFTERNOON. WHAT THE CIGS AND VISBYS WILL DO
UNDERNEATH THESE SHOWERS IS DIFFICULT TO SAY GIVEN THE MOIST AIR
MASS AND ALREADY SOMEWHAT LOW VISBYS AND CIGS...BUT WOULD EXPECT
MAINLY MVFR/VFR.

BEHIND THE INITIAL ARC OF SHOWERS...OVERALL SUPPORT FOR SCATTERED
SHOWERS AND PATCHY DRIZZLE WILL CONTINUE. WITH THE LOW EXPECTED TO
MOVE DIRECTLY OVER THE AREA TONIGHT...CIGS AND VISBYS WILL ONCE
AGAIN COME DOWN AND THE LIKELIHOOD IS INCREASING THAT IT IS BACK
INTO THE LIFR CATEGORY. BEHIND THE LOW...WINDS WILL BECOME
NORTHWEST AND INCREASE IN SPEED INTO THE DAY TUESDAY.

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH IN CIG AND VISBY IMPROVEMENT...MEDIUM IN SPECIFIC TIMING
  AND EXTENT OF IMPROVEMENT.

* HIGH IN WINDS.

* MEDIUM-HIGH IN SHOWERS DURING THE EARLY TO MID AFTERNOON. LOW IN
  WHAT CIGS AND VISBYS WILL BE DURING RAIN.

* HIGH IN RETURNING IFR TONIGHT. LOW ON HOW FAR CONDITIONS WILL
  DROP.

RODRIGUEZ/MTF

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
212 AM CST

SOUTH TO SOUTHEAST WINDS WILL PREVAIL OVER THE LAKE TODAY AND INTO
TONIGHT. ON THESE WINDS CONTINUED HIGH MOISTURE WILL STEER OVER THE
LAKE. WET BULB TEMPERATURE VALUES WELL IN EXCESS OF THE WATER
TEMPERATURES SHOULD CONTINUE FOG. WEB CAM IMAGERY FROM THE
CHICAGO CRIB ALONG WITH A SHIP OBSERVATION WEST OF MUSKEGON EARLY
THIS MORNING INDICATE THE PRESENCE OF DENSE FOG AND DO NOT SEE
THAT IMMEDIATELY DEPARTING. SO HAVE GONE WITH AN ADVISORY FOR THE
OPEN WATER AND NEARSHORE AREAS OF ILLINOIS AND INDIANA THROUGH
TODAY. ITS POSSIBLE SCATTERED SHOWERS THIS AFTERNOON...ALONG WITH
OFFSHORE FLOW...HELPS THE FOG TO EASE SOME IN THE ILLINOIS AND
INDIANA NEARSHORES...BUT CONFIDENCE ON THIS IS LOW.

LOW PRESSURE WILL MOVE ACROSS THE SOUTHERN PART OF THE LAKE TONIGHT
BRINGING A LULL IN THE WINDS...BUT AS THE LOW MOVES EAST DURING THE
DAY TUESDAY...NORTHWEST WINDS WILL QUICKLY RAMP UP. STILL EXPECTING
AN 18 TO MAYBE 24-HOUR PERIOD OR SO OF 30 KT WINDS OVER MUCH OF THE
OPEN WATER AS MODEL GUIDANCE IS IN GOOD CONSISTENT AGREEMENT WITH
THIS. HIGH PRESSURE WILL EVENTUALLY BUILD OVER THE LAKE ON
THURSDAY BUT WEAKENING AS IT DOES. LOW PRESSURE IS EXPECTED BOTH
NORTH AND SOUTH OF THE LAKE DURING THE FRIDAY/SATURDAY PERIOD. THE
FEATURE TO THE SOUTH IS EXPECTED TO HAVE MORE WIND INFLUENCE ON
THE LAKE...BRINGING NORTHEAST FLOW FOR A PERIOD DURING THAT TIME
FRAME.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 151419
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
819 AM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* LIFR CIGS LIKELY THROUGH 16Z WITH MORE MARKED IMPROVEMENT BY MID
  DAY.

* VISIBILITY GRADUALLY IMPROVING THIS MORNING WITH FOG AND PATCHY
  DRIZZLE KEEPING THINGS IFR EARLY.

* SOUTH WINDS BECOMING SOUTHEASTERLY LATER THIS MORNING AND
  INCREASING TO 12-14KT BY EARLY AFTERNOON AND PERSISTING THROUGH
  EVENING.

* SHOWERS MOVING IN EARLY THIS AFTERNOON. SHOWER POTENTIAL PERSIST
  THROUGH REST OF TAF.

* RETURNING IFR OR LIFR CONDITIONS TONIGHT IN FOG/DRIZZLE.

RODRIGUEZ/MTF

//DISCUSSION...UPDATED 12Z...

SOUTHERLY FLOW AHEAD OF APPROACHING LOW PRESSURE CONTINUES OVER
THE AREA THIS MORNING. CIGS AND VISBYS HAVE SHOWN A SLIGHT
IMPROVING TREND AT A MAJORITY OF AREA AIRPORTS SINCE 10Z AND THAT
TREND WILL VERY GRADUALLY CONTINUE THROUGH 14Z-15Z BEFORE A
LIKELY MORE RAPID IMPROVEMENT. THE LOWEST VISBYS EARLY THIS
MORNING SEEM TO BE ASSOCIATED WITH BOTH DRIZZLE AND FOG...WITH
THE DRIZZLE NOW BEING PATCHY.

IT IS NOT IMPOSSIBLE THAT MDW STILL DROPS DOWN TO 200FT PRIOR TO
14Z...HOWEVER IT WOULD LIKELY NOW BE VERY TEMPORARY...AND SO
CONTINUE TAF ABOVE THAT.

