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000
FXUS63 KLOT 110408
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1008 PM CST WED FEB 10 2016

.UPDATE...
901 PM CST

SKIES HAVE BEEN SLUGGISH TO THIN THIS EVENING...HOWEVER THE LAST
FEW HOURS IR IMAGERY INDICATES A STEADY EROSION TO THE CLOUDS
ACROSS NORTHERN IL STRETCHING NORTH INTO SOUTHERN WISC. FURTHER
UPSTREAM THERE IS A WEAK MID-LVL VORT THAT WAS SPREADING SOME
CLOUDS ACROSS WESTCENTRAL WISC/NORTHEAST IA...BUT IS EXPECTED TO
CLIP THE WESTERN FORECAST AREA OVERNIGHT...AND EXIT TO THE SOUTH
OF THE FORECAST AREA PRIOR TO DAYBREAK.

HIGH PRESSURE AXIS WLL REMAIN POSITIONED TO THE NORTHWEST OF THE
REGION...HOWEVER WILL SLOWLY SAG SOUTH BY DAYBREAK THUR AND
CONTINUE TO BE PROGRESSIVE AND SLIDE SOUTHEAST OF THE AREA BY FRI
AFTN/EVE. TEMPS OVERNIGHT TONIGHT WILL HOVER AROUND ZERO TO THE
SINGLE DIGITS ABOVE ZERO WEST OF LAKE MICHIGAN...WHILE AREAS
ADJACENT TO THE LAKE WILL LIKELY REMAIN AROUND 5 TO 10 DEGREES
ABOVE ZERO. WHILE WINDS HAVE DIMINISHED A LITTLE THIS
EVENING...WIND CHILL VALUES WILL CONTINUE TO RANGE FROM AROUND
ZERO TO THE SINGLE DIGITS BELOW ZERO. ALONG AND NORTH OF A
LASALLE TO WAUKEGAN LINE WIND CHILL VALUES MAY DIP FURTHER TO -10
TO -15 PRIOR TO DAYBREAK.

BEACHLER

&&

.SHORT TERM...

TONIGHT AND THURSDAY...

248 PM...ONLY CONCERN IS LIGHT LAKE EFFECT SNOW SHOWERS IN FAR
NORTHEAST PORTER COUNTY.

A RIDGE AXIS EXTENDS FROM MN SOUTHEAST TO CENTRAL IL THIS
AFTERNOON AND WILL SLOWLY TURN EASTERLY AS IT BUILDS ACROSS THE
OHIO VALLEY THURSDAY. CURRENT WAVE WITH LIGHT SNOW OVER PARTS OF
IA INTO SOUTHWEST IL WILL REMAIN SOUTHWEST OF THE CWA. WEST/
NORTHWEST WINDS WILL MAINTAIN THE CHANCE OF LAKE EFFECT SNOW
SHOWERS OVER FAR NORTHEAST PORTER COUNTY TONIGHT WITH MINOR NEW
ACCUMULATIONS POSSIBLE. THESE WILL BEGIN TO DIMINISH THURSDAY AS
WINDS TURN MORE WESTERLY. LOW TEMPS TONIGHT WILL DIP INTO THE LOW
SINGLE DIGITS WITH THE USUAL COLD SPOTS POSSIBLY DIPPING BELOW
ZERO. THESE TEMPS WILL COMBINE WITH NORTHWEST WINDS TO ALLOW WIND
CHILL VALUES 10 BELOW ZERO. CMS

&&

.LONG TERM...

THURSDAY NIGHT THROUGH WEDNESDAY...

248 PM...FORECAST CONCERNS INCLUDE LIGHT SNOW FRIDAY MORNING...
WIND CHILLS POSSIBLY REACHING ADVISORY CRITERIA SATURDAY MORNING
AND ANOTHER PERIOD OF LIGHT SNOW SUNDAY AFTERNOON/SUNDAY NIGHT.

ANOTHER SURGE OF VERY COLD AIR WILL ARRIVE FRIDAY AFTERNOON INTO
FRIDAY NIGHT AND AHEAD OF THIS SURGE...THERE WILL BE A PERIOD OF
LIGHT SNOW FRIDAY MORNING. THERE IS SOME DIFFERENCES REGARDING HOW
FAR NORTH THIS LIGHT SNOW WILL OCCUR...WITH THE GFS FURTHEST NORTH
AND ACROSS THE ENTIRE AREA. BEST CHANCES FOR LIGHT SNOW ALONG WITH
ANY MINOR ACCUMULATIONS APPEAR TO REMAIN ACROSS THE SOUTHERN CWA
AND MAINTAINED LOW CHANCE POPS FOR NOW. BUT AS TRENDS EMERGE...
HIGHER POPS MAY BE NEEDED DESPITE THE LOW QPF EXPECTED. TEMPS ALSO
APPEAR TO HOLD FAIRLY STEADY THURSDAY NIGHT INTO FRIDAY OR PERHAPS
AN EVENING LOW THEN STEADY OR SLOWLY RISING INTO FRIDAY MORNING.

AS THE COLDER AIR ARRIVES FRIDAY AFTERNOON...TEMPS WILL BEGIN TO
FALL WITH LOWS LIKELY BELOW ZERO ACROSS MUCH OF NORTHWEST IL BY
SATURDAY MORNING AND ONLY LOW SINGLE DIGITS ELSEWHERE. NORTHWEST
WINDS WILL ALSO BECOME STRONG/GUSTY FRIDAY AFTERNOON/EVENING WITH
GUSTS PERHAPS INTO THE 30 MPH RANGE. WIND CHILLS WILL LIKELY FALL
BELOW ZERO BY EARLY FRIDAY EVENING AND INTO THE 15 BELOW TO 25
BELOW ZERO RANGE SATURDAY MORNING.

WHILE THE COLDEST AIR WILL BEGIN TO PUSH EAST OF THE AREA SATURDAY
HIGHS WILL LIKELY STRUGGLE TO REACH THE MID TEENS AND THEN A SHARP
DROP SATURDAY EVENING IS POSSIBLE BUT DEPENDENT ON HOW FAST CLOUD
COVER ARRIVES WHICH MAY THEN KEEP TEMPS STEADY OR EVEN BEGIN TO
SLOWLY RISE EARLY SUNDAY MORNING. REGARDLESS...TEMPS DURING THIS
TIME PERIOD WILL LIKELY BE IN THE SINGLE DIGITS ALONG WITH WIND
CHILLS BELOW ZERO.

A CLIPPER LIKE SYSTEM WILL QUICKLY MOVE INTO THE AREA SUNDAY
AFTERNOON INTO SUNDAY NIGHT. THIS SYSTEM HAS BEEN FAIRLY
CONSISTENT FOR SEVERAL DAYS...BUT NOW APPEARS TO BE IN A WEAKENING
PHASE AS IT ARRIVES. SO WHILE IT WILL BE COLD ENOUGH THAT PRECIP
SHOULD BE ALL SNOW...FAIRLY LOW CONFIDENCE ON QPF AMOUNTS
ESPECIALLY ACROSS THE EASTERN CWA. CURRENT TRENDS WOULD SUGGEST A
FEW INCHES OF ACCUMULATION WOULD BE POSSIBLE...BUT TOO EARLY FOR
ANY SPECIFICS. TEMPS LOOK TO RISE BACK INTO THE LOW/MID 20S SUNDAY
AND THEN MAY REMAIN GENERALLY STEADY SUNDAY NIGHT INTO MONDAY
MORNING.

MONDAY AND TUESDAY APPEAR GENERALLY DRY WITH A PERIOD OF RAIN OR
SNOW POSSIBLE LATE TUESDAY NIGHT/WEDNESDAY AS WARMER AIR SPREADS
BACK INTO THE REGION THOUGH DIFFERENCES REMAIN BETWEEN THE
ECMWF/GFS. CMS

&&

.AVIATION...
FOR THE 06Z TAFS...

NO SIG CHANGES TO THE GOING FORECAST. FAIRLY QUIET FOR THE AREA
TERMINALS THROUGH TOMORROW NIGHT. CLOUD COVER WILL MAINLY BE SCT-
BKN CI ASSOCIATED WITH A STRONG UPPER JET DIVING THROUGH THE
MIDDLE MISSISSIPPI VALLEY. SFC HIGH PRESSURE EXTENDS FROM CNTRL
CANADA TO THE CENTRAL GULF COAST. THE CENTER OF THE HIGH WILL
SLIDE SOUTH OVERNIGHT AND TOMORROW...GENERALLY ALONG THE
MISSISSIPPI RIVER. THIS SHOULD KEEP WINDS GENERALLY NWLY...THOUGH
DECREASING OVERNIGHT AND TOMORROW TO ARND 5KT AS THE PRESSURE
GRADIENT WEAKENS ACROSS THE AREA. AS THE HIGH CONTINUES TO SLIDE
SOUTHEAST INTO THE OHIO VALLEY TOMORROW EVENING...WINDS SHOULD
BACK TO SWLY WHILE REMAINING ARND 5KT.

KREIN

&&

.MARINE...
202 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT WILL PERSIST
OVER LAKE MICHIGAN THROUGH TONIGHT AHEAD OF A RIDGE THAT STRETCHES
FROM THE NORTHWEST TERRITORIES INTO THE MISSISSIPPI VALLEY.
WINDS OF 30 KT AND FREEZING SPRAY WILL CONTINUE INTO SOME OF THE
OVERNIGHT HOURS THEN SHOULD DIMINISH EARLY THURSDAY AS THE HIGH
INCHES EAST ALLOWING THE GRADIENT TO RELAX. WINDS ALSO BACK TO THE
WEST ON THURSDAY AS THE HIGH BUILDS SOUTH OF LAKE MICHIGAN...THEN
FRESHEN UP AS LOW PRESSURE FORMS OVER ONTARIO. THIS LOW WILL BRING
A REINFORCING SHOT OF COLD AIR SOUTH ON FRIDAY BEHIND A TRAILING
COLD FRONT AND AS A STRONG ARCTIC HIGH BUILDS ACROSS CANADA INTO
THE UPPER MIDWEST. AT LEAST A SHORT WINDOW OF NORTHERLY GALES ARE
EXPECTED BEHIND THE COLD FRONT FRIDAY EVENING OR OVERNIGHT...THEN
WINDS SHOULD GRADUALLY DIMINISH OVER THE WEEKEND AS THE HIGH
BUILDS ACROSS THE GREAT LAKES.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 110310
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
910 PM CST WED FEB 10 2016

.UPDATE...
901 PM CST

SKIES HAVE BEEN SLUGGISH TO THIN THIS EVENING...HOWEVER THE LAST
FEW HOURS IR IMAGERY INDICATES A STEADY EROSION TO THE CLOUDS
ACROSS NORTHERN IL STRETCHING NORTH INTO SOUTHERN WISC. FURTHER
UPSTREAM THERE IS A WEAK MID-LVL VORT THAT WAS SPREADING SOME
CLOUDS ACROSS WESTCENTRAL WISC/NORTHEAST IA...BUT IS EXPECTED TO
CLIP THE WESTERN FORECAST AREA OVERNIGHT...AND EXIT TO THE SOUTH
OF THE FORECAST AREA PRIOR TO DAYBREAK.

HIGH PRESSURE AXIS WLL REMAIN POSITIONED TO THE NORTHWEST OF THE
REGION...HOWEVER WILL SLOWLY SAG SOUTH BY DAYBREAK THUR AND
CONTINUE TO BE PROGRESSIVE AND SLIDE SOUTHEAST OF THE AREA BY FRI
AFTN/EVE. TEMPS OVERNIGHT TONIGHT WILL HOVER AROUND ZERO TO THE
SINGLE DIGITS ABOVE ZERO WEST OF LAKE MICHIGAN...WHILE AREAS
ADJACENT TO THE LAKE WILL LIKELY REMAIN AROUND 5 TO 10 DEGREES
ABOVE ZERO. WHILE WINDS HAVE DIMINISHED A LITTLE THIS
EVENING...WIND CHILL VALUES WILL CONTINUE TO RANGE FROM AROUND
ZERO TO THE SINGLE DIGITS BELOW ZERO. ALONG AND NORTH OF A
LASALLE TO WAUKEGAN LINE WIND CHILL VALUES MAY DIP FURTHER TO -10
TO -15 PRIOR TO DAYBREAK.

BEACHLER

&&

.SHORT TERM...

TONIGHT AND THURSDAY...

248 PM...ONLY CONCERN IS LIGHT LAKE EFFECT SNOW SHOWERS IN FAR
NORTHEAST PORTER COUNTY.

A RIDGE AXIS EXTENDS FROM MN SOUTHEAST TO CENTRAL IL THIS
AFTERNOON AND WILL SLOWLY TURN EASTERLY AS IT BUILDS ACROSS THE
OHIO VALLEY THURSDAY. CURRENT WAVE WITH LIGHT SNOW OVER PARTS OF
IA INTO SOUTHWEST IL WILL REMAIN SOUTHWEST OF THE CWA. WEST/
NORTHWEST WINDS WILL MAINTAIN THE CHANCE OF LAKE EFFECT SNOW
SHOWERS OVER FAR NORTHEAST PORTER COUNTY TONIGHT WITH MINOR NEW
ACCUMULATIONS POSSIBLE. THESE WILL BEGIN TO DIMINISH THURSDAY AS
WINDS TURN MORE WESTERLY. LOW TEMPS TONIGHT WILL DIP INTO THE LOW
SINGLE DIGITS WITH THE USUAL COLD SPOTS POSSIBLY DIPPING BELOW
ZERO. THESE TEMPS WILL COMBINE WITH NORTHWEST WINDS TO ALLOW WIND
CHILL VALUES 10 BELOW ZERO. CMS

&&

.LONG TERM...

THURSDAY NIGHT THROUGH WEDNESDAY...

248 PM...FORECAST CONCERNS INCLUDE LIGHT SNOW FRIDAY MORNING...
WIND CHILLS POSSIBLY REACHING ADVISORY CRITERIA SATURDAY MORNING
AND ANOTHER PERIOD OF LIGHT SNOW SUNDAY AFTERNOON/SUNDAY NIGHT.