THIS AFTERNOON THE SOUTH WINDS WILL BECOME MORE SOUTHEAST AND
INCREASE IN SPEED WITH THE APPROACHING LOW. IN ADDITION...AN ARC
OF SHOWERS THAT EXTENDS FROM SOUTHEAST IA THROUGH WESTERN IL AS OF
12Z WILL MOVE NORTHEAST OVER THE AREA. THE OVERALL COVERAGE LIKELY
WILL DISSIPATE SOME...BUT MOST AREAS SHOULD SEE SHOWERS DURING THE
EARLY TO MID AFTERNOON. WHAT THE CIGS AND VISBYS WILL DO
UNDERNEATH THESE SHOWERS IS DIFFICULT TO SAY GIVEN THE MOIST AIR
MASS AND ALREADY SOMEWHAT LOW VISBYS AND CIGS...BUT WOULD EXPECT
MAINLY MVFR/VFR.

BEHIND THE INITIAL ARC OF SHOWERS...OVERALL SUPPORT FOR SCATTERED
SHOWERS AND PATCHY DRIZZLE WILL CONTINUE. WITH THE LOW EXPECTED TO
MOVE DIRECTLY OVER THE AREA TONIGHT...CIGS AND VISBYS WILL ONCE
AGAIN COME DOWN AND THE LIKELIHOOD IS INCREASING THAT IT IS BACK
INTO THE LIFR CATEGORY. BEHIND THE LOW...WINDS WILL BECOME
NORTHWEST AND INCREASE IN SPEED INTO THE DAY TUESDAY.

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH IN CIG AND VISBY IMPROVEMENT...MEDIUM IN SPECIFIC TIMING
  AND EXTENT OF IMPROVEMENT.

* HIGH IN WINDS.

* MEDIUM-HIGH IN SHOWERS DURING THE EARLY TO MID AFTERNOON. LOW IN
  WHAT CIGS AND VISBYS WILL BE DURING RAIN.

* HIGH IN RETURNING IFR TONIGHT. LOW ON HOW FAR CONDITIONS WILL
  DROP.

RODRIGUEZ/MTF

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
212 AM CST

SOUTH TO SOUTHEAST WINDS WILL PREVAIL OVER THE LAKE TODAY AND INTO
TONIGHT. ON THESE WINDS CONTINUED HIGH MOISTURE WILL STEER OVER THE
LAKE. WET BULB TEMPERATURE VALUES WELL IN EXCESS OF THE WATER
TEMPERATURES SHOULD CONTINUE FOG. WEB CAM IMAGERY FROM THE
CHICAGO CRIB ALONG WITH A SHIP OBSERVATION WEST OF MUSKEGON EARLY
THIS MORNING INDICATE THE PRESENCE OF DENSE FOG AND DO NOT SEE
THAT IMMEDIATELY DEPARTING. SO HAVE GONE WITH AN ADVISORY FOR THE
OPEN WATER AND NEARSHORE AREAS OF ILLINOIS AND INDIANA THROUGH
TODAY. ITS POSSIBLE SCATTERED SHOWERS THIS AFTERNOON...ALONG WITH
OFFSHORE FLOW...HELPS THE FOG TO EASE SOME IN THE ILLINOIS AND
INDIANA NEARSHORES...BUT CONFIDENCE ON THIS IS LOW.

LOW PRESSURE WILL MOVE ACROSS THE SOUTHERN PART OF THE LAKE TONIGHT
BRINGING A LULL IN THE WINDS...BUT AS THE LOW MOVES EAST DURING THE
DAY TUESDAY...NORTHWEST WINDS WILL QUICKLY RAMP UP. STILL EXPECTING
AN 18 TO MAYBE 24-HOUR PERIOD OR SO OF 30 KT WINDS OVER MUCH OF THE
OPEN WATER AS MODEL GUIDANCE IS IN GOOD CONSISTENT AGREEMENT WITH
THIS. HIGH PRESSURE WILL EVENTUALLY BUILD OVER THE LAKE ON
THURSDAY BUT WEAKENING AS IT DOES. LOW PRESSURE IS EXPECTED BOTH
NORTH AND SOUTH OF THE LAKE DURING THE FRIDAY/SATURDAY PERIOD. THE
FEATURE TO THE SOUTH IS EXPECTED TO HAVE MORE WIND INFLUENCE ON
THE LAKE...BRINGING NORTHEAST FLOW FOR A PERIOD DURING THAT TIME
FRAME.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 151157
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
557 AM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* LIFR CIGS LIKELY THROUGH 14Z WITH MORE MARKED IMPROVEMENT LATE
  THIS MORNING.

* VISIBILITY GRADUALLY IMPROVING THIS MORNING WITH FOG AND PATCHY
  DRIZZLE KEEPING THINGS IFR EARLY.

* SOUTH WINDS BECOMING SOUTHEASTERLY LATER THIS MORNING AND
  INCREASING TO 12-14KT BY EARLY AFTERNOON AND PERSISTING THROUGH
  EVENING.

* SHOWERS MOVING IN EARLY THIS AFTERNOON. SHOWER POTENTIAL PERSIST
  THROUGH REST OF TAF.

* RETURNING IFR OR LIFR CONDITIONS TONIGHT IN FOG/DRIZZLE.


//DISCUSSION...UPDATED 12Z...

SOUTHERLY FLOW AHEAD OF APPROACHING LOW PRESSURE CONTINUES OVER
THE AREA THIS MORNING. CIGS AND VISBYS HAVE SHOWN A SLIGHT
IMPROVING TREND AT A MAJORITY OF AREA AIRPORTS SINCE 10Z AND THAT
TREND WILL VERY GRADUALLY CONTINUE THROUGH 14Z-15Z BEFORE A
LIKELY MORE RAPID IMPROVEMENT. THE LOWEST VISBYS EARLY THIS
MORNING SEEM TO BE ASSOCIATED WITH BOTH DRIZZLE AND FOG...WITH
THE DRIZZLE NOW BEING PATCHY.

IT IS NOT IMPOSSIBLE THAT MDW STILL DROPS DOWN TO 200FT PRIOR TO
14Z...HOWEVER IT WOULD LIKELY NOW BE VERY TEMPORARY...AND SO
CONTINUE TAF ABOVE THAT.

THIS AFTERNOON THE SOUTH WINDS WILL BECOME MORE SOUTHEAST AND
INCREASE IN SPEED WITH THE APPROACHING LOW. IN ADDITION...AN ARC
OF SHOWERS THAT EXTENDS FROM SOUTHEAST IA THROUGH WESTERN IL AS OF
12Z WILL MOVE NORTHEAST OVER THE AREA. THE OVERALL COVERAGE LIKELY
WILL DISSIPATE SOME...BUT MOST AREAS SHOULD SEE SHOWERS DURING THE
EARLY TO MID AFTERNOON. WHAT THE CIGS AND VISBYS WILL DO
UNDERNEATH THESE SHOWERS IS DIFFICULT TO SAY GIVEN THE MOIST AIR
MASS AND ALREADY SOMEWHAT LOW VISBYS AND CIGS...BUT WOULD EXPECT
MAINLY MVFR/VFR.

BEHIND THE INITIAL ARC OF SHOWERS...OVERALL SUPPORT FOR SCATTERED
SHOWERS AND PATCHY DRIZZLE WILL CONTINUE. WITH THE LOW EXPECTED TO
MOVE DIRECTLY OVER THE AREA TONIGHT...CIGS AND VISBYS WILL ONCE
AGAIN COME DOWN AND THE LIKELIHOOD IS INCREASING THAT IT IS BACK
INTO THE LIFR CATEGORY. BEHIND THE LOW...WINDS WILL BECOME
NORTHWEST AND INCREASE IN SPEED INTO THE DAY TUESDAY.


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH IN CIG AND VISBY IMPROVEMENT WITH THE LOWEST CONDITIONS
  THIS MORNING BEING BASICALLY WHAT THEY ARE AT 12Z. MEDIUM IN
  SPECIFIC TIMING.

* HIGH IN WINDS.

* MEDIUM-HIGH IN SHOWERS DURING THE EARLY TO MID AFTERNOON. LOW IN
  WHAT CIGS AND VISBYS WILL BE DURING RAIN.

* HIGH IN RETURNING IFR TONIGHT. LOW ON HOW FAR CONDITIONS WILL
  DROP.


//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
212 AM CST

SOUTH TO SOUTHEAST WINDS WILL PREVAIL OVER THE LAKE TODAY AND INTO
TONIGHT. ON THESE WINDS CONTINUED HIGH MOISTURE WILL STEER OVER THE
LAKE. WET BULB TEMPERATURE VALUES WELL IN EXCESS OF THE WATER
TEMPERATURES SHOULD CONTINUE FOG. WEB CAM IMAGERY FROM THE
CHICAGO CRIB ALONG WITH A SHIP OBSERVATION WEST OF MUSKEGON EARLY
THIS MORNING INDICATE THE PRESENCE OF DENSE FOG AND DO NOT SEE
THAT IMMEDIATELY DEPARTING. SO HAVE GONE WITH AN ADVISORY FOR THE
OPEN WATER AND NEARSHORE AREAS OF ILLINOIS AND INDIANA THROUGH
TODAY. ITS POSSIBLE SCATTERED SHOWERS THIS AFTERNOON...ALONG WITH
OFFSHORE FLOW...HELPS THE FOG TO EASE SOME IN THE ILLINOIS AND
INDIANA NEARSHORES...BUT CONFIDENCE ON THIS IS LOW.

LOW PRESSURE WILL MOVE ACROSS THE SOUTHERN PART OF THE LAKE TONIGHT
BRINGING A LULL IN THE WINDS...BUT AS THE LOW MOVES EAST DURING THE
DAY TUESDAY...NORTHWEST WINDS WILL QUICKLY RAMP UP. STILL EXPECTING
AN 18 TO MAYBE 24-HOUR PERIOD OR SO OF 30 KT WINDS OVER MUCH OF THE
OPEN WATER AS MODEL GUIDANCE IS IN GOOD CONSISTENT AGREEMENT WITH
THIS. HIGH PRESSURE WILL EVENTUALLY BUILD OVER THE LAKE ON
THURSDAY BUT WEAKENING AS IT DOES. LOW PRESSURE IS EXPECTED BOTH
NORTH AND SOUTH OF THE LAKE DURING THE FRIDAY/SATURDAY PERIOD. THE
FEATURE TO THE SOUTH IS EXPECTED TO HAVE MORE WIND INFLUENCE ON
THE LAKE...BRINGING NORTHEAST FLOW FOR A PERIOD DURING THAT TIME
FRAME.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL 8 AM MONDAY.

IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 151157
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
557 AM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* LIFR CIGS LIKELY THROUGH 14Z WITH MORE MARKED IMPROVEMENT LATE
  THIS MORNING.

* VISIBILITY GRADUALLY IMPROVING THIS MORNING WITH FOG AND PATCHY
  DRIZZLE KEEPING THINGS IFR EARLY.

* SOUTH WINDS BECOMING SOUTHEASTERLY LATER THIS MORNING AND
  INCREASING TO 12-14KT BY EARLY AFTERNOON AND PERSISTING THROUGH
  EVENING.