ANOTHER SURGE OF VERY COLD AIR WILL ARRIVE FRIDAY AFTERNOON INTO
FRIDAY NIGHT AND AHEAD OF THIS SURGE...THERE WILL BE A PERIOD OF
LIGHT SNOW FRIDAY MORNING. THERE IS SOME DIFFERENCES REGARDING HOW
FAR NORTH THIS LIGHT SNOW WILL OCCUR...WITH THE GFS FURTHEST NORTH
AND ACROSS THE ENTIRE AREA. BEST CHANCES FOR LIGHT SNOW ALONG WITH
ANY MINOR ACCUMULATIONS APPEAR TO REMAIN ACROSS THE SOUTHERN CWA
AND MAINTAINED LOW CHANCE POPS FOR NOW. BUT AS TRENDS EMERGE...
HIGHER POPS MAY BE NEEDED DESPITE THE LOW QPF EXPECTED. TEMPS ALSO
APPEAR TO HOLD FAIRLY STEADY THURSDAY NIGHT INTO FRIDAY OR PERHAPS
AN EVENING LOW THEN STEADY OR SLOWLY RISING INTO FRIDAY MORNING.

AS THE COLDER AIR ARRIVES FRIDAY AFTERNOON...TEMPS WILL BEGIN TO
FALL WITH LOWS LIKELY BELOW ZERO ACROSS MUCH OF NORTHWEST IL BY
SATURDAY MORNING AND ONLY LOW SINGLE DIGITS ELSEWHERE. NORTHWEST
WINDS WILL ALSO BECOME STRONG/GUSTY FRIDAY AFTERNOON/EVENING WITH
GUSTS PERHAPS INTO THE 30 MPH RANGE. WIND CHILLS WILL LIKELY FALL
BELOW ZERO BY EARLY FRIDAY EVENING AND INTO THE 15 BELOW TO 25
BELOW ZERO RANGE SATURDAY MORNING.

WHILE THE COLDEST AIR WILL BEGIN TO PUSH EAST OF THE AREA SATURDAY
HIGHS WILL LIKELY STRUGGLE TO REACH THE MID TEENS AND THEN A SHARP
DROP SATURDAY EVENING IS POSSIBLE BUT DEPENDENT ON HOW FAST CLOUD
COVER ARRIVES WHICH MAY THEN KEEP TEMPS STEADY OR EVEN BEGIN TO
SLOWLY RISE EARLY SUNDAY MORNING. REGARDLESS...TEMPS DURING THIS
TIME PERIOD WILL LIKELY BE IN THE SINGLE DIGITS ALONG WITH WIND
CHILLS BELOW ZERO.

A CLIPPER LIKE SYSTEM WILL QUICKLY MOVE INTO THE AREA SUNDAY
AFTERNOON INTO SUNDAY NIGHT. THIS SYSTEM HAS BEEN FAIRLY
CONSISTENT FOR SEVERAL DAYS...BUT NOW APPEARS TO BE IN A WEAKENING
PHASE AS IT ARRIVES. SO WHILE IT WILL BE COLD ENOUGH THAT PRECIP
SHOULD BE ALL SNOW...FAIRLY LOW CONFIDENCE ON QPF AMOUNTS
ESPECIALLY ACROSS THE EASTERN CWA. CURRENT TRENDS WOULD SUGGEST A
FEW INCHES OF ACCUMULATION WOULD BE POSSIBLE...BUT TOO EARLY FOR
ANY SPECIFICS. TEMPS LOOK TO RISE BACK INTO THE LOW/MID 20S SUNDAY
AND THEN MAY REMAIN GENERALLY STEADY SUNDAY NIGHT INTO MONDAY
MORNING.

MONDAY AND TUESDAY APPEAR GENERALLY DRY WITH A PERIOD OF RAIN OR
SNOW POSSIBLE LATE TUESDAY NIGHT/WEDNESDAY AS WARMER AIR SPREADS
BACK INTO THE REGION THOUGH DIFFERENCES REMAIN BETWEEN THE
ECMWF/GFS. CMS

&&

.AVIATION...
FOR THE 00Z TAFS...

NO SIG CHANGES TO THE GOING FORECAST. FAIRLY QUIET FOR THE AREA
TERMINALS THROUGH TOMORROW. DIURNAL CU/STRATOCU SHOULD DISSIPATE
WITH SUNSET OTHERWISE...CLOUD COVER WILL MAINLY BE BKN CI
ASSOCIATED WITH A STRONG UPPER JET DIVING THROUGH THE MIDDLE
MISSISSIPPI VALLEY. SFC HIGH PRESSURE EXTENDS FROM CNTRL CANADA TO
THE CENTRAL GULF COAST. AS THE AXIS OF THE HIGH PRESSURE MOVES
ACROSS THE TERMINALS TONIGHT...WINDS WILL DIMINISH...AND
EVENTUALLY BACK TO THE WEST/SOUTHWEST THURSDAY. ENHANCED FORCING
UNDER THE UPPER JET STREAM IS HELPING TO GENERATE SOME SNOW
SHOWERS FROM IOWA INTO SOUTHERN ILLINOIS. THE SFC HIGH PRESSURE
WILL MOVE VERY LITTLE THROUGH THE FORECAST PERIOD AND DO NOT
EXPECT ANY OF THE SNOW TO BE ABLE TO SPREAD EAST ENOUGH TO IMPACT
RFD...LET ALONE THE CHICAGO AREA TERMINALS.

KREIN

&&

.MARINE...
202 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT WILL PERSIST
OVER LAKE MICHIGAN THROUGH TONIGHT AHEAD OF A RIDGE THAT STRETCHES
FROM THE NORTHWEST TERRITORIES INTO THE MISSISSIPPI VALLEY.
WINDS OF 30 KT AND FREEZING SPRAY WILL CONTINUE INTO SOME OF THE
OVERNIGHT HOURS THEN SHOULD DIMINISH EARLY THURSDAY AS THE HIGH
INCHES EAST ALLOWING THE GRADIENT TO RELAX. WINDS ALSO BACK TO THE
WEST ON THURSDAY AS THE HIGH BUILDS SOUTH OF LAKE MICHIGAN...THEN
FRESHEN UP AS LOW PRESSURE FORMS OVER ONTARIO. THIS LOW WILL BRING
A REINFORCING SHOT OF COLD AIR SOUTH ON FRIDAY BEHIND A TRAILING
COLD FRONT AND AS A STRONG ARCTIC HIGH BUILDS ACROSS CANADA INTO
THE UPPER MIDWEST. AT LEAST A SHORT WINDOW OF NORTHERLY GALES ARE
EXPECTED BEHIND THE COLD FRONT FRIDAY EVENING OR OVERNIGHT...THEN
WINDS SHOULD GRADUALLY DIMINISH OVER THE WEEKEND AS THE HIGH
BUILDS ACROSS THE GREAT LAKES.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 110310
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
910 PM CST WED FEB 10 2016

.UPDATE...
901 PM CST

SKIES HAVE BEEN SLUGGISH TO THIN THIS EVENING...HOWEVER THE LAST
FEW HOURS IR IMAGERY INDICATES A STEADY EROSION TO THE CLOUDS
ACROSS NORTHERN IL STRETCHING NORTH INTO SOUTHERN WISC. FURTHER
UPSTREAM THERE IS A WEAK MID-LVL VORT THAT WAS SPREADING SOME
CLOUDS ACROSS WESTCENTRAL WISC/NORTHEAST IA...BUT IS EXPECTED TO
CLIP THE WESTERN FORECAST AREA OVERNIGHT...AND EXIT TO THE SOUTH
OF THE FORECAST AREA PRIOR TO DAYBREAK.

HIGH PRESSURE AXIS WLL REMAIN POSITIONED TO THE NORTHWEST OF THE
REGION...HOWEVER WILL SLOWLY SAG SOUTH BY DAYBREAK THUR AND
CONTINUE TO BE PROGRESSIVE AND SLIDE SOUTHEAST OF THE AREA BY FRI
AFTN/EVE. TEMPS OVERNIGHT TONIGHT WILL HOVER AROUND ZERO TO THE
SINGLE DIGITS ABOVE ZERO WEST OF LAKE MICHIGAN...WHILE AREAS
ADJACENT TO THE LAKE WILL LIKELY REMAIN AROUND 5 TO 10 DEGREES
ABOVE ZERO. WHILE WINDS HAVE DIMINISHED A LITTLE THIS
EVENING...WIND CHILL VALUES WILL CONTINUE TO RANGE FROM AROUND
ZERO TO THE SINGLE DIGITS BELOW ZERO. ALONG AND NORTH OF A
LASALLE TO WAUKEGAN LINE WIND CHILL VALUES MAY DIP FURTHER TO -10
TO -15 PRIOR TO DAYBREAK.

BEACHLER

&&

.SHORT TERM...

TONIGHT AND THURSDAY...

248 PM...ONLY CONCERN IS LIGHT LAKE EFFECT SNOW SHOWERS IN FAR
NORTHEAST PORTER COUNTY.

A RIDGE AXIS EXTENDS FROM MN SOUTHEAST TO CENTRAL IL THIS
AFTERNOON AND WILL SLOWLY TURN EASTERLY AS IT BUILDS ACROSS THE
OHIO VALLEY THURSDAY. CURRENT WAVE WITH LIGHT SNOW OVER PARTS OF
IA INTO SOUTHWEST IL WILL REMAIN SOUTHWEST OF THE CWA. WEST/
NORTHWEST WINDS WILL MAINTAIN THE CHANCE OF LAKE EFFECT SNOW
SHOWERS OVER FAR NORTHEAST PORTER COUNTY TONIGHT WITH MINOR NEW
ACCUMULATIONS POSSIBLE. THESE WILL BEGIN TO DIMINISH THURSDAY AS
WINDS TURN MORE WESTERLY. LOW TEMPS TONIGHT WILL DIP INTO THE LOW
SINGLE DIGITS WITH THE USUAL COLD SPOTS POSSIBLY DIPPING BELOW
ZERO. THESE TEMPS WILL COMBINE WITH NORTHWEST WINDS TO ALLOW WIND
CHILL VALUES 10 BELOW ZERO. CMS

&&

.LONG TERM...

THURSDAY NIGHT THROUGH WEDNESDAY...

248 PM...FORECAST CONCERNS INCLUDE LIGHT SNOW FRIDAY MORNING...
WIND CHILLS POSSIBLY REACHING ADVISORY CRITERIA SATURDAY MORNING
AND ANOTHER PERIOD OF LIGHT SNOW SUNDAY AFTERNOON/SUNDAY NIGHT.

ANOTHER SURGE OF VERY COLD AIR WILL ARRIVE FRIDAY AFTERNOON INTO
FRIDAY NIGHT AND AHEAD OF THIS SURGE...THERE WILL BE A PERIOD OF
LIGHT SNOW FRIDAY MORNING. THERE IS SOME DIFFERENCES REGARDING HOW
FAR NORTH THIS LIGHT SNOW WILL OCCUR...WITH THE GFS FURTHEST NORTH
AND ACROSS THE ENTIRE AREA. BEST CHANCES FOR LIGHT SNOW ALONG WITH
ANY MINOR ACCUMULATIONS APPEAR TO REMAIN ACROSS THE SOUTHERN CWA
AND MAINTAINED LOW CHANCE POPS FOR NOW. BUT AS TRENDS EMERGE...
HIGHER POPS MAY BE NEEDED DESPITE THE LOW QPF EXPECTED. TEMPS ALSO
APPEAR TO HOLD FAIRLY STEADY THURSDAY NIGHT INTO FRIDAY OR PERHAPS
AN EVENING LOW THEN STEADY OR SLOWLY RISING INTO FRIDAY MORNING.

AS THE COLDER AIR ARRIVES FRIDAY AFTERNOON...TEMPS WILL BEGIN TO
FALL WITH LOWS LIKELY BELOW ZERO ACROSS MUCH OF NORTHWEST IL BY
SATURDAY MORNING AND ONLY LOW SINGLE DIGITS ELSEWHERE. NORTHWEST
WINDS WILL ALSO BECOME STRONG/GUSTY FRIDAY AFTERNOON/EVENING WITH
GUSTS PERHAPS INTO THE 30 MPH RANGE. WIND CHILLS WILL LIKELY FALL
BELOW ZERO BY EARLY FRIDAY EVENING AND INTO THE 15 BELOW TO 25
BELOW ZERO RANGE SATURDAY MORNING.

WHILE THE COLDEST AIR WILL BEGIN TO PUSH EAST OF THE AREA SATURDAY
HIGHS WILL LIKELY STRUGGLE TO REACH THE MID TEENS AND THEN A SHARP
DROP SATURDAY EVENING IS POSSIBLE BUT DEPENDENT ON HOW FAST CLOUD
COVER ARRIVES WHICH MAY THEN KEEP TEMPS STEADY OR EVEN BEGIN TO
SLOWLY RISE EARLY SUNDAY MORNING. REGARDLESS...TEMPS DURING THIS
TIME PERIOD WILL LIKELY BE IN THE SINGLE DIGITS ALONG WITH WIND
CHILLS BELOW ZERO.

A CLIPPER LIKE SYSTEM WILL QUICKLY MOVE INTO THE AREA SUNDAY
AFTERNOON INTO SUNDAY NIGHT. THIS SYSTEM HAS BEEN FAIRLY
CONSISTENT FOR SEVERAL DAYS...BUT NOW APPEARS TO BE IN A WEAKENING
PHASE AS IT ARRIVES. SO WHILE IT WILL BE COLD ENOUGH THAT PRECIP
SHOULD BE ALL SNOW...FAIRLY LOW CONFIDENCE ON QPF AMOUNTS
ESPECIALLY ACROSS THE EASTERN CWA. CURRENT TRENDS WOULD SUGGEST A
FEW INCHES OF ACCUMULATION WOULD BE POSSIBLE...BUT TOO EARLY FOR
ANY SPECIFICS. TEMPS LOOK TO RISE BACK INTO THE LOW/MID 20S SUNDAY
AND THEN MAY REMAIN GENERALLY STEADY SUNDAY NIGHT INTO MONDAY
MORNING.

MONDAY AND TUESDAY APPEAR GENERALLY DRY WITH A PERIOD OF RAIN OR
SNOW POSSIBLE LATE TUESDAY NIGHT/WEDNESDAY AS WARMER AIR SPREADS
BACK INTO THE REGION THOUGH DIFFERENCES REMAIN BETWEEN THE
ECMWF/GFS. CMS

&&

.AVIATION...
FOR THE 00Z TAFS...