* SHOWERS MOVING IN EARLY THIS AFTERNOON. SHOWER POTENTIAL PERSIST
  THROUGH REST OF TAF.

* RETURNING IFR OR LIFR CONDITIONS TONIGHT IN FOG/DRIZZLE.


//DISCUSSION...UPDATED 12Z...

SOUTHERLY FLOW AHEAD OF APPROACHING LOW PRESSURE CONTINUES OVER
THE AREA THIS MORNING. CIGS AND VISBYS HAVE SHOWN A SLIGHT
IMPROVING TREND AT A MAJORITY OF AREA AIRPORTS SINCE 10Z AND THAT
TREND WILL VERY GRADUALLY CONTINUE THROUGH 14Z-15Z BEFORE A
LIKELY MORE RAPID IMPROVEMENT. THE LOWEST VISBYS EARLY THIS
MORNING SEEM TO BE ASSOCIATED WITH BOTH DRIZZLE AND FOG...WITH
THE DRIZZLE NOW BEING PATCHY.

IT IS NOT IMPOSSIBLE THAT MDW STILL DROPS DOWN TO 200FT PRIOR TO
14Z...HOWEVER IT WOULD LIKELY NOW BE VERY TEMPORARY...AND SO
CONTINUE TAF ABOVE THAT.

THIS AFTERNOON THE SOUTH WINDS WILL BECOME MORE SOUTHEAST AND
INCREASE IN SPEED WITH THE APPROACHING LOW. IN ADDITION...AN ARC
OF SHOWERS THAT EXTENDS FROM SOUTHEAST IA THROUGH WESTERN IL AS OF
12Z WILL MOVE NORTHEAST OVER THE AREA. THE OVERALL COVERAGE LIKELY
WILL DISSIPATE SOME...BUT MOST AREAS SHOULD SEE SHOWERS DURING THE
EARLY TO MID AFTERNOON. WHAT THE CIGS AND VISBYS WILL DO
UNDERNEATH THESE SHOWERS IS DIFFICULT TO SAY GIVEN THE MOIST AIR
MASS AND ALREADY SOMEWHAT LOW VISBYS AND CIGS...BUT WOULD EXPECT
MAINLY MVFR/VFR.

BEHIND THE INITIAL ARC OF SHOWERS...OVERALL SUPPORT FOR SCATTERED
SHOWERS AND PATCHY DRIZZLE WILL CONTINUE. WITH THE LOW EXPECTED TO
MOVE DIRECTLY OVER THE AREA TONIGHT...CIGS AND VISBYS WILL ONCE
AGAIN COME DOWN AND THE LIKELIHOOD IS INCREASING THAT IT IS BACK
INTO THE LIFR CATEGORY. BEHIND THE LOW...WINDS WILL BECOME
NORTHWEST AND INCREASE IN SPEED INTO THE DAY TUESDAY.


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH IN CIG AND VISBY IMPROVEMENT WITH THE LOWEST CONDITIONS
  THIS MORNING BEING BASICALLY WHAT THEY ARE AT 12Z. MEDIUM IN
  SPECIFIC TIMING.

* HIGH IN WINDS.

* MEDIUM-HIGH IN SHOWERS DURING THE EARLY TO MID AFTERNOON. LOW IN
  WHAT CIGS AND VISBYS WILL BE DURING RAIN.

* HIGH IN RETURNING IFR TONIGHT. LOW ON HOW FAR CONDITIONS WILL
  DROP.


//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...MVFR POSSIBLE. NORTHWEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY...MVFR POSSIBLE. SLGT CHANCE OF SNOW DURING THE NIGHT.
         NORTHEAST WINDS.
SATURDAY...MVFR POSSIBLE. NORTH WINDS.
SUNDAY...VFR LIKELY. NORTHWEST WINDS.

MTF

&&

.MARINE...
212 AM CST

SOUTH TO SOUTHEAST WINDS WILL PREVAIL OVER THE LAKE TODAY AND INTO
TONIGHT. ON THESE WINDS CONTINUED HIGH MOISTURE WILL STEER OVER THE
LAKE. WET BULB TEMPERATURE VALUES WELL IN EXCESS OF THE WATER
TEMPERATURES SHOULD CONTINUE FOG. WEB CAM IMAGERY FROM THE
CHICAGO CRIB ALONG WITH A SHIP OBSERVATION WEST OF MUSKEGON EARLY
THIS MORNING INDICATE THE PRESENCE OF DENSE FOG AND DO NOT SEE
THAT IMMEDIATELY DEPARTING. SO HAVE GONE WITH AN ADVISORY FOR THE
OPEN WATER AND NEARSHORE AREAS OF ILLINOIS AND INDIANA THROUGH
TODAY. ITS POSSIBLE SCATTERED SHOWERS THIS AFTERNOON...ALONG WITH
OFFSHORE FLOW...HELPS THE FOG TO EASE SOME IN THE ILLINOIS AND
INDIANA NEARSHORES...BUT CONFIDENCE ON THIS IS LOW.

LOW PRESSURE WILL MOVE ACROSS THE SOUTHERN PART OF THE LAKE TONIGHT
BRINGING A LULL IN THE WINDS...BUT AS THE LOW MOVES EAST DURING THE
DAY TUESDAY...NORTHWEST WINDS WILL QUICKLY RAMP UP. STILL EXPECTING
AN 18 TO MAYBE 24-HOUR PERIOD OR SO OF 30 KT WINDS OVER MUCH OF THE
OPEN WATER AS MODEL GUIDANCE IS IN GOOD CONSISTENT AGREEMENT WITH
THIS. HIGH PRESSURE WILL EVENTUALLY BUILD OVER THE LAKE ON
THURSDAY BUT WEAKENING AS IT DOES. LOW PRESSURE IS EXPECTED BOTH
NORTH AND SOUTH OF THE LAKE DURING THE FRIDAY/SATURDAY PERIOD. THE
FEATURE TO THE SOUTH IS EXPECTED TO HAVE MORE WIND INFLUENCE ON
THE LAKE...BRINGING NORTHEAST FLOW FOR A PERIOD DURING THAT TIME
FRAME.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL 8 AM MONDAY.

IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 150936
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
336 AM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* LIFR CIGS LIKELY THROUGH 14Z-15Z...INCLUDING AS LOW AS 200 FT.

* SOMEWHAT VARIABLE VISIBILITY BUT POTENTIAL FOR PERIODS OF 3/4SM-
  2SM IN DRIZZLE/FOG CONTINUE THROUGH 14Z.

* SOUTH WINDS BECOMING SOUTHEASTERLY LATER THIS MORNING AND
  INCREASING TO AROUND 10-12KT AND PERSISTING THROUGH EVENING.

* RETURNING IFR AND POSSIBLE LIFR CONDITIONS MONDAY NIGHT IN
  FOG/DRIZZLE.

//DISCUSSION...UPDATED 09Z...

CIGS AND VISBYS GRADUALLY DETERIORATED AT ORD AND MDW BETWEEN 08Z
AND 09Z...HOWEVER ALMOST EVERY SINGLE OBSERVATION SITE TO THE WEST
AND SOUTH OF THEM HELD STEADY WITH CIGS. GIVEN THE AMAZING
PERSISTENCE OF THE CIG HEIGHT OBSERVATIONS ACROSS THE AREA AS A
WHOLE...AND THE FACT THAT SOUTH WINDS CONTINUE SOME MIXING IN THE
IMMEDIATE LOW-LEVELS...IT WOULD SEEM UNLIKELY THAT EITHER AIRPORT
WOULD HIT 100 FT CIGS. ALSO FEEL A TAD MORE CONFIDENT THAT MDW
MAY NOT DROP TO 200 FT...OR IF THEY DO IT WOULD BE BRIEF AND MORE
FAVORED PRIOR TO 12Z THAN 12Z-14Z.

PATCHY DRIZZLE AND MORE DENSE FOG CONTINUES ACROSS THE AREA AND
COULD RESULT IN LOWERING VISIBILITY THROUGH DAYBREAK...POSSIBLY AS
LOW AS 3/4SM.

PREV DISCUSSION...UPDATED 06Z...

SOUTHERLY FLOW HAS ESTABLISHED ITSELF OVER THE AREA AND FOR THE
TIME BEING THAT MEANS CONTINUED REPLENISHMENT OF MOISTURE...SO LOW
CLOUDS AND FOG WILL CONTINUE INTO MONDAY MORNING. AS OF
06Z...TDWR INDICATES DRIZZLE IS BECOMING MORE PATCHY AND
LIGHT AND THAT IS REFLECTED IN SLIGHTLY HIGHER VISIBILITY AT ORD
AND MDW. MOST OUTLYING SITES REMAIN VERY LOW IN BOTH CIG AND
VISIBILITY AND BELIEVE THE GENERAL WEATHER SETUP FAVORS CIGS AND
TO SOME DEGREE VISIBILITY TO COME BACK DOWN AT ORD AND MDW...BUT
HOW FAR IS UNCERTAIN. ALL IN ALL ANY SHIFTS WILL BE VERY SUBTLE IN
SUCH A REGIME. WILL MONITOR TRENDS CLOSELY AND MAKE AMENDMENTS AS
NEEDED.

CONDITIONS SHOULD IMPROVE DURING THE LATTER MORNING MONDAY AND AT
A QUICKER RATE THAN RECENT MORNINGS. AS LOW PRESSURE MOVES NEAR
KANSAS CITY BY MIDDAY...A LEADING ARC OF SHOWERS...LIKELY
WEAKENING SHOULD MOVE OVER THE AREA. BEHIND THIS ANOTHER SURGE OF
MOISTURE OCCURS THAT COULD SUPPORT ISOLATED/SCATTERED SHOWERS AS
WELL AS DRIZZLE AND LOWERING CLOUDS/CIGS. THE LOW IS EXPECTED TO
PASS OVER NORTHERN IL LATE MONDAY NIGHT INTO VERY EARLY TUESDAY
MORNING. THIS MEANS DIMINISHING WINDS. WHILE SOME SHOWERS /AND
EVEN POSSIBLY A STRAY STORM/ WILL BE AROUND MONDAY NIGHT...THE
GENERAL CONDITIONS SHOULD DROP BACK TO IFR IF NOT LIFR BY DAYBREAK
TUESDAY.

SOUTHERLY WINDS WILL INCH SOUTHEASTWARD AND INCREASE IN SPEED AS
THE LOW PRESSURE APPROACHES. WINDS SHOULD REMAIN FROM THE
SOUTHEAST MONDAY NIGHT BEFORE POSSIBLY BECOMING VARIABLE INTO
EARLY TUESDAY MORNING AS THE LOW PASSES OVERHEAD.

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH IN LIFR CIGS THROUGH AT LEAST 14Z. LOW ON SPECIFIC 200 OR
  300 FT HEIGHTS...BUT GIVEN RECENT TRENDS CONFIDENCE HAS SLIGHTLY
  INCREASED THAT IF MDW EXPERIENCES 200 FT IT MAY BE BRIEF AND
  MORE SO 12Z OR EARLIER.

* LOW-MEDIUM IN SPECIFIC TIMING OF WHEN CIGS LIFT THIS MORNING.