NO SIG CHANGES TO THE GOING FORECAST. FAIRLY QUIET FOR THE AREA
TERMINALS THROUGH TOMORROW. DIURNAL CU/STRATOCU SHOULD DISSIPATE
WITH SUNSET OTHERWISE...CLOUD COVER WILL MAINLY BE BKN CI
ASSOCIATED WITH A STRONG UPPER JET DIVING THROUGH THE MIDDLE
MISSISSIPPI VALLEY. SFC HIGH PRESSURE EXTENDS FROM CNTRL CANADA TO
THE CENTRAL GULF COAST. AS THE AXIS OF THE HIGH PRESSURE MOVES
ACROSS THE TERMINALS TONIGHT...WINDS WILL DIMINISH...AND
EVENTUALLY BACK TO THE WEST/SOUTHWEST THURSDAY. ENHANCED FORCING
UNDER THE UPPER JET STREAM IS HELPING TO GENERATE SOME SNOW
SHOWERS FROM IOWA INTO SOUTHERN ILLINOIS. THE SFC HIGH PRESSURE
WILL MOVE VERY LITTLE THROUGH THE FORECAST PERIOD AND DO NOT
EXPECT ANY OF THE SNOW TO BE ABLE TO SPREAD EAST ENOUGH TO IMPACT
RFD...LET ALONE THE CHICAGO AREA TERMINALS.

KREIN

&&

.MARINE...
202 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT WILL PERSIST
OVER LAKE MICHIGAN THROUGH TONIGHT AHEAD OF A RIDGE THAT STRETCHES
FROM THE NORTHWEST TERRITORIES INTO THE MISSISSIPPI VALLEY.
WINDS OF 30 KT AND FREEZING SPRAY WILL CONTINUE INTO SOME OF THE
OVERNIGHT HOURS THEN SHOULD DIMINISH EARLY THURSDAY AS THE HIGH
INCHES EAST ALLOWING THE GRADIENT TO RELAX. WINDS ALSO BACK TO THE
WEST ON THURSDAY AS THE HIGH BUILDS SOUTH OF LAKE MICHIGAN...THEN
FRESHEN UP AS LOW PRESSURE FORMS OVER ONTARIO. THIS LOW WILL BRING
A REINFORCING SHOT OF COLD AIR SOUTH ON FRIDAY BEHIND A TRAILING
COLD FRONT AND AS A STRONG ARCTIC HIGH BUILDS ACROSS CANADA INTO
THE UPPER MIDWEST. AT LEAST A SHORT WINDOW OF NORTHERLY GALES ARE
EXPECTED BEHIND THE COLD FRONT FRIDAY EVENING OR OVERNIGHT...THEN
WINDS SHOULD GRADUALLY DIMINISH OVER THE WEEKEND AS THE HIGH
BUILDS ACROSS THE GREAT LAKES.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 102333
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
533 PM CST WED FEB 10 2016

.SHORT TERM...

TONIGHT AND THURSDAY...

248 PM...ONLY CONCERN IS LIGHT LAKE EFFECT SNOW SHOWERS IN FAR
NORTHEAST PORTER COUNTY.

A RIDGE AXIS EXTENDS FROM MN SOUTHEAST TO CENTRAL IL THIS
AFTERNOON AND WILL SLOWLY TURN EASTERLY AS IT BUILDS ACROSS THE
OHIO VALLEY THURSDAY. CURRENT WAVE WITH LIGHT SNOW OVER PARTS OF
IA INTO SOUTHWEST IL WILL REMAIN SOUTHWEST OF THE CWA. WEST/
NORTHWEST WINDS WILL MAINTAIN THE CHANCE OF LAKE EFFECT SNOW
SHOWERS OVER FAR NORTHEAST PORTER COUNTY TONIGHT WITH MINOR NEW
ACCUMULATIONS POSSIBLE. THESE WILL BEGIN TO DIMINISH THURSDAY AS
WINDS TURN MORE WESTERLY. LOW TEMPS TONIGHT WILL DIP INTO THE LOW
SINGLE DIGITS WITH THE USUAL COLD SPOTS POSSIBLY DIPPING BELOW
ZERO. THESE TEMPS WILL COMBINE WITH NORTHWEST WINDS TO ALLOW WIND
CHILL VALUES 10 BELOW ZERO. CMS

&&

.LONG TERM...

THURSDAY NIGHT THROUGH WEDNESDAY...

248 PM...FORECAST CONCERNS INCLUDE LIGHT SNOW FRIDAY MORNING...
WIND CHILLS POSSIBLY REACHING ADVISORY CRITERIA SATURDAY MORNING
AND ANOTHER PERIOD OF LIGHT SNOW SUNDAY AFTERNOON/SUNDAY NIGHT.

ANOTHER SURGE OF VERY COLD AIR WILL ARRIVE FRIDAY AFTERNOON INTO
FRIDAY NIGHT AND AHEAD OF THIS SURGE...THERE WILL BE A PERIOD OF
LIGHT SNOW FRIDAY MORNING. THERE IS SOME DIFFERENCES REGARDING HOW
FAR NORTH THIS LIGHT SNOW WILL OCCUR...WITH THE GFS FURTHEST NORTH
AND ACROSS THE ENTIRE AREA. BEST CHANCES FOR LIGHT SNOW ALONG WITH
ANY MINOR ACCUMULATIONS APPEAR TO REMAIN ACROSS THE SOUTHERN CWA
AND MAINTAINED LOW CHANCE POPS FOR NOW. BUT AS TRENDS EMERGE...
HIGHER POPS MAY BE NEEDED DESPITE THE LOW QPF EXPECTED. TEMPS ALSO
APPEAR TO HOLD FAIRLY STEADY THURSDAY NIGHT INTO FRIDAY OR PERHAPS
AN EVENING LOW THEN STEADY OR SLOWLY RISING INTO FRIDAY MORNING.

AS THE COLDER AIR ARRIVES FRIDAY AFTERNOON...TEMPS WILL BEGIN TO
FALL WITH LOWS LIKELY BELOW ZERO ACROSS MUCH OF NORTHWEST IL BY
SATURDAY MORNING AND ONLY LOW SINGLE DIGITS ELSEWHERE. NORTHWEST
WINDS WILL ALSO BECOME STRONG/GUSTY FRIDAY AFTERNOON/EVENING WITH
GUSTS PERHAPS INTO THE 30 MPH RANGE. WIND CHILLS WILL LIKELY FALL
BELOW ZERO BY EARLY FRIDAY EVENING AND INTO THE 15 BELOW TO 25
BELOW ZERO RANGE SATURDAY MORNING.

WHILE THE COLDEST AIR WILL BEGIN TO PUSH EAST OF THE AREA SATURDAY
HIGHS WILL LIKELY STRUGGLE TO REACH THE MID TEENS AND THEN A SHARP
DROP SATURDAY EVENING IS POSSIBLE BUT DEPENDENT ON HOW FAST CLOUD
COVER ARRIVES WHICH MAY THEN KEEP TEMPS STEADY OR EVEN BEGIN TO
SLOWLY RISE EARLY SUNDAY MORNING. REGARDLESS...TEMPS DURING THIS
TIME PERIOD WILL LIKELY BE IN THE SINGLE DIGITS ALONG WITH WIND
CHILLS BELOW ZERO.

A CLIPPER LIKE SYSTEM WILL QUICKLY MOVE INTO THE AREA SUNDAY
AFTERNOON INTO SUNDAY NIGHT. THIS SYSTEM HAS BEEN FAIRLY
CONSISTENT FOR SEVERAL DAYS...BUT NOW APPEARS TO BE IN A WEAKENING
PHASE AS IT ARRIVES. SO WHILE IT WILL BE COLD ENOUGH THAT PRECIP
SHOULD BE ALL SNOW...FAIRLY LOW CONFIDENCE ON QPF AMOUNTS
ESPECIALLY ACROSS THE EASTERN CWA. CURRENT TRENDS WOULD SUGGEST A
FEW INCHES OF ACCUMULATION WOULD BE POSSIBLE...BUT TOO EARLY FOR
ANY SPECIFICS. TEMPS LOOK TO RISE BACK INTO THE LOW/MID 20S SUNDAY
AND THEN MAY REMAIN GENERALLY STEADY SUNDAY NIGHT INTO MONDAY
MORNING.

MONDAY AND TUESDAY APPEAR GENERALLY DRY WITH A PERIOD OF RAIN OR
SNOW POSSIBLE LATE TUESDAY NIGHT/WEDNESDAY AS WARMER AIR SPREADS
BACK INTO THE REGION THOUGH DIFFERENCES REMAIN BETWEEN THE
ECMWF/GFS. CMS

&&

.AVIATION...
FOR THE 00Z TAFS...

NO SIG CHANGES TO THE GOING FORECAST. FAIRLY QUIET FOR THE AREA
TERMINALS THROUGH TOMORROW. DIURNAL CU/STRATOCU SHOULD DISSIPATE
WITH SUNSET OTHERWISE...CLOUD COVER WILL MAINLY BE BKN CI
ASSOCIATED WITH A STRONG UPPER JET DIVING THROUGH THE MIDDLE
MISSISSIPPI VALLEY. SFC HIGH PRESSURE EXTENDS FROM CNTRL CANADA TO
THE CENTRAL GULF COAST. AS THE AXIS OF THE HIGH PRESSURE MOVES
ACROSS THE TERMINALS TONIGHT...WINDS WILL DIMINISH...AND
EVENTUALLY BACK TO THE WEST/SOUTHWEST THURSDAY. ENHANCED FORCING
UNDER THE UPPER JET STREAM IS HELPING TO GENERATE SOME SNOW
SHOWERS FROM IOWA INTO SOUTHERN ILLINOIS. THE SFC HIGH PRESSURE
WILL MOVE VERY LITTLE THROUGH THE FORECAST PERIOD AND DO NOT
EXPECT ANY OF THE SNOW TO BE ABLE TO SPREAD EAST ENOUGH TO IMPACT
RFD...LET ALONE THE CHICAGO AREA TERMINALS.

KREIN

&&

.MARINE...
202 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT WILL PERSIST
OVER LAKE MICHIGAN THROUGH TONIGHT AHEAD OF A RIDGE THAT STRETCHES
FROM THE NORTHWEST TERRITORIES INTO THE MISSISSIPPI VALLEY.
WINDS OF 30 KT AND FREEZING SPRAY WILL CONTINUE INTO SOME OF THE
OVERNIGHT HOURS THEN SHOULD DIMINISH EARLY THURSDAY AS THE HIGH
INCHES EAST ALLOWING THE GRADIENT TO RELAX. WINDS ALSO BACK TO THE
WEST ON THURSDAY AS THE HIGH BUILDS SOUTH OF LAKE MICHIGAN...THEN
FRESHEN UP AS LOW PRESSURE FORMS OVER ONTARIO. THIS LOW WILL BRING
A REINFORCING SHOT OF COLD AIR SOUTH ON FRIDAY BEHIND A TRAILING
COLD FRONT AND AS A STRONG ARCTIC HIGH BUILDS ACROSS CANADA INTO
THE UPPER MIDWEST. AT LEAST A SHORT WINDOW OF NORTHERLY GALES ARE
EXPECTED BEHIND THE COLD FRONT FRIDAY EVENING OR OVERNIGHT...THEN
WINDS SHOULD GRADUALLY DIMINISH OVER THE WEEKEND AS THE HIGH
BUILDS ACROSS THE GREAT LAKES.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 102333
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
533 PM CST WED FEB 10 2016

.SHORT TERM...

TONIGHT AND THURSDAY...

248 PM...ONLY CONCERN IS LIGHT LAKE EFFECT SNOW SHOWERS IN FAR
NORTHEAST PORTER COUNTY.

A RIDGE AXIS EXTENDS FROM MN SOUTHEAST TO CENTRAL IL THIS
AFTERNOON AND WILL SLOWLY TURN EASTERLY AS IT BUILDS ACROSS THE
OHIO VALLEY THURSDAY. CURRENT WAVE WITH LIGHT SNOW OVER PARTS OF
IA INTO SOUTHWEST IL WILL REMAIN SOUTHWEST OF THE CWA. WEST/
NORTHWEST WINDS WILL MAINTAIN THE CHANCE OF LAKE EFFECT SNOW
SHOWERS OVER FAR NORTHEAST PORTER COUNTY TONIGHT WITH MINOR NEW
ACCUMULATIONS POSSIBLE. THESE WILL BEGIN TO DIMINISH THURSDAY AS
WINDS TURN MORE WESTERLY. LOW TEMPS TONIGHT WILL DIP INTO THE LOW
SINGLE DIGITS WITH THE USUAL COLD SPOTS POSSIBLY DIPPING BELOW
ZERO. THESE TEMPS WILL COMBINE WITH NORTHWEST WINDS TO ALLOW WIND
CHILL VALUES 10 BELOW ZERO. CMS

&&

.LONG TERM...

THURSDAY NIGHT THROUGH WEDNESDAY...

248 PM...FORECAST CONCERNS INCLUDE LIGHT SNOW FRIDAY MORNING...
WIND CHILLS POSSIBLY REACHING ADVISORY CRITERIA SATURDAY MORNING
AND ANOTHER PERIOD OF LIGHT SNOW SUNDAY AFTERNOON/SUNDAY NIGHT.

ANOTHER SURGE OF VERY COLD AIR WILL ARRIVE FRIDAY AFTERNOON INTO
FRIDAY NIGHT AND AHEAD OF THIS SURGE...THERE WILL BE A PERIOD OF
LIGHT SNOW FRIDAY MORNING. THERE IS SOME DIFFERENCES REGARDING HOW
FAR NORTH THIS LIGHT SNOW WILL OCCUR...WITH THE GFS FURTHEST NORTH
AND ACROSS THE ENTIRE AREA. BEST CHANCES FOR LIGHT SNOW ALONG WITH
ANY MINOR ACCUMULATIONS APPEAR TO REMAIN ACROSS THE SOUTHERN CWA
AND MAINTAINED LOW CHANCE POPS FOR NOW. BUT AS TRENDS EMERGE...
HIGHER POPS MAY BE NEEDED DESPITE THE LOW QPF EXPECTED. TEMPS ALSO
APPEAR TO HOLD FAIRLY STEADY THURSDAY NIGHT INTO FRIDAY OR PERHAPS
AN EVENING LOW THEN STEADY OR SLOWLY RISING INTO FRIDAY MORNING.

AS THE COLDER AIR ARRIVES FRIDAY AFTERNOON...TEMPS WILL BEGIN TO
FALL WITH LOWS LIKELY BELOW ZERO ACROSS MUCH OF NORTHWEST IL BY
SATURDAY MORNING AND ONLY LOW SINGLE DIGITS ELSEWHERE. NORTHWEST
WINDS WILL ALSO BECOME STRONG/GUSTY FRIDAY AFTERNOON/EVENING WITH
GUSTS PERHAPS INTO THE 30 MPH RANGE. WIND CHILLS WILL LIKELY FALL
BELOW ZERO BY EARLY FRIDAY EVENING AND INTO THE 15 BELOW TO 25
BELOW ZERO RANGE SATURDAY MORNING.