* LOW-MEDIUM IN VISIBILITY THROUGH MUCH OF THE TAF WITH SOME
  VARIABILITY LIKELY THROUGH DAYBREAK...WITH POSSIBLY AS LOW AS
  3/4SM IN DRIZZLE/FOG.

* HIGH IN WIND TRENDS THROUGH 00Z TUESDAY. MEDIUM AFTER.

* MEDIUM IN CONDITIONS DETERIORATING AGAIN MONDAY NIGHT.

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...MVFR LIKELY...IFR POSSIBLE. CHANCE OF RAIN...POSSIBLY
MIXING WITH WET SNOW BEFORE ENDING.

WEDNESDAY...MVFR CIGS POSSIBLE...ESPECIALLY EARLY.

THURSDAY THROUGH SATURDAY...PRIMARILY VFR.

MTF/IZZI

&&

.MARINE...
212 AM CST

SOUTH TO SOUTHEAST WINDS WILL PREVAIL OVER THE LAKE TODAY AND INTO
TONIGHT. ON THESE WINDS CONTINUED HIGH MOISTURE WILL STEER OVER THE
LAKE. WET BULB TEMPERATURE VALUES WELL IN EXCESS OF THE WATER
TEMPERATURES SHOULD CONTINUE FOG. WEB CAM IMAGERY FROM THE
CHICAGO CRIB ALONG WITH A SHIP OBSERVATION WEST OF MUSKEGON EARLY
THIS MORNING INDICATE THE PRESENCE OF DENSE FOG AND DO NOT SEE
THAT IMMEDIATELY DEPARTING. SO HAVE GONE WITH AN ADVISORY FOR THE
OPEN WATER AND NEARSHORE AREAS OF ILLINOIS AND INDIANA THROUGH
TODAY. ITS POSSIBLE SCATTERED SHOWERS THIS AFTERNOON...ALONG WITH
OFFSHORE FLOW...HELPS THE FOG TO EASE SOME IN THE ILLINOIS AND
INDIANA NEARSHORES...BUT CONFIDENCE ON THIS IS LOW.

LOW PRESSURE WILL MOVE ACROSS THE SOUTHERN PART OF THE LAKE TONIGHT
BRINGING A LULL IN THE WINDS...BUT AS THE LOW MOVES EAST DURING THE
DAY TUESDAY...NORTHWEST WINDS WILL QUICKLY RAMP UP. STILL EXPECTING
AN 18 TO MAYBE 24-HOUR PERIOD OR SO OF 30 KT WINDS OVER MUCH OF THE
OPEN WATER AS MODEL GUIDANCE IS IN GOOD CONSISTENT AGREEMENT WITH
THIS. HIGH PRESSURE WILL EVENTUALLY BUILD OVER THE LAKE ON
THURSDAY BUT WEAKENING AS IT DOES. LOW PRESSURE IS EXPECTED BOTH
NORTH AND SOUTH OF THE LAKE DURING THE FRIDAY/SATURDAY PERIOD. THE
FEATURE TO THE SOUTH IS EXPECTED TO HAVE MORE WIND INFLUENCE ON
THE LAKE...BRINGING NORTHEAST FLOW FOR A PERIOD DURING THAT TIME
FRAME.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL 8 AM MONDAY.

IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
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000
FXUS63 KLOT 150936
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
336 AM CST MON DEC 15 2014

.SHORT TERM...

TODAY THROUGH TUESDAY...

336 AM...FORECAST CONCERNS INCLUDE FOG THIS MORNING AND AGAIN
TONIGHT INTO TUESDAY MORNING...PRECIP TIMING/COVERAGE TODAY...
RAIN TONIGHT INTO TUESDAY AND HIGH TEMPS TODAY.

VISIBILITIES REMAIN GENERALLY ABOVE A QUARTER MILE EARLY THIS
MORNING AND HAVE SLOWLY BEEN TRENDING UP ACROSS WESTERN IL AS
TEMPERATURES HAVE CREPT INTO THE LOWER 50S. EXPECT THIS TREND TO
CONTINUE ACROSS THE WESTERN CWA OVER THE NEXT SEVERAL HOURS...BUT
CONFIDENCE IS STILL LOW AND WILL LET THE DENSE FOG ADVISORY RIDE
FOR NOW...BUT ITS POSSIBLE THAT IT COULD BE CANCELED EARLY.

A LARGE AREA OF RAIN EXTENDS FROM SOUTHERN IOWA INTO ARKANSAS AND
THIS WILL SLOWLY SPREAD NORTH/NORTHEAST THIS MORNING...AS IT
SLOWLY DISSIPATES AS INDICATED BY BOTH THE HRRR/RAP. IN ADDITION
THE TIMING HAS SLOWED WITH THIS ACTIVITY PERHAPS NOT REACHING THE
WESTERN CWA UNTIL MID MORNING AND THEN ACROSS THE REST OF THE CWA
EARLY/MID AFTERNOON. TRENDS WITH HOURLY GRIDS WILL NEED TO BE
MONITORED LATER THIS MORNING FOR TIMING/LOCATION TWEAKS AS THE
PRECIP APPROACHES.

WHILE HIGH TEMPS STRUGGLED TO REACH THE LOWER 50S IN JUST SOME
LOCATIONS ON SUNDAY...THERE IS A LARGER AREA OF LOWER 50S ACROSS
MUCH OF SOUTHERN IA...MO AND WESTERN IL AHEAD OF THE SURFACE LOW
THAT WILL LIKELY ADVECT ACROSS MUCH OF THE CWA TODAY. THUS LOWER
50S STILL SEEM REASONABLE FOR MOST AREAS. TEMPS WILL SLOWLY FALL
BACK THROUGH THE UPPER/MID 40S OVERNIGHT. AS THE LOW MOVES ACROSS
THE REGION LATER THIS EVENING AND OVERNIGHT...EXPECT PERIODS OF
LIGHT RAIN THROUGH MUCH OF THE NIGHT AND INTO TUESDAY MORNING...
THOUGH QPF AMOUNTS WILL GENERALLY BE LIGHT...IN THE 0.2 TO 0.3
INCH RANGE. WITH LIGHT WINDS AS THE LOW MOVES THROUGH...SOME
POTENTIAL FOR FOG BUT LOW CONFIDENCE REGARDING VISIBILITIES
GIVEN THE EXPECTED RAIN THOUGH WIDESPREAD DENSE FOG IS UNLIKELY.

THE LOW CONTINUES ACROSS SOUTHERN LOWER MICHIGAN TUESDAY MORNING
WITH WINDS SHIFTING TO THE NORTHWEST AND BECOMING GUSTY BY LATE
MORNING INTO THE AFTERNOON. THE COLDER AIR APPEARS TO OOZE INTO
THE CWA RATHER THAN QUICKLY SWEEP ACROSS THE AREA. SO WHILE TEMPS
WILL STILL SLOWLY FALL...MUCH OF THE MORNING WILL LIKELY BE
THROUGH THE LOWER 40S INTO THE UPPER 30S...WITH TEMPS THEN
CONTINUING INTO THE LOWER/MID 30S IN THE AFTERNOON. MAINTAINED A
SIMILAR TRANSITION TO A RAIN/SNOW MIX LATE MORNING/EARLY AFTERNOON
FROM WEST TO EAST...BUT PRECIP WILL BE ENDING AS THE COLUMN IS
COOLING ENOUGH FOR SNOW...SO NOT EXPECTING ANY ACCUMULATION. CMS

&&

.LONG TERM...

TUESDAY NIGHT THROUGH SUNDAY...

336 AM...COLDER FOR THE EXTENDED WITH A SLIGHT CHANCE OF SNOW
THIS WEEKEND.

A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TUESDAY INTO WEDNESDAY...AND REMAIN NEARLY STATIONARY FROM THE
NORTHERN PLAINS/WESTERN LAKES INTO THE OHIO VALLEY INTO THURSDAY
NIGHT. THIS SHOULD ALLOW FOR SOME BREAKS IN THE CLOUDS WHICH WILL
ALLOW TEMPS TO DROP OFF INTO THE 20S AT NIGHT...POSSIBLY SOME
TEENS IN THE FAVORED COLDER AREAS WITH HIGHS ONLY IN THE UPPER 20S
TO LOWER 30S. PRECIP WILL BE SUPPRESSED TO THE SOUTH OF THE AREA
THROUGH FRIDAY. THE GFS CONTINUES TO BRING A SWATH OF LIGHT PRECIP
ACROSS THE REGION FRIDAY NIGHT INTO EARLY SATURDAY AND NOW THE
ECMWF HAS TRENDED A BIT FURTHER NORTH...BUT NOT UNTIL SATURDAY AND
SATURDAY NIGHT AND MAINTAINED LOW CHANCE POPS DURING THIS TIME.
CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* LIFR CIGS LIKELY THROUGH 14Z-15Z...INCLUDING AS LOW AS 200 FT.

* SOMEWHAT VARIABLE VISIBILITY BUT POTENTIAL FOR PERIODS OF 3/4SM-
  2SM IN DRIZZLE/FOG CONTINUE THROUGH 14Z.

* SOUTH WINDS BECOMING SOUTHEASTERLY LATER THIS MORNING AND
  INCREASING TO AROUND 10-12KT AND PERSISTING THROUGH EVENING.

* RETURNING IFR AND POSSIBLE LIFR CONDITIONS MONDAY NIGHT IN
  FOG/DRIZZLE.

//DISCUSSION...UPDATED 09Z...

CIGS AND VISBYS GRADUALLY DETERIORATED AT ORD AND MDW BETWEEN 08Z
AND 09Z...HOWEVER ALMOST EVERY SINGLE OBSERVATION SITE TO THE WEST
AND SOUTH OF THEM HELD STEADY WITH CIGS. GIVEN THE AMAZING
PERSISTENCE OF THE CIG HEIGHT OBSERVATIONS ACROSS THE AREA AS A
WHOLE...AND THE FACT THAT SOUTH WINDS CONTINUE SOME MIXING IN THE
IMMEDIATE LOW-LEVELS...IT WOULD SEEM UNLIKELY THAT EITHER AIRPORT
WOULD HIT 100 FT CIGS. ALSO FEEL A TAD MORE CONFIDENT THAT MDW
MAY NOT DROP TO 200 FT...OR IF THEY DO IT WOULD BE BRIEF AND MORE
FAVORED PRIOR TO 12Z THAN 12Z-14Z.

PATCHY DRIZZLE AND MORE DENSE FOG CONTINUES ACROSS THE AREA AND
COULD RESULT IN LOWERING VISIBILITY THROUGH DAYBREAK...POSSIBLY AS
LOW AS 3/4SM.

PREV DISCUSSION...UPDATED 06Z...

SOUTHERLY FLOW HAS ESTABLISHED ITSELF OVER THE AREA AND FOR THE
TIME BEING THAT MEANS CONTINUED REPLENISHMENT OF MOISTURE...SO LOW
CLOUDS AND FOG WILL CONTINUE INTO MONDAY MORNING. AS OF
06Z...TDWR INDICATES DRIZZLE IS BECOMING MORE PATCHY AND
LIGHT AND THAT IS REFLECTED IN SLIGHTLY HIGHER VISIBILITY AT ORD
AND MDW. MOST OUTLYING SITES REMAIN VERY LOW IN BOTH CIG AND
VISIBILITY AND BELIEVE THE GENERAL WEATHER SETUP FAVORS CIGS AND
TO SOME DEGREE VISIBILITY TO COME BACK DOWN AT ORD AND MDW...BUT
HOW FAR IS UNCERTAIN. ALL IN ALL ANY SHIFTS WILL BE VERY SUBTLE IN
SUCH A REGIME. WILL MONITOR TRENDS CLOSELY AND MAKE AMENDMENTS AS
NEEDED.