WHILE THE COLDEST AIR WILL BEGIN TO PUSH EAST OF THE AREA SATURDAY
HIGHS WILL LIKELY STRUGGLE TO REACH THE MID TEENS AND THEN A SHARP
DROP SATURDAY EVENING IS POSSIBLE BUT DEPENDENT ON HOW FAST CLOUD
COVER ARRIVES WHICH MAY THEN KEEP TEMPS STEADY OR EVEN BEGIN TO
SLOWLY RISE EARLY SUNDAY MORNING. REGARDLESS...TEMPS DURING THIS
TIME PERIOD WILL LIKELY BE IN THE SINGLE DIGITS ALONG WITH WIND
CHILLS BELOW ZERO.

A CLIPPER LIKE SYSTEM WILL QUICKLY MOVE INTO THE AREA SUNDAY
AFTERNOON INTO SUNDAY NIGHT. THIS SYSTEM HAS BEEN FAIRLY
CONSISTENT FOR SEVERAL DAYS...BUT NOW APPEARS TO BE IN A WEAKENING
PHASE AS IT ARRIVES. SO WHILE IT WILL BE COLD ENOUGH THAT PRECIP
SHOULD BE ALL SNOW...FAIRLY LOW CONFIDENCE ON QPF AMOUNTS
ESPECIALLY ACROSS THE EASTERN CWA. CURRENT TRENDS WOULD SUGGEST A
FEW INCHES OF ACCUMULATION WOULD BE POSSIBLE...BUT TOO EARLY FOR
ANY SPECIFICS. TEMPS LOOK TO RISE BACK INTO THE LOW/MID 20S SUNDAY
AND THEN MAY REMAIN GENERALLY STEADY SUNDAY NIGHT INTO MONDAY
MORNING.

MONDAY AND TUESDAY APPEAR GENERALLY DRY WITH A PERIOD OF RAIN OR
SNOW POSSIBLE LATE TUESDAY NIGHT/WEDNESDAY AS WARMER AIR SPREADS
BACK INTO THE REGION THOUGH DIFFERENCES REMAIN BETWEEN THE
ECMWF/GFS. CMS

&&

.AVIATION...
FOR THE 00Z TAFS...

NO SIG CHANGES TO THE GOING FORECAST. FAIRLY QUIET FOR THE AREA
TERMINALS THROUGH TOMORROW. DIURNAL CU/STRATOCU SHOULD DISSIPATE
WITH SUNSET OTHERWISE...CLOUD COVER WILL MAINLY BE BKN CI
ASSOCIATED WITH A STRONG UPPER JET DIVING THROUGH THE MIDDLE
MISSISSIPPI VALLEY. SFC HIGH PRESSURE EXTENDS FROM CNTRL CANADA TO
THE CENTRAL GULF COAST. AS THE AXIS OF THE HIGH PRESSURE MOVES
ACROSS THE TERMINALS TONIGHT...WINDS WILL DIMINISH...AND
EVENTUALLY BACK TO THE WEST/SOUTHWEST THURSDAY. ENHANCED FORCING
UNDER THE UPPER JET STREAM IS HELPING TO GENERATE SOME SNOW
SHOWERS FROM IOWA INTO SOUTHERN ILLINOIS. THE SFC HIGH PRESSURE
WILL MOVE VERY LITTLE THROUGH THE FORECAST PERIOD AND DO NOT
EXPECT ANY OF THE SNOW TO BE ABLE TO SPREAD EAST ENOUGH TO IMPACT
RFD...LET ALONE THE CHICAGO AREA TERMINALS.

KREIN

&&

.MARINE...
202 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT WILL PERSIST
OVER LAKE MICHIGAN THROUGH TONIGHT AHEAD OF A RIDGE THAT STRETCHES
FROM THE NORTHWEST TERRITORIES INTO THE MISSISSIPPI VALLEY.
WINDS OF 30 KT AND FREEZING SPRAY WILL CONTINUE INTO SOME OF THE
OVERNIGHT HOURS THEN SHOULD DIMINISH EARLY THURSDAY AS THE HIGH
INCHES EAST ALLOWING THE GRADIENT TO RELAX. WINDS ALSO BACK TO THE
WEST ON THURSDAY AS THE HIGH BUILDS SOUTH OF LAKE MICHIGAN...THEN
FRESHEN UP AS LOW PRESSURE FORMS OVER ONTARIO. THIS LOW WILL BRING
A REINFORCING SHOT OF COLD AIR SOUTH ON FRIDAY BEHIND A TRAILING
COLD FRONT AND AS A STRONG ARCTIC HIGH BUILDS ACROSS CANADA INTO
THE UPPER MIDWEST. AT LEAST A SHORT WINDOW OF NORTHERLY GALES ARE
EXPECTED BEHIND THE COLD FRONT FRIDAY EVENING OR OVERNIGHT...THEN
WINDS SHOULD GRADUALLY DIMINISH OVER THE WEEKEND AS THE HIGH
BUILDS ACROSS THE GREAT LAKES.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 102048
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
248 PM CST WED FEB 10 2016

.SHORT TERM...

TONIGHT AND THURSDAY...

248 PM...ONLY CONCERN IS LIGHT LAKE EFFECT SNOW SHOWERS IN FAR
NORTHEAST PORTER COUNTY.

A RIDGE AXIS EXTENDS FROM MN SOUTHEAST TO CENTRAL IL THIS
AFTERNOON AND WILL SLOWLY TURN EASTERLY AS IT BUILDS ACROSS THE
OHIO VALLEY THURSDAY. CURRENT WAVE WITH LIGHT SNOW OVER PARTS OF
IA INTO SOUTHWEST IL WILL REMAIN SOUTHWEST OF THE CWA. WEST/
NORTHWEST WINDS WILL MAINTAIN THE CHANCE OF LAKE EFFECT SNOW
SHOWERS OVER FAR NORTHEAST PORTER COUNTY TONIGHT WITH MINOR NEW
ACCUMULATIONS POSSIBLE. THESE WILL BEGIN TO DIMINISH THURSDAY AS
WINDS TURN MORE WESTERLY. LOW TEMPS TONIGHT WILL DIP INTO THE LOW
SINGLE DIGITS WITH THE USUAL COLD SPOTS POSSIBLY DIPPING BELOW
ZERO. THESE TEMPS WILL COMBINE WITH NORTHWEST WINDS TO ALLOW WIND
CHILL VALUES 10 BELOW ZERO. CMS

&&

.LONG TERM...

THURSDAY NIGHT THROUGH WEDNESDAY...

248 PM...FORECAST CONCERNS INCLUDE LIGHT SNOW FRIDAY MORNING...
WIND CHILLS POSSIBLY REACHING ADVISORY CRITERIA SATURDAY MORNING
AND ANOTHER PERIOD OF LIGHT SNOW SUNDAY AFTERNOON/SUNDAY NIGHT.

ANOTHER SURGE OF VERY COLD AIR WILL ARRIVE FRIDAY AFTERNOON INTO
FRIDAY NIGHT AND AHEAD OF THIS SURGE...THERE WILL BE A PERIOD OF
LIGHT SNOW FRIDAY MORNING. THERE IS SOME DIFFERENCES REGARDING HOW
FAR NORTH THIS LIGHT SNOW WILL OCCUR...WITH THE GFS FURTHEST NORTH
AND ACROSS THE ENTIRE AREA. BEST CHANCES FOR LIGHT SNOW ALONG WITH
ANY MINOR ACCUMULATIONS APPEAR TO REMAIN ACROSS THE SOUTHERN CWA
AND MAINTAINED LOW CHANCE POPS FOR NOW. BUT AS TRENDS EMERGE...
HIGHER POPS MAY BE NEEDED DESPITE THE LOW QPF EXPECTED. TEMPS ALSO
APPEAR TO HOLD FAIRLY STEADY THURSDAY NIGHT INTO FRIDAY OR PERHAPS
AN EVENING LOW THEN STEADY OR SLOWLY RISING INTO FRIDAY MORNING.

AS THE COLDER AIR ARRIVES FRIDAY AFTERNOON...TEMPS WILL BEGIN TO
FALL WITH LOWS LIKELY BELOW ZERO ACROSS MUCH OF NORTHWEST IL BY
SATURDAY MORNING AND ONLY LOW SINGLE DIGITS ELSEWHERE. NORTHWEST
WINDS WILL ALSO BECOME STRONG/GUSTY FRIDAY AFTERNOON/EVENING WITH
GUSTS PERHAPS INTO THE 30 MPH RANGE. WIND CHILLS WILL LIKELY FALL
BELOW ZERO BY EARLY FRIDAY EVENING AND INTO THE 15 BELOW TO 25
BELOW ZERO RANGE SATURDAY MORNING.

WHILE THE COLDEST AIR WILL BEGIN TO PUSH EAST OF THE AREA SATURDAY
HIGHS WILL LIKELY STRUGGLE TO REACH THE MID TEENS AND THEN A SHARP
DROP SATURDAY EVENING IS POSSIBLE BUT DEPENDENT ON HOW FAST CLOUD
COVER ARRIVES WHICH MAY THEN KEEP TEMPS STEADY OR EVEN BEGIN TO
SLOWLY RISE EARLY SUNDAY MORNING. REGARDLESS...TEMPS DURING THIS
TIME PERIOD WILL LIKELY BE IN THE SINGLE DIGITS ALONG WITH WIND
CHILLS BELOW ZERO.

A CLIPPER LIKE SYSTEM WILL QUICKLY MOVE INTO THE AREA SUNDAY
AFTERNOON INTO SUNDAY NIGHT. THIS SYSTEM HAS BEEN FAIRLY
CONSISTENT FOR SEVERAL DAYS...BUT NOW APPEARS TO BE IN A WEAKENING
PHASE AS IT ARRIVES. SO WHILE IT WILL BE COLD ENOUGH THAT PRECIP
SHOULD BE ALL SNOW...FAIRLY LOW CONFIDENCE ON QPF AMOUNTS
ESPECIALLY ACROSS THE EASTERN CWA. CURRENT TRENDS WOULD SUGGEST A
FEW INCHES OF ACCUMULATION WOULD BE POSSIBLE...BUT TOO EARLY FOR
ANY SPECIFICS. TEMPS LOOK TO RISE BACK INTO THE LOW/MID 20S SUNDAY
AND THEN MAY REMAIN GENERALLY STEADY SUNDAY NIGHT INTO MONDAY
MORNING.

MONDAY AND TUESDAY APPEAR GENERALLY DRY WITH A PERIOD OF RAIN OR
SNOW POSSIBLE LATE TUESDAY NIGHT/WEDNESDAY AS WARMER AIR SPREADS
BACK INTO THE REGION THOUGH DIFFERENCES REMAIN BETWEEN THE
ECMWF/GFS. CMS

&&

.AVIATION...
FOR THE 18Z TAFS...

FAIRLY QUIET FORECAST ON TAP FOR THE CHICAGO/ROCKFORD AREA
TERMINALS THROUGH TOMORROW. AREA OF THIN OVERCAST STRATUS THAT
WAS IN PLACE THIS MORNING HAS BECOME SCT-BKN THIS HOUR AND EXPECT
PRIMARILY VFR CONDITIONS TO PREVAIL THROUGH REMAINDER OF THE
FORECAST PERIOD. RIDGE OF HIGH PRESSURE CURRENTLY STRETCHES FROM
THE LOWER TO UPPER MISSISSIPPI VALLEY AND WILL INCH TOWARDS THE
TERMINALS ALLOWING WINDS TO DIMINISH...AND EVENTUALLY BACK TO THE
WEST/SOUTHWEST THURSDAY. AN AREA OF LOW PRESSURE IS PROGGED TO
MOVE FROM THE PLAINS INTO THE LOWER MISSISSIPPI VALLEY TONIGHT
RESULTING IN AN INCREASE IN MAINLY UPPER LEVEL CLOUD
COVER...THOUGH ANY PRECIP WITH THIS SYSTEM WILL STAY WELL TO OUR
WEST AND SOUTH.

BMD

&&

.MARINE...
202 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT WILL PERSIST
OVER LAKE MICHIGAN THROUGH TONIGHT AHEAD OF A RIDGE THAT STRETCHES
FROM THE NORTHWEST TERRITORIES INTO THE MISSISSIPPI VALLEY.
WINDS OF 30 KT AND FREEZING SPRAY WILL CONTINUE INTO SOME OF THE
OVERNIGHT HOURS THEN SHOULD DIMINISH EARLY THURSDAY AS THE HIGH
INCHES EAST ALLOWING THE GRADIENT TO RELAX. WINDS ALSO BACK TO THE
WEST ON THURSDAY AS THE HIGH BUILDS SOUTH OF LAKE MICHIGAN...THEN
FRESHEN UP AS LOW PRESSURE FORMS OVER ONTARIO. THIS LOW WILL BRING
A REINFORCING SHOT OF COLD AIR SOUTH ON FRIDAY BEHIND A TRAILING
COLD FRONT AND AS A STRONG ARCTIC HIGH BUILDS ACROSS CANADA INTO
THE UPPER MIDWEST. AT LEAST A SHORT WINDOW OF NORTHERLY GALES ARE
EXPECTED BEHIND THE COLD FRONT FRIDAY EVENING OR OVERNIGHT...THEN
WINDS SHOULD GRADUALLY DIMINISH OVER THE WEEKEND AS THE HIGH
BUILDS ACROSS THE GREAT LAKES.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM
     THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 102004
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
204 PM CST WED FEB 10 2016

.SHORT TERM...
331 AM CST

THROUGH TONIGHT...

THE MESSAGE FOR THE REMAINDER OF THE WEEK AND THIS WEEKEND IS
SIMPLY UNSEASONABLY COLD. EARLY MORNING LOWS MAY DIP TO SUBZERO IN
OUTLYING LOCATIONS THURSDAY MORNING THEN AGAIN SATURDAY AND SUNDAY
MORNINGS. AT THIS TIME IT APPEARS FOR THE MOST PART WIND CHILLS
SHOULD REMAIN ABOVE OUR CRITERIA OF ADVISORY /WHICH IS AOB
-15F/...THOUGH COULD DIP TO THAT LEVEL LATER FRIDAY NIGHT AND
SATURDAY MORNING. NO MAJOR SNOW CHANCES EXIST THROUGH
SATURDAY...THOUGH CONTINUING TO SEE A TREND FOR PART OF NORTHWEST
INDIANA TO SEE SOME LAKE EFFECT SNOW FRIDAY NIGHT AND SATURDAY.