CONDITIONS SHOULD IMPROVE DURING THE LATTER MORNING MONDAY AND AT
A QUICKER RATE THAN RECENT MORNINGS. AS LOW PRESSURE MOVES NEAR
KANSAS CITY BY MIDDAY...A LEADING ARC OF SHOWERS...LIKELY
WEAKENING SHOULD MOVE OVER THE AREA. BEHIND THIS ANOTHER SURGE OF
MOISTURE OCCURS THAT COULD SUPPORT ISOLATED/SCATTERED SHOWERS AS
WELL AS DRIZZLE AND LOWERING CLOUDS/CIGS. THE LOW IS EXPECTED TO
PASS OVER NORTHERN IL LATE MONDAY NIGHT INTO VERY EARLY TUESDAY
MORNING. THIS MEANS DIMINISHING WINDS. WHILE SOME SHOWERS /AND
EVEN POSSIBLY A STRAY STORM/ WILL BE AROUND MONDAY NIGHT...THE
GENERAL CONDITIONS SHOULD DROP BACK TO IFR IF NOT LIFR BY DAYBREAK
TUESDAY.

SOUTHERLY WINDS WILL INCH SOUTHEASTWARD AND INCREASE IN SPEED AS
THE LOW PRESSURE APPROACHES. WINDS SHOULD REMAIN FROM THE
SOUTHEAST MONDAY NIGHT BEFORE POSSIBLY BECOMING VARIABLE INTO
EARLY TUESDAY MORNING AS THE LOW PASSES OVERHEAD.

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH IN LIFR CIGS THROUGH AT LEAST 14Z. LOW ON SPECIFIC 200 OR
  300 FT HEIGHTS...BUT GIVEN RECENT TRENDS CONFIDENCE HAS SLIGHTLY
  INCREASED THAT IF MDW EXPERIENCES 200 FT IT MAY BE BRIEF AND
  MORE SO 12Z OR EARLIER.

* LOW-MEDIUM IN SPECIFIC TIMING OF WHEN CIGS LIFT THIS MORNING.

* LOW-MEDIUM IN VISIBILITY THROUGH MUCH OF THE TAF WITH SOME
  VARIABILITY LIKELY THROUGH DAYBREAK...WITH POSSIBLY AS LOW AS
  3/4SM IN DRIZZLE/FOG.

* HIGH IN WIND TRENDS THROUGH 00Z TUESDAY. MEDIUM AFTER.

* MEDIUM IN CONDITIONS DETERIORATING AGAIN MONDAY NIGHT.

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...MVFR LIKELY...IFR POSSIBLE. CHANCE OF RAIN...POSSIBLY
MIXING WITH WET SNOW BEFORE ENDING.

WEDNESDAY...MVFR CIGS POSSIBLE...ESPECIALLY EARLY.

THURSDAY THROUGH SATURDAY...PRIMARILY VFR.

MTF/IZZI

&&

.MARINE...
212 AM CST

SOUTH TO SOUTHEAST WINDS WILL PREVAIL OVER THE LAKE TODAY AND INTO
TONIGHT. ON THESE WINDS CONTINUED HIGH MOISTURE WILL STEER OVER THE
LAKE. WET BULB TEMPERATURE VALUES WELL IN EXCESS OF THE WATER
TEMPERATURES SHOULD CONTINUE FOG. WEB CAM IMAGERY FROM THE
CHICAGO CRIB ALONG WITH A SHIP OBSERVATION WEST OF MUSKEGON EARLY
THIS MORNING INDICATE THE PRESENCE OF DENSE FOG AND DO NOT SEE
THAT IMMEDIATELY DEPARTING. SO HAVE GONE WITH AN ADVISORY FOR THE
OPEN WATER AND NEARSHORE AREAS OF ILLINOIS AND INDIANA THROUGH
TODAY. ITS POSSIBLE SCATTERED SHOWERS THIS AFTERNOON...ALONG WITH
OFFSHORE FLOW...HELPS THE FOG TO EASE SOME IN THE ILLINOIS AND
INDIANA NEARSHORES...BUT CONFIDENCE ON THIS IS LOW.

LOW PRESSURE WILL MOVE ACROSS THE SOUTHERN PART OF THE LAKE TONIGHT
BRINGING A LULL IN THE WINDS...BUT AS THE LOW MOVES EAST DURING THE
DAY TUESDAY...NORTHWEST WINDS WILL QUICKLY RAMP UP. STILL EXPECTING
AN 18 TO MAYBE 24-HOUR PERIOD OR SO OF 30 KT WINDS OVER MUCH OF THE
OPEN WATER AS MODEL GUIDANCE IS IN GOOD CONSISTENT AGREEMENT WITH
THIS. HIGH PRESSURE WILL EVENTUALLY BUILD OVER THE LAKE ON
THURSDAY BUT WEAKENING AS IT DOES. LOW PRESSURE IS EXPECTED BOTH
NORTH AND SOUTH OF THE LAKE DURING THE FRIDAY/SATURDAY PERIOD. THE
FEATURE TO THE SOUTH IS EXPECTED TO HAVE MORE WIND INFLUENCE ON
THE LAKE...BRINGING NORTHEAST FLOW FOR A PERIOD DURING THAT TIME
FRAME.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL 8 AM MONDAY.

IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 6 PM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






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