THE HIGHLY AMPLIFIED LONG WAVE TROUGH OVER EASTERN NORTH AMERICA
IS FINALLY SHIFTING ITS WAY EASTWARD. UPPER TROPOSPHERIC NORTHERLY
FLOW BEHIND THIS WILL KEEP THE COLD PATTERN IN PLACE THOUGH WITH A
MODIFIED ARCTIC AIR MASS HAVING SPREAD INTO THE REGION. THE MIXED
LAYER WILL WARM LITTLE TODAY WITH 925MB TEMPERATURES AROUND -16C.
THIS PROFILE AND UPSTREAM TEMPERATURES YESTERDAY LOOK TO SUPPORT
MID TEENS FOR HIGHS. THE CLOUD FORECAST FOR TODAY IS CHALLENGING
AS OFTEN CAN BE THE CASE AT THE PERIPHERY OF DEPARTING CYCLONIC
FLOW. EXPECT THAT EARLY MORNING HOLES WILL FILL IN DURING MIDDAY
WITH THE CONTINUED STEEP LAPSE RATES. DRY ADVECTION HAS BROUGHT
DEW POINTS TO AROUND OR EVEN BELOW ZERO INTO THE FORECAST
AREA...SO THE CLOUDS ARE LIKELY TO BE THIN. THESE SHOULD ADVECT
AWAY TONIGHT. COMBINED WITH WEAKENING WINDS AND A LIGHT BUT FRESH
SNOW IN PLACES...THE CLEAR NIGHT WILL SEE LOWER TO MID SINGLE
DIGITS IN MOST LOCATIONS WITH THE SUBZERO LOWS POSSIBLE IN THE
USUAL COLDER SPOTS.

MTF

&&

.LONG TERM...
331 AM CST

THURSDAY THROUGH WEDNESDAY...

HIGH PRESSURE AT THE SURFACE WILL PREVAIL THURSDAY INTO THURSDAY
NIGHT WITH THE DAYTIME HOURS OF THURSDAY LIKELY TO BE PRIMARILY
SUNNY AND ASSISTING IN A WEE BIT OF TEMPERATURE MODERATION. MODEL
GUIDANCE CONTINUES TO INDICATE A SHEARED SHORT WAVE TROUGH DIVING
SOUTHEAST FROM THE UPPER PLAINS TO THE LOWER OHIO VALLEY THURSDAY
NIGHT INTO FRIDAY. THIS IS BASICALLY RIDING THE ELEVATED
BAROCLINIC ZONE SIMILAR TO A SYSTEM TODAY OFF TO OUR SOUTHWEST.
CONTINUE TO THINK MOST SNOW WITH THIS WILL REMAIN SOUTH. FRIDAY
SHOULD BE CLOUDY THOUGH AND MAYBE ENOUGH WEAK ISENTROPIC ASCENT
FOR SOME FLURRIES.

THAT SHORT WAVE AND JET WITH REINFORCE THE COLD AIR INTO THE
REGION...BRINGING THE ARCTIC COLD FRONT BACK SOUTH FRIDAY
AFTERNOON OR EVENING. THIS SETS UP THE COLD WEEKEND PARTICULARLY
SATURDAY. WHILE AGAIN SOME FLURRIES MAY BE SEEN WITH THIS...MOST
OF THE AREA SHOULD BE DRY. THE EXCEPTION IS FAR NORTHWEST INDIANA
WHERE BOUNDARY LAYER FLOW IS LIKELY TO TURN MORE NORTHERLY WITH A
DEEP LOW FAVORED OFF THE NORTHEAST U.S. AND A 1040MB+ HIGH TO THE
WEST. FORECAST EQUILIBRIUM LEVELS FROM THE GFS ARE OVER 10000
FT...BUT MOISTURE MAY BE DRY ENOUGH THAT COVERAGE OF ANY LAKE
EFFECT SNOW SHOWERS MAY BE IN SINGLE BAND/S/. TOO EARLY YET TO
TELL IF THERE WILL BE VERY FOCUSED CONVERGENCE OR EVEN IF SNOW
SHOWERS WILL ROTATE BACK TO THE WEST FAR ENOUGH TO IMPACT PORTER
AND LAKE COUNTIES.

GLOBAL GUIDANCE HAS INDICATED A PACIFIC/CLIPPER HYBRID SYSTEM
CROSSING THE GENERAL REGION SOMETIME LATE IN THE WEEKEND/EARLY
NEXT WEEK. CONFIDENCE IN THIS SYSTEM IS LOW AND IT CERTAINLY COULD
SLOW TOO. EVEN IF THAT WERE TO HAPPEN THE COLD AIR IN ADVANCE
LOOKS LIKE THE PROFILES SHOULD BE COOL ENOUGH TO SUPPORT SNOW. HOW
MUCH IF ANY SNOW THOUGH WILL DEPEND ON ITS EXACT TRACK WHICH COULD
VARY SIGNIFICANTLY YET FOR SEVERAL MODEL RUNS.

MTF

&&

.AVIATION...
FOR THE 18Z TAFS...

FAIRLY QUIET FORECAST ON TAP FOR THE CHICAGO/ROCKFORD AREA
TERMINALS THROUGH TOMORROW. AREA OF THIN OVERCAST STRATUS THAT
WAS IN PLACE THIS MORNING HAS BECOME SCT-BKN THIS HOUR AND EXPECT
PRIMARILY VFR CONDITIONS TO PREVAIL THROUGH REMAINDER OF THE
FORECAST PERIOD. RIDGE OF HIGH PRESSURE CURRENTLY STRETCHES FROM
THE LOWER TO UPPER MISSISSIPPI VALLEY AND WILL INCH TOWARDS THE
TERMINALS ALLOWING WINDS TO DIMINISH...AND EVENTUALLY BACK TO THE
WEST/SOUTHWEST THURSDAY. AN AREA OF LOW PRESSURE IS PROGGED TO
MOVE FROM THE PLAINS INTO THE LOWER MISSISSIPPI VALLEY TONIGHT
RESULTING IN AN INCREASE IN MAINLY UPPER LEVEL CLOUD
COVER...THOUGH ANY PRECIP WITH THIS SYSTEM WILL STAY WELL TO OUR
WEST AND SOUTH.

BMD

&&

.MARINE...
202 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT WILL PERSIST
OVER LAKE MICHIGAN THROUGH TONIGHT AHEAD OF A RIDGE THAT STRETCHES
FROM THE NORTHWEST TERRITORIES INTO THE MISSISSIPPI VALLEY.
WINDS OF 30 KT AND FREEZING SPRAY WILL CONTINUE INTO SOME OF THE
OVERNIGHT HOURS THEN SHOULD DIMINISH EARLY THURSDAY AS THE HIGH
INCHES EAST ALLOWING THE GRADIENT TO RELAX. WINDS ALSO BACK TO THE
WEST ON THURSDAY AS THE HIGH BUILDS SOUTH OF LAKE MICHIGAN...THEN
FRESHEN UP AS LOW PRESSURE FORMS OVER ONTARIO. THIS LOW WILL BRING
A REINFORCING SHOT OF COLD AIR SOUTH ON FRIDAY BEHIND A TRAILING
COLD FRONT AND AS A STRONG ARCTIC HIGH BUILDS ACROSS CANADA INTO
THE UPPER MIDWEST. AT LEAST A SHORT WINDOW OF NORTHERLY GALES ARE
EXPECTED BEHIND THE COLD FRONT FRIDAY EVENING OR OVERNIGHT...THEN
WINDS SHOULD GRADUALLY DIMINISH OVER THE WEEKEND AS THE HIGH
BUILDS ACROSS THE GREAT LAKES.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 101732
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1132 AM CST WED FEB 10 2016

.SHORT TERM...
331 AM CST

THROUGH TONIGHT...

THE MESSAGE FOR THE REMAINDER OF THE WEEK AND THIS WEEKEND IS
SIMPLY UNSEASONABLY COLD. EARLY MORNING LOWS MAY DIP TO SUBZERO IN
OUTLYING LOCATIONS THURSDAY MORNING THEN AGAIN SATURDAY AND SUNDAY
MORNINGS. AT THIS TIME IT APPEARS FOR THE MOST PART WIND CHILLS
SHOULD REMAIN ABOVE OUR CRITERIA OF ADVISORY /WHICH IS AOB
-15F/...THOUGH COULD DIP TO THAT LEVEL LATER FRIDAY NIGHT AND
SATURDAY MORNING. NO MAJOR SNOW CHANCES EXIST THROUGH
SATURDAY...THOUGH CONTINUING TO SEE A TREND FOR PART OF NORTHWEST
INDIANA TO SEE SOME LAKE EFFECT SNOW FRIDAY NIGHT AND SATURDAY.

THE HIGHLY AMPLIFIED LONG WAVE TROUGH OVER EASTERN NORTH AMERICA
IS FINALLY SHIFTING ITS WAY EASTWARD. UPPER TROPOSPHERIC NORTHERLY
FLOW BEHIND THIS WILL KEEP THE COLD PATTERN IN PLACE THOUGH WITH A
MODIFIED ARCTIC AIR MASS HAVING SPREAD INTO THE REGION. THE MIXED
LAYER WILL WARM LITTLE TODAY WITH 925MB TEMPERATURES AROUND -16C.
THIS PROFILE AND UPSTREAM TEMPERATURES YESTERDAY LOOK TO SUPPORT
MID TEENS FOR HIGHS. THE CLOUD FORECAST FOR TODAY IS CHALLENGING
AS OFTEN CAN BE THE CASE AT THE PERIPHERY OF DEPARTING CYCLONIC
FLOW. EXPECT THAT EARLY MORNING HOLES WILL FILL IN DURING MIDDAY
WITH THE CONTINUED STEEP LAPSE RATES. DRY ADVECTION HAS BROUGHT
DEW POINTS TO AROUND OR EVEN BELOW ZERO INTO THE FORECAST
AREA...SO THE CLOUDS ARE LIKELY TO BE THIN. THESE SHOULD ADVECT
AWAY TONIGHT. COMBINED WITH WEAKENING WINDS AND A LIGHT BUT FRESH
SNOW IN PLACES...THE CLEAR NIGHT WILL SEE LOWER TO MID SINGLE
DIGITS IN MOST LOCATIONS WITH THE SUBZERO LOWS POSSIBLE IN THE
USUAL COLDER SPOTS.

MTF

&&

.LONG TERM...
331 AM CST

THURSDAY THROUGH WEDNESDAY...

HIGH PRESSURE AT THE SURFACE WILL PREVAIL THURSDAY INTO THURSDAY
NIGHT WITH THE DAYTIME HOURS OF THURSDAY LIKELY TO BE PRIMARILY
SUNNY AND ASSISTING IN A WEE BIT OF TEMPERATURE MODERATION. MODEL
GUIDANCE CONTINUES TO INDICATE A SHEARED SHORT WAVE TROUGH DIVING
SOUTHEAST FROM THE UPPER PLAINS TO THE LOWER OHIO VALLEY THURSDAY
NIGHT INTO FRIDAY. THIS IS BASICALLY RIDING THE ELEVATED
BAROCLINIC ZONE SIMILAR TO A SYSTEM TODAY OFF TO OUR SOUTHWEST.
CONTINUE TO THINK MOST SNOW WITH THIS WILL REMAIN SOUTH. FRIDAY
SHOULD BE CLOUDY THOUGH AND MAYBE ENOUGH WEAK ISENTROPIC ASCENT
FOR SOME FLURRIES.

THAT SHORT WAVE AND JET WITH REINFORCE THE COLD AIR INTO THE
REGION...BRINGING THE ARCTIC COLD FRONT BACK SOUTH FRIDAY
AFTERNOON OR EVENING. THIS SETS UP THE COLD WEEKEND PARTICULARLY
SATURDAY. WHILE AGAIN SOME FLURRIES MAY BE SEEN WITH THIS...MOST
OF THE AREA SHOULD BE DRY. THE EXCEPTION IS FAR NORTHWEST INDIANA
WHERE BOUNDARY LAYER FLOW IS LIKELY TO TURN MORE NORTHERLY WITH A
DEEP LOW FAVORED OFF THE NORTHEAST U.S. AND A 1040MB+ HIGH TO THE
WEST. FORECAST EQUILIBRIUM LEVELS FROM THE GFS ARE OVER 10000
FT...BUT MOISTURE MAY BE DRY ENOUGH THAT COVERAGE OF ANY LAKE
EFFECT SNOW SHOWERS MAY BE IN SINGLE BAND/S/. TOO EARLY YET TO
TELL IF THERE WILL BE VERY FOCUSED CONVERGENCE OR EVEN IF SNOW
SHOWERS WILL ROTATE BACK TO THE WEST FAR ENOUGH TO IMPACT PORTER
AND LAKE COUNTIES.

GLOBAL GUIDANCE HAS INDICATED A PACIFIC/CLIPPER HYBRID SYSTEM
CROSSING THE GENERAL REGION SOMETIME LATE IN THE WEEKEND/EARLY
NEXT WEEK. CONFIDENCE IN THIS SYSTEM IS LOW AND IT CERTAINLY COULD
SLOW TOO. EVEN IF THAT WERE TO HAPPEN THE COLD AIR IN ADVANCE
LOOKS LIKE THE PROFILES SHOULD BE COOL ENOUGH TO SUPPORT SNOW. HOW
MUCH IF ANY SNOW THOUGH WILL DEPEND ON ITS EXACT TRACK WHICH COULD
VARY SIGNIFICANTLY YET FOR SEVERAL MODEL RUNS.

MTF

&&

.AVIATION...
FOR THE 18Z TAFS...

FAIRLY QUIET FORECAST ON TAP FOR THE CHICAGO/ROCKFORD AREA
TERMINALS THROUGH TOMORROW. AREA OF THIN OVERCAST STRATUS THAT
WAS IN PLACE THIS MORNING HAS BECOME SCT-BKN THIS HOUR AND EXPECT
PRIMARILY VFR CONDITIONS TO PREVAIL THROUGH REMAINDER OF THE
FORECAST PERIOD. RIDGE OF HIGH PRESSURE CURRENTLY STRETCHES FROM
THE LOWER TO UPPER MISSISSIPPI VALLEY AND WILL INCH TOWARDS THE
TERMINALS ALLOWING WINDS TO DIMINISH...AND EVENTUALLY BACK TO THE
WEST/SOUTHWEST THURSDAY. AN AREA OF LOW PRESSURE IS PROGGED TO
MOVE FROM THE PLAINS INTO THE LOWER MISSISSIPPI VALLEY TONIGHT
RESULTING IN AN INCREASE IN MAINLY UPPER LEVEL CLOUD
COVER...THOUGH ANY PRECIP WITH THIS SYSTEM WILL STAY WELL TO OUR
WEST AND SOUTH.

BMD

&&

.MARINE...
309 AM CST

A FEW GALE FORCE GUSTS ARE STILL BEING REPORTED SO WILL LET THE GALE
WARNING CONTINUE. EXTENDED EACH SMALL CRAFT ADVISORY BY 6 HOURS AS
HAZARDOUS WAVES WILL LINGER LONGER THAN PREVIOUSLY FORECAST.

NORTH TO NORTHWEST WINDS TO 30 KT CONTINUE TODAY AS A WEAK LOW
SHIFTS EAST OVER NEW ENGLAND AND HIGH PRESSURE BUILDS OVER THE
NORTHERN PLAINS AND UPPER MIDWEST.  THE HIGH WEAKENS AS IT MOVES
SOUTH OF THE LAKE THURSDAY NIGHT.  WINDS WEAKEN AND BECOME WEST
THURSDAY AFTERNOON. HOWEVER...A WEAK LOW FORMS OVER EASTERN ONTARIO
THURSDAY NIGHT AND DRAGS A COLD FRONT DOWN THE LAKE FRIDAY. WINDS
BECOME NORTH TO 30 KT BEHIND THE COLD FRONT FRIDAY NIGHT.  A SMALL
CRAFT ADVISORY MAY BE NEEDED FRIDAY AFTERNOON THROUGH SATURDAY. AT
THE SAME TIME A LARGE HIGH BUILDS OVER THE PLAINS...AND REACHES THE
LAKE SATURDAY NIGHT.  WINDS WEAKEN UNDER THE HIGH AND THEN BECOME
SOUTH 15-25 KT SUNDAY AS THE HIGH MOVES OVER THE EASTERN SEABOARD.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 101154
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
554 AM CST WED FEB 10 2016

.SHORT TERM...
331 AM CST

THROUGH TONIGHT...

THE MESSAGE FOR THE REMAINDER OF THE WEEK AND THIS WEEKEND IS
SIMPLY UNSEASONABLY COLD. EARLY MORNING LOWS MAY DIP TO SUBZERO IN
OUTLYING LOCATIONS THURSDAY MORNING THEN AGAIN SATURDAY AND SUNDAY
MORNINGS. AT THIS TIME IT APPEARS FOR THE MOST PART WIND CHILLS
SHOULD REMAIN ABOVE OUR CRITERIA OF ADVISORY /WHICH IS AOB
-15F/...THOUGH COULD DIP TO THAT LEVEL LATER FRIDAY NIGHT AND
SATURDAY MORNING. NO MAJOR SNOW CHANCES EXIST THROUGH
SATURDAY...THOUGH CONTINUING TO SEE A TREND FOR PART OF NORTHWEST
INDIANA TO SEE SOME LAKE EFFECT SNOW FRIDAY NIGHT AND SATURDAY.

THE HIGHLY AMPLIFIED LONG WAVE TROUGH OVER EASTERN NORTH AMERICA
IS FINALLY SHIFTING ITS WAY EASTWARD. UPPER TROPOSPHERIC NORTHERLY
FLOW BEHIND THIS WILL KEEP THE COLD PATTERN IN PLACE THOUGH WITH A
MODIFIED ARCTIC AIR MASS HAVING SPREAD INTO THE REGION. THE MIXED
LAYER WILL WARM LITTLE TODAY WITH 925MB TEMPERATURES AROUND -16C.
THIS PROFILE AND UPSTREAM TEMPERATURES YESTERDAY LOOK TO SUPPORT
MID TEENS FOR HIGHS. THE CLOUD FORECAST FOR TODAY IS CHALLENGING
AS OFTEN CAN BE THE CASE AT THE PERIPHERY OF DEPARTING CYCLONIC
FLOW. EXPECT THAT EARLY MORNING HOLES WILL FILL IN DURING MIDDAY
WITH THE CONTINUED STEEP LAPSE RATES. DRY ADVECTION HAS BROUGHT
DEW POINTS TO AROUND OR EVEN BELOW ZERO INTO THE FORECAST
AREA...SO THE CLOUDS ARE LIKELY TO BE THIN. THESE SHOULD ADVECT
AWAY TONIGHT. COMBINED WITH WEAKENING WINDS AND A LIGHT BUT FRESH
SNOW IN PLACES...THE CLEAR NIGHT WILL SEE LOWER TO MID SINGLE
DIGITS IN MOST LOCATIONS WITH THE SUBZERO LOWS POSSIBLE IN THE
USUAL COLDER SPOTS.

MTF

&&

.LONG TERM...
331 AM CST

THURSDAY THROUGH WEDNESDAY...

HIGH PRESSURE AT THE SURFACE WILL PREVAIL THURSDAY INTO THURSDAY
NIGHT WITH THE DAYTIME HOURS OF THURSDAY LIKELY TO BE PRIMARILY
SUNNY AND ASSISTING IN A WEE BIT OF TEMPERATURE MODERATION. MODEL
GUIDANCE CONTINUES TO INDICATE A SHEARED SHORT WAVE TROUGH DIVING
SOUTHEAST FROM THE UPPER PLAINS TO THE LOWER OHIO VALLEY THURSDAY
NIGHT INTO FRIDAY. THIS IS BASICALLY RIDING THE ELEVATED
BAROCLINIC ZONE SIMILAR TO A SYSTEM TODAY OFF TO OUR SOUTHWEST.
CONTINUE TO THINK MOST SNOW WITH THIS WILL REMAIN SOUTH. FRIDAY
SHOULD BE CLOUDY THOUGH AND MAYBE ENOUGH WEAK ISENTROPIC ASCENT
FOR SOME FLURRIES.

THAT SHORT WAVE AND JET WITH REINFORCE THE COLD AIR INTO THE
REGION...BRINGING THE ARCTIC COLD FRONT BACK SOUTH FRIDAY
AFTERNOON OR EVENING. THIS SETS UP THE COLD WEEKEND PARTICULARLY
SATURDAY. WHILE AGAIN SOME FLURRIES MAY BE SEEN WITH THIS...MOST
OF THE AREA SHOULD BE DRY. THE EXCEPTION IS FAR NORTHWEST INDIANA
WHERE BOUNDARY LAYER FLOW IS LIKELY TO TURN MORE NORTHERLY WITH A
DEEP LOW FAVORED OFF THE NORTHEAST U.S. AND A 1040MB+ HIGH TO THE
WEST. FORECAST EQUILIBRIUM LEVELS FROM THE GFS ARE OVER 10000
FT...BUT MOISTURE MAY BE DRY ENOUGH THAT COVERAGE OF ANY LAKE
EFFECT SNOW SHOWERS MAY BE IN SINGLE BAND/S/. TOO EARLY YET TO
TELL IF THERE WILL BE VERY FOCUSED CONVERGENCE OR EVEN IF SNOW
SHOWERS WILL ROTATE BACK TO THE WEST FAR ENOUGH TO IMPACT PORTER
AND LAKE COUNTIES.

GLOBAL GUIDANCE HAS INDICATED A PACIFIC/CLIPPER HYBRID SYSTEM
CROSSING THE GENERAL REGION SOMETIME LATE IN THE WEEKEND/EARLY
NEXT WEEK. CONFIDENCE IN THIS SYSTEM IS LOW AND IT CERTAINLY COULD
SLOW TOO. EVEN IF THAT WERE TO HAPPEN THE COLD AIR IN ADVANCE
LOOKS LIKE THE PROFILES SHOULD BE COOL ENOUGH TO SUPPORT SNOW. HOW
MUCH IF ANY SNOW THOUGH WILL DEPEND ON ITS EXACT TRACK WHICH COULD
VARY SIGNIFICANTLY YET FOR SEVERAL MODEL RUNS.

MTF

&&

.AVIATION...
FOR THE 12Z TAFS...

A MUCH QUIETER DAY IS EXPECTED WITH NORTHWEST WINDS AT 10-15 KT
AND VFR CONDITIONS. GYY WILL LIKELY SEE GUSTS UP TO 25 KT INTO
THIS AFTN. SCT TO BKN HIGH LEVEL CLOUDS ARE MARCHING SOUTHEAST
ACROSS THE MISSISSIPPI RIVER THIS MORNING. THE CLOUDS COULD
STRUGGLE TO REACH THE EASTERN TERMINALS DUE TO THE DRY AIR MASS
OVERHEAD. THIS WOULD LEAD TO SCT VFR CIGS VS. BKN VFR CIGS. WINDS
DIMINISH TO BELOW 10 KT TONIGHT WITH CEILINGS SCATTERING OUT.

JEE

&&

.MARINE...
309 AM CST

A FEW GALE FORCE GUSTS ARE STILL BEING REPORTED SO WILL LET THE GALE
WARNING CONTINUE. EXTENDED EACH SMALL CRAFT ADVISORY BY 6 HOURS AS
HAZARDOUS WAVES WILL LINGER LONGER THAN PREVIOUSLY FORECAST.

NORTH TO NORTHWEST WINDS TO 30 KT CONTINUE TODAY AS A WEAK LOW
SHIFTS EAST OVER NEW ENGLAND AND HIGH PRESSURE BUILDS OVER THE
NORTHERN PLAINS AND UPPER MIDWEST.  THE HIGH WEAKENS AS IT MOVES
SOUTH OF THE LAKE THURSDAY NIGHT.  WINDS WEAKEN AND BECOME WEST
THURSDAY AFTERNOON. HOWEVER...A WEAK LOW FORMS OVER EASTERN ONTARIO
THURSDAY NIGHT AND DRAGS A COLD FRONT DOWN THE LAKE FRIDAY. WINDS
BECOME NORTH TO 30 KT BEHIND THE COLD FRONT FRIDAY NIGHT.  A SMALL
CRAFT ADVISORY MAY BE NEEDED FRIDAY AFTERNOON THROUGH SATURDAY. AT
THE SAME TIME A LARGE HIGH BUILDS OVER THE PLAINS...AND REACHES THE
LAKE SATURDAY NIGHT.  WINDS WEAKEN UNDER THE HIGH AND THEN BECOME
SOUTH 15-25 KT SUNDAY AS THE HIGH MOVES OVER THE EASTERN SEABOARD.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 101154
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
554 AM CST WED FEB 10 2016

.SHORT TERM...
331 AM CST

THROUGH TONIGHT...

THE MESSAGE FOR THE REMAINDER OF THE WEEK AND THIS WEEKEND IS
SIMPLY UNSEASONABLY COLD. EARLY MORNING LOWS MAY DIP TO SUBZERO IN
OUTLYING LOCATIONS THURSDAY MORNING THEN AGAIN SATURDAY AND SUNDAY
MORNINGS. AT THIS TIME IT APPEARS FOR THE MOST PART WIND CHILLS
SHOULD REMAIN ABOVE OUR CRITERIA OF ADVISORY /WHICH IS AOB
-15F/...THOUGH COULD DIP TO THAT LEVEL LATER FRIDAY NIGHT AND
SATURDAY MORNING. NO MAJOR SNOW CHANCES EXIST THROUGH
SATURDAY...THOUGH CONTINUING TO SEE A TREND FOR PART OF NORTHWEST
INDIANA TO SEE SOME LAKE EFFECT SNOW FRIDAY NIGHT AND SATURDAY.

THE HIGHLY AMPLIFIED LONG WAVE TROUGH OVER EASTERN NORTH AMERICA
IS FINALLY SHIFTING ITS WAY EASTWARD. UPPER TROPOSPHERIC NORTHERLY
FLOW BEHIND THIS WILL KEEP THE COLD PATTERN IN PLACE THOUGH WITH A
MODIFIED ARCTIC AIR MASS HAVING SPREAD INTO THE REGION. THE MIXED
LAYER WILL WARM LITTLE TODAY WITH 925MB TEMPERATURES AROUND -16C.
THIS PROFILE AND UPSTREAM TEMPERATURES YESTERDAY LOOK TO SUPPORT
MID TEENS FOR HIGHS. THE CLOUD FORECAST FOR TODAY IS CHALLENGING
AS OFTEN CAN BE THE CASE AT THE PERIPHERY OF DEPARTING CYCLONIC
FLOW. EXPECT THAT EARLY MORNING HOLES WILL FILL IN DURING MIDDAY
WITH THE CONTINUED STEEP LAPSE RATES. DRY ADVECTION HAS BROUGHT
DEW POINTS TO AROUND OR EVEN BELOW ZERO INTO THE FORECAST
AREA...SO THE CLOUDS ARE LIKELY TO BE THIN. THESE SHOULD ADVECT
AWAY TONIGHT. COMBINED WITH WEAKENING WINDS AND A LIGHT BUT FRESH
SNOW IN PLACES...THE CLEAR NIGHT WILL SEE LOWER TO MID SINGLE
DIGITS IN MOST LOCATIONS WITH THE SUBZERO LOWS POSSIBLE IN THE
USUAL COLDER SPOTS.

MTF

&&

.LONG TERM...
331 AM CST

THURSDAY THROUGH WEDNESDAY...

HIGH PRESSURE AT THE SURFACE WILL PREVAIL THURSDAY INTO THURSDAY
NIGHT WITH THE DAYTIME HOURS OF THURSDAY LIKELY TO BE PRIMARILY
SUNNY AND ASSISTING IN A WEE BIT OF TEMPERATURE MODERATION. MODEL
GUIDANCE CONTINUES TO INDICATE A SHEARED SHORT WAVE TROUGH DIVING
SOUTHEAST FROM THE UPPER PLAINS TO THE LOWER OHIO VALLEY THURSDAY
NIGHT INTO FRIDAY. THIS IS BASICALLY RIDING THE ELEVATED
BAROCLINIC ZONE SIMILAR TO A SYSTEM TODAY OFF TO OUR SOUTHWEST.
CONTINUE TO THINK MOST SNOW WITH THIS WILL REMAIN SOUTH. FRIDAY
SHOULD BE CLOUDY THOUGH AND MAYBE ENOUGH WEAK ISENTROPIC ASCENT
FOR SOME FLURRIES.

THAT SHORT WAVE AND JET WITH REINFORCE THE COLD AIR INTO THE
REGION...BRINGING THE ARCTIC COLD FRONT BACK SOUTH FRIDAY
AFTERNOON OR EVENING. THIS SETS UP THE COLD WEEKEND PARTICULARLY
SATURDAY. WHILE AGAIN SOME FLURRIES MAY BE SEEN WITH THIS...MOST
OF THE AREA SHOULD BE DRY. THE EXCEPTION IS FAR NORTHWEST INDIANA
WHERE BOUNDARY LAYER FLOW IS LIKELY TO TURN MORE NORTHERLY WITH A
DEEP LOW FAVORED OFF THE NORTHEAST U.S. AND A 1040MB+ HIGH TO THE
WEST. FORECAST EQUILIBRIUM LEVELS FROM THE GFS ARE OVER 10000
FT...BUT MOISTURE MAY BE DRY ENOUGH THAT COVERAGE OF ANY LAKE
EFFECT SNOW SHOWERS MAY BE IN SINGLE BAND/S/. TOO EARLY YET TO
TELL IF THERE WILL BE VERY FOCUSED CONVERGENCE OR EVEN IF SNOW
SHOWERS WILL ROTATE BACK TO THE WEST FAR ENOUGH TO IMPACT PORTER
AND LAKE COUNTIES.

GLOBAL GUIDANCE HAS INDICATED A PACIFIC/CLIPPER HYBRID SYSTEM
CROSSING THE GENERAL REGION SOMETIME LATE IN THE WEEKEND/EARLY
NEXT WEEK. CONFIDENCE IN THIS SYSTEM IS LOW AND IT CERTAINLY COULD
SLOW TOO. EVEN IF THAT WERE TO HAPPEN THE COLD AIR IN ADVANCE
LOOKS LIKE THE PROFILES SHOULD BE COOL ENOUGH TO SUPPORT SNOW. HOW
MUCH IF ANY SNOW THOUGH WILL DEPEND ON ITS EXACT TRACK WHICH COULD
VARY SIGNIFICANTLY YET FOR SEVERAL MODEL RUNS.

MTF

&&

.AVIATION...
FOR THE 12Z TAFS...

A MUCH QUIETER DAY IS EXPECTED WITH NORTHWEST WINDS AT 10-15 KT
AND VFR CONDITIONS. GYY WILL LIKELY SEE GUSTS UP TO 25 KT INTO
THIS AFTN. SCT TO BKN HIGH LEVEL CLOUDS ARE MARCHING SOUTHEAST
ACROSS THE MISSISSIPPI RIVER THIS MORNING. THE CLOUDS COULD
STRUGGLE TO REACH THE EASTERN TERMINALS DUE TO THE DRY AIR MASS
OVERHEAD. THIS WOULD LEAD TO SCT VFR CIGS VS. BKN VFR CIGS. WINDS
DIMINISH TO BELOW 10 KT TONIGHT WITH CEILINGS SCATTERING OUT.

JEE

&&

.MARINE...
309 AM CST

A FEW GALE FORCE GUSTS ARE STILL BEING REPORTED SO WILL LET THE GALE
WARNING CONTINUE. EXTENDED EACH SMALL CRAFT ADVISORY BY 6 HOURS AS
HAZARDOUS WAVES WILL LINGER LONGER THAN PREVIOUSLY FORECAST.

NORTH TO NORTHWEST WINDS TO 30 KT CONTINUE TODAY AS A WEAK LOW
SHIFTS EAST OVER NEW ENGLAND AND HIGH PRESSURE BUILDS OVER THE
NORTHERN PLAINS AND UPPER MIDWEST.  THE HIGH WEAKENS AS IT MOVES
SOUTH OF THE LAKE THURSDAY NIGHT.  WINDS WEAKEN AND BECOME WEST
THURSDAY AFTERNOON. HOWEVER...A WEAK LOW FORMS OVER EASTERN ONTARIO
THURSDAY NIGHT AND DRAGS A COLD FRONT DOWN THE LAKE FRIDAY. WINDS
BECOME NORTH TO 30 KT BEHIND THE COLD FRONT FRIDAY NIGHT.  A SMALL
CRAFT ADVISORY MAY BE NEEDED FRIDAY AFTERNOON THROUGH SATURDAY. AT
THE SAME TIME A LARGE HIGH BUILDS OVER THE PLAINS...AND REACHES THE
LAKE SATURDAY NIGHT.  WINDS WEAKEN UNDER THE HIGH AND THEN BECOME
SOUTH 15-25 KT SUNDAY AS THE HIGH MOVES OVER THE EASTERN SEABOARD.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 101154
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
554 AM CST WED FEB 10 2016

.SHORT TERM...
331 AM CST

THROUGH TONIGHT...

THE MESSAGE FOR THE REMAINDER OF THE WEEK AND THIS WEEKEND IS
SIMPLY UNSEASONABLY COLD. EARLY MORNING LOWS MAY DIP TO SUBZERO IN
OUTLYING LOCATIONS THURSDAY MORNING THEN AGAIN SATURDAY AND SUNDAY
MORNINGS. AT THIS TIME IT APPEARS FOR THE MOST PART WIND CHILLS
SHOULD REMAIN ABOVE OUR CRITERIA OF ADVISORY /WHICH IS AOB
-15F/...THOUGH COULD DIP TO THAT LEVEL LATER FRIDAY NIGHT AND
SATURDAY MORNING. NO MAJOR SNOW CHANCES EXIST THROUGH
SATURDAY...THOUGH CONTINUING TO SEE A TREND FOR PART OF NORTHWEST
INDIANA TO SEE SOME LAKE EFFECT SNOW FRIDAY NIGHT AND SATURDAY.

THE HIGHLY AMPLIFIED LONG WAVE TROUGH OVER EASTERN NORTH AMERICA
IS FINALLY SHIFTING ITS WAY EASTWARD. UPPER TROPOSPHERIC NORTHERLY
FLOW BEHIND THIS WILL KEEP THE COLD PATTERN IN PLACE THOUGH WITH A
MODIFIED ARCTIC AIR MASS HAVING SPREAD INTO THE REGION. THE MIXED
LAYER WILL WARM LITTLE TODAY WITH 925MB TEMPERATURES AROUND -16C.
THIS PROFILE AND UPSTREAM TEMPERATURES YESTERDAY LOOK TO SUPPORT
MID TEENS FOR HIGHS. THE CLOUD FORECAST FOR TODAY IS CHALLENGING
AS OFTEN CAN BE THE CASE AT THE PERIPHERY OF DEPARTING CYCLONIC
FLOW. EXPECT THAT EARLY MORNING HOLES WILL FILL IN DURING MIDDAY
WITH THE CONTINUED STEEP LAPSE RATES. DRY ADVECTION HAS BROUGHT
DEW POINTS TO AROUND OR EVEN BELOW ZERO INTO THE FORECAST
AREA...SO THE CLOUDS ARE LIKELY TO BE THIN. THESE SHOULD ADVECT
AWAY TONIGHT. COMBINED WITH WEAKENING WINDS AND A LIGHT BUT FRESH
SNOW IN PLACES...THE CLEAR NIGHT WILL SEE LOWER TO MID SINGLE
DIGITS IN MOST LOCATIONS WITH THE SUBZERO LOWS POSSIBLE IN THE
USUAL COLDER SPOTS.

MTF

&&

.LONG TERM...
331 AM CST

THURSDAY THROUGH WEDNESDAY...

HIGH PRESSURE AT THE SURFACE WILL PREVAIL THURSDAY INTO THURSDAY
NIGHT WITH THE DAYTIME HOURS OF THURSDAY LIKELY TO BE PRIMARILY
SUNNY AND ASSISTING IN A WEE BIT OF TEMPERATURE MODERATION. MODEL
GUIDANCE CONTINUES TO INDICATE A SHEARED SHORT WAVE TROUGH DIVING
SOUTHEAST FROM THE UPPER PLAINS TO THE LOWER OHIO VALLEY THURSDAY
NIGHT INTO FRIDAY. THIS IS BASICALLY RIDING THE ELEVATED
BAROCLINIC ZONE SIMILAR TO A SYSTEM TODAY OFF TO OUR SOUTHWEST.
CONTINUE TO THINK MOST SNOW WITH THIS WILL REMAIN SOUTH. FRIDAY
SHOULD BE CLOUDY THOUGH AND MAYBE ENOUGH WEAK ISENTROPIC ASCENT
FOR SOME FLURRIES.

THAT SHORT WAVE AND JET WITH REINFORCE THE COLD AIR INTO THE
REGION...BRINGING THE ARCTIC COLD FRONT BACK SOUTH FRIDAY
AFTERNOON OR EVENING. THIS SETS UP THE COLD WEEKEND PARTICULARLY
SATURDAY. WHILE AGAIN SOME FLURRIES MAY BE SEEN WITH THIS...MOST
OF THE AREA SHOULD BE DRY. THE EXCEPTION IS FAR NORTHWEST INDIANA
WHERE BOUNDARY LAYER FLOW IS LIKELY TO TURN MORE NORTHERLY WITH A
DEEP LOW FAVORED OFF THE NORTHEAST U.S. AND A 1040MB+ HIGH TO THE
WEST. FORECAST EQUILIBRIUM LEVELS FROM THE GFS ARE OVER 10000
FT...BUT MOISTURE MAY BE DRY ENOUGH THAT COVERAGE OF ANY LAKE
EFFECT SNOW SHOWERS MAY BE IN SINGLE BAND/S/. TOO EARLY YET TO
TELL IF THERE WILL BE VERY FOCUSED CONVERGENCE OR EVEN IF SNOW
SHOWERS WILL ROTATE BACK TO THE WEST FAR ENOUGH TO IMPACT PORTER
AND LAKE COUNTIES.

GLOBAL GUIDANCE HAS INDICATED A PACIFIC/CLIPPER HYBRID SYSTEM
CROSSING THE GENERAL REGION SOMETIME LATE IN THE WEEKEND/EARLY
NEXT WEEK. CONFIDENCE IN THIS SYSTEM IS LOW AND IT CERTAINLY COULD
SLOW TOO. EVEN IF THAT WERE TO HAPPEN THE COLD AIR IN ADVANCE
LOOKS LIKE THE PROFILES SHOULD BE COOL ENOUGH TO SUPPORT SNOW. HOW
MUCH IF ANY SNOW THOUGH WILL DEPEND ON ITS EXACT TRACK WHICH COULD
VARY SIGNIFICANTLY YET FOR SEVERAL MODEL RUNS.

MTF

&&

.AVIATION...
FOR THE 12Z TAFS...

A MUCH QUIETER DAY IS EXPECTED WITH NORTHWEST WINDS AT 10-15 KT
AND VFR CONDITIONS. GYY WILL LIKELY SEE GUSTS UP TO 25 KT INTO
THIS AFTN. SCT TO BKN HIGH LEVEL CLOUDS ARE MARCHING SOUTHEAST
ACROSS THE MISSISSIPPI RIVER THIS MORNING. THE CLOUDS COULD
STRUGGLE TO REACH THE EASTERN TERMINALS DUE TO THE DRY AIR MASS
OVERHEAD. THIS WOULD LEAD TO SCT VFR CIGS VS. BKN VFR CIGS. WINDS
DIMINISH TO BELOW 10 KT TONIGHT WITH CEILINGS SCATTERING OUT.

JEE

&&

.MARINE...
309 AM CST

A FEW GALE FORCE GUSTS ARE STILL BEING REPORTED SO WILL LET THE GALE
WARNING CONTINUE. EXTENDED EACH SMALL CRAFT ADVISORY BY 6 HOURS AS
HAZARDOUS WAVES WILL LINGER LONGER THAN PREVIOUSLY FORECAST.

NORTH TO NORTHWEST WINDS TO 30 KT CONTINUE TODAY AS A WEAK LOW
SHIFTS EAST OVER NEW ENGLAND AND HIGH PRESSURE BUILDS OVER THE
NORTHERN PLAINS AND UPPER MIDWEST.  THE HIGH WEAKENS AS IT MOVES
SOUTH OF THE LAKE THURSDAY NIGHT.  WINDS WEAKEN AND BECOME WEST
THURSDAY AFTERNOON. HOWEVER...A WEAK LOW FORMS OVER EASTERN ONTARIO
THURSDAY NIGHT AND DRAGS A COLD FRONT DOWN THE LAKE FRIDAY. WINDS
BECOME NORTH TO 30 KT BEHIND THE COLD FRONT FRIDAY NIGHT.  A SMALL
CRAFT ADVISORY MAY BE NEEDED FRIDAY AFTERNOON THROUGH SATURDAY. AT
THE SAME TIME A LARGE HIGH BUILDS OVER THE PLAINS...AND REACHES THE
LAKE SATURDAY NIGHT.  WINDS WEAKEN UNDER THE HIGH AND THEN BECOME
SOUTH 15-25 KT SUNDAY AS THE HIGH MOVES OVER THE EASTERN SEABOARD.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 100935
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
335 AM CST WED FEB 10 2016

.SHORT TERM...
331 AM CST

THROUGH TONIGHT...

THE MESSAGE FOR THE REMAINDER OF THE WEEK AND THIS WEEKEND IS
SIMPLY UNSEASONABLY COLD. EARLY MORNING LOWS MAY DIP TO SUBZERO IN
OUTLYING LOCATIONS THURSDAY MORNING THEN AGAIN SATURDAY AND SUNDAY
MORNINGS. AT THIS TIME IT APPEARS FOR THE MOST PART WIND CHILLS
SHOULD REMAIN ABOVE OUR CRITERIA OF ADVISORY /WHICH IS AOB
-15F/...THOUGH COULD DIP TO THAT LEVEL LATER FRIDAY NIGHT AND
SATURDAY MORNING. NO MAJOR SNOW CHANCES EXIST THROUGH
SATURDAY...THOUGH CONTINUING TO SEE A TREND FOR PART OF NORTHWEST
INDIANA TO SEE SOME LAKE EFFECT SNOW FRIDAY NIGHT AND SATURDAY.

THE HIGHLY AMPLIFIED LONG WAVE TROUGH OVER EASTERN NORTH AMERICA
IS FINALLY SHIFTING ITS WAY EASTWARD. UPPER TROPOSPHERIC NORTHERLY
FLOW BEHIND THIS WILL KEEP THE COLD PATTERN IN PLACE THOUGH WITH A
MODIFIED ARCTIC AIR MASS HAVING SPREAD INTO THE REGION. THE MIXED
LAYER WILL WARM LITTLE TODAY WITH 925MB TEMPERATURES AROUND -16C.
THIS PROFILE AND UPSTREAM TEMPERATURES YESTERDAY LOOK TO SUPPORT
MID TEENS FOR HIGHS. THE CLOUD FORECAST FOR TODAY IS CHALLENGING
AS OFTEN CAN BE THE CASE AT THE PERIPHERY OF DEPARTING CYCLONIC
FLOW. EXPECT THAT EARLY MORNING HOLES WILL FILL IN DURING MIDDAY
WITH THE CONTINUED STEEP LAPSE RATES. DRY ADVECTION HAS BROUGHT
DEW POINTS TO AROUND OR EVEN BELOW ZERO INTO THE FORECAST
AREA...SO THE CLOUDS ARE LIKELY TO BE THIN. THESE SHOULD ADVECT
AWAY TONIGHT. COMBINED WITH WEAKENING WINDS AND A LIGHT BUT FRESH
SNOW IN PLACES...THE CLEAR NIGHT WILL SEE LOWER TO MID SINGLE
DIGITS IN MOST LOCATIONS WITH THE SUBZERO LOWS POSSIBLE IN THE
USUAL COLDER SPOTS.

MTF

&&

.LONG TERM...
331 AM CST

THURSDAY THROUGH WEDNESDAY...

HIGH PRESSURE AT THE SURFACE WILL PREVAIL THURSDAY INTO THURSDAY
NIGHT WITH THE DAYTIME HOURS OF THURSDAY LIKELY TO BE PRIMARILY
SUNNY AND ASSISTING IN A WEE BIT OF TEMPERATURE MODERATION. MODEL
GUIDANCE CONTINUES TO INDICATE A SHEARED SHORT WAVE TROUGH DIVING
SOUTHEAST FROM THE UPPER PLAINS TO THE LOWER OHIO VALLEY THURSDAY
NIGHT INTO FRIDAY. THIS IS BASICALLY RIDING THE ELEVATED
BAROCLINIC ZONE SIMILAR TO A SYSTEM TODAY OFF TO OUR SOUTHWEST.
CONTINUE TO THINK MOST SNOW WITH THIS WILL REMAIN SOUTH. FRIDAY
SHOULD BE CLOUDY THOUGH AND MAYBE ENOUGH WEAK ISENTROPIC ASCENT
FOR SOME FLURRIES.

THAT SHORT WAVE AND JET WITH REINFORCE THE COLD AIR INTO THE
REGION...BRINGING THE ARCTIC COLD FRONT BACK SOUTH FRIDAY
AFTERNOON OR EVENING. THIS SETS UP THE COLD WEEKEND PARTICULARLY
SATURDAY. WHILE AGAIN SOME FLURRIES MAY BE SEEN WITH THIS...MOST
OF THE AREA SHOULD BE DRY. THE EXCEPTION IS FAR NORTHWEST INDIANA
WHERE BOUNDARY LAYER FLOW IS LIKELY TO TURN MORE NORTHERLY WITH A
DEEP LOW FAVORED OFF THE NORTHEAST U.S. AND A 1040MB+ HIGH TO THE
WEST. FORECAST EQUILIBRIUM LEVELS FROM THE GFS ARE OVER 10000
FT...BUT MOISTURE MAY BE DRY ENOUGH THAT COVERAGE OF ANY LAKE
EFFECT SNOW SHOWERS MAY BE IN SINGLE BAND/S/. TOO EARLY YET TO
TELL IF THERE WILL BE VERY FOCUSED CONVERGENCE OR EVEN IF SNOW
SHOWERS WILL ROTATE BACK TO THE WEST FAR ENOUGH TO IMPACT PORTER
AND LAKE COUNTIES.

GLOBAL GUIDANCE HAS INDICATED A PACIFIC/CLIPPER HYBRID SYSTEM
CROSSING THE GENERAL REGION SOMETIME LATE IN THE WEEKEND/EARLY
NEXT WEEK. CONFIDENCE IN THIS SYSTEM IS LOW AND IT CERTAINLY COULD
SLOW TOO. EVEN IF THAT WERE TO HAPPEN THE COLD AIR IN ADVANCE
LOOKS LIKE THE PROFILES SHOULD BE COOL ENOUGH TO SUPPORT SNOW. HOW
MUCH IF ANY SNOW THOUGH WILL DEPEND ON ITS EXACT TRACK WHICH COULD
VARY SIGNIFICANTLY YET FOR SEVERAL MODEL RUNS.

MTF

&&

.AVIATION...
FOR THE 06Z TAFS...

THE LOW WILL CONTINUE TO PULL AWAY AND REACH NEW ENGLAND THIS
MORNING. SNOW SHOWERS ARE ALSO PUSHING EAST. THE HEAVIER SHOWERS
ARE MAINLY EAST OF GYY BUT SCATTERED FLURRIES WILL CONTINUE AT THE
EASTERN TERMINALS THROUGH THE EARLY MORNING HOURS. GYY WILL
LIKELY BE THE ONLY LOCATION TO SEE ANY ADDITIONAL ACCUMULATING
SNOW. VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD WITH GUSTY NW
WINDS THROUGH THIS AFTERNOON. THE HIGHEST GUSTS WILL BE THROUGH
EARLY MORNING HOURS WITH MAX GUSTS TO 20 KT. NORTHWEST WINDS LESS
THAN 10 KT AND VFR CONDITIONS ARE EXPECTED TONIGHT.

JEE

&&

.MARINE...
309 AM CST

A FEW GALE FORCE GUSTS ARE STILL BEING REPORTED SO WILL LET THE GALE
WARNING CONTINUE. EXTENDED EACH SMALL CRAFT ADVISORY BY 6 HOURS AS
HAZARDOUS WAVES WILL LINGER LONGER THAN PREVIOUSLY FORECAST.

NORTH TO NORTHWEST WINDS TO 30 KT CONTINUE TODAY AS A WEAK LOW
SHIFTS EAST OVER NEW ENGLAND AND HIGH PRESSURE BUILDS OVER THE
NORTHERN PLAINS AND UPPER MIDWEST.  THE HIGH WEAKENS AS IT MOVES
SOUTH OF THE LAKE THURSDAY NIGHT.  WINDS WEAKEN AND BECOME WEST
THURSDAY AFTERNOON. HOWEVER...A WEAK LOW FORMS OVER EASTERN ONTARIO
THURSDAY NIGHT AND DRAGS A COLD FRONT DOWN THE LAKE FRIDAY. WINDS
BECOME NORTH TO 30 KT BEHIND THE COLD FRONT FRIDAY NIGHT.  A SMALL
CRAFT ADVISORY MAY BE NEEDED FRIDAY AFTERNOON THROUGH SATURDAY. AT
THE SAME TIME A LARGE HIGH BUILDS OVER THE PLAINS...AND REACHES THE
LAKE SATURDAY NIGHT.  WINDS WEAKEN UNDER THE HIGH AND THEN BECOME
SOUTH 15-25 KT SUNDAY AS THE HIGH MOVES OVER THE EASTERN SEABOARD.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 100935
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
335 AM CST WED FEB 10 2016

.SHORT TERM...
331 AM CST

THROUGH TONIGHT...

THE MESSAGE FOR THE REMAINDER OF THE WEEK AND THIS WEEKEND IS
SIMPLY UNSEASONABLY COLD. EARLY MORNING LOWS MAY DIP TO SUBZERO IN
OUTLYING LOCATIONS THURSDAY MORNING THEN AGAIN SATURDAY AND SUNDAY
MORNINGS. AT THIS TIME IT APPEARS FOR THE MOST PART WIND CHILLS
SHOULD REMAIN ABOVE OUR CRITERIA OF ADVISORY /WHICH IS AOB
-15F/...THOUGH COULD DIP TO THAT LEVEL LATER FRIDAY NIGHT AND
SATURDAY MORNING. NO MAJOR SNOW CHANCES EXIST THROUGH
SATURDAY...THOUGH CONTINUING TO SEE A TREND FOR PART OF NORTHWEST
INDIANA TO SEE SOME LAKE EFFECT SNOW FRIDAY NIGHT AND SATURDAY.

THE HIGHLY AMPLIFIED LONG WAVE TROUGH OVER EASTERN NORTH AMERICA
IS FINALLY SHIFTING ITS WAY EASTWARD. UPPER TROPOSPHERIC NORTHERLY
FLOW BEHIND THIS WILL KEEP THE COLD PATTERN IN PLACE THOUGH WITH A
MODIFIED ARCTIC AIR MASS HAVING SPREAD INTO THE REGION. THE MIXED
LAYER WILL WARM LITTLE TODAY WITH 925MB TEMPERATURES AROUND -16C.
THIS PROFILE AND UPSTREAM TEMPERATURES YESTERDAY LOOK TO SUPPORT
MID TEENS FOR HIGHS. THE CLOUD FORECAST FOR TODAY IS CHALLENGING
AS OFTEN CAN BE THE CASE AT THE PERIPHERY OF DEPARTING CYCLONIC
FLOW. EXPECT THAT EARLY MORNING HOLES WILL FILL IN DURING MIDDAY
WITH THE CONTINUED STEEP LAPSE RATES. DRY ADVECTION HAS BROUGHT
DEW POINTS TO AROUND OR EVEN BELOW ZERO INTO THE FORECAST
AREA...SO THE CLOUDS ARE LIKELY TO BE THIN. THESE SHOULD ADVECT
AWAY TONIGHT. COMBINED WITH WEAKENING WINDS AND A LIGHT BUT FRESH
SNOW IN PLACES...THE CLEAR NIGHT WILL SEE LOWER TO MID SINGLE
DIGITS IN MOST LOCATIONS WITH THE SUBZERO LOWS POSSIBLE IN THE
USUAL COLDER SPOTS.

MTF

&&

.LONG TERM...
331 AM CST

THURSDAY THROUGH WEDNESDAY...

HIGH PRESSURE AT THE SURFACE WILL PREVAIL THURSDAY INTO THURSDAY
NIGHT WITH THE DAYTIME HOURS OF THURSDAY LIKELY TO BE PRIMARILY
SUNNY AND ASSISTING IN A WEE BIT OF TEMPERATURE MODERATION. MODEL
GUIDANCE CONTINUES TO INDICATE A SHEARED SHORT WAVE TROUGH DIVING
SOUTHEAST FROM THE UPPER PLAINS TO THE LOWER OHIO VALLEY THURSDAY
NIGHT INTO FRIDAY. THIS IS BASICALLY RIDING THE ELEVATED
BAROCLINIC ZONE SIMILAR TO A SYSTEM TODAY OFF TO OUR SOUTHWEST.
CONTINUE TO THINK MOST SNOW WITH THIS WILL REMAIN SOUTH. FRIDAY
SHOULD BE CLOUDY THOUGH AND MAYBE ENOUGH WEAK ISENTROPIC ASCENT
FOR SOME FLURRIES.

THAT SHORT WAVE AND JET WITH REINFORCE THE COLD AIR INTO THE
REGION...BRINGING THE ARCTIC COLD FRONT BACK SOUTH FRIDAY
AFTERNOON OR EVENING. THIS SETS UP THE COLD WEEKEND PARTICULARLY
SATURDAY. WHILE AGAIN SOME FLURRIES MAY BE SEEN WITH THIS...MOST
OF THE AREA SHOULD BE DRY. THE EXCEPTION IS FAR NORTHWEST INDIANA
WHERE BOUNDARY LAYER FLOW IS LIKELY TO TURN MORE NORTHERLY WITH A
DEEP LOW FAVORED OFF THE NORTHEAST U.S. AND A 1040MB+ HIGH TO THE
WEST. FORECAST EQUILIBRIUM LEVELS FROM THE GFS ARE OVER 10000
FT...BUT MOISTURE MAY BE DRY ENOUGH THAT COVERAGE OF ANY LAKE
EFFECT SNOW SHOWERS MAY BE IN SINGLE BAND/S/. TOO EARLY YET TO
TELL IF THERE WILL BE VERY FOCUSED CONVERGENCE OR EVEN IF SNOW
SHOWERS WILL ROTATE BACK TO THE WEST FAR ENOUGH TO IMPACT PORTER
AND LAKE COUNTIES.

GLOBAL GUIDANCE HAS INDICATED A PACIFIC/CLIPPER HYBRID SYSTEM
CROSSING THE GENERAL REGION SOMETIME LATE IN THE WEEKEND/EARLY
NEXT WEEK. CONFIDENCE IN THIS SYSTEM IS LOW AND IT CERTAINLY COULD
SLOW TOO. EVEN IF THAT WERE TO HAPPEN THE COLD AIR IN ADVANCE
LOOKS LIKE THE PROFILES SHOULD BE COOL ENOUGH TO SUPPORT SNOW. HOW
MUCH IF ANY SNOW THOUGH WILL DEPEND ON ITS EXACT TRACK WHICH COULD
VARY SIGNIFICANTLY YET FOR SEVERAL MODEL RUNS.

MTF

&&

.AVIATION...
FOR THE 06Z TAFS...

THE LOW WILL CONTINUE TO PULL AWAY AND REACH NEW ENGLAND THIS
MORNING. SNOW SHOWERS ARE ALSO PUSHING EAST. THE HEAVIER SHOWERS
ARE MAINLY EAST OF GYY BUT SCATTERED FLURRIES WILL CONTINUE AT THE
EASTERN TERMINALS THROUGH THE EARLY MORNING HOURS. GYY WILL
LIKELY BE THE ONLY LOCATION TO SEE ANY ADDITIONAL ACCUMULATING
SNOW. VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD WITH GUSTY NW
WINDS THROUGH THIS AFTERNOON. THE HIGHEST GUSTS WILL BE THROUGH
EARLY MORNING HOURS WITH MAX GUSTS TO 20 KT. NORTHWEST WINDS LESS
THAN 10 KT AND VFR CONDITIONS ARE EXPECTED TONIGHT.

JEE

&&

.MARINE...
309 AM CST

A FEW GALE FORCE GUSTS ARE STILL BEING REPORTED SO WILL LET THE GALE
WARNING CONTINUE. EXTENDED EACH SMALL CRAFT ADVISORY BY 6 HOURS AS
HAZARDOUS WAVES WILL LINGER LONGER THAN PREVIOUSLY FORECAST.

NORTH TO NORTHWEST WINDS TO 30 KT CONTINUE TODAY AS A WEAK LOW
SHIFTS EAST OVER NEW ENGLAND AND HIGH PRESSURE BUILDS OVER THE
NORTHERN PLAINS AND UPPER MIDWEST.  THE HIGH WEAKENS AS IT MOVES
SOUTH OF THE LAKE THURSDAY NIGHT.  WINDS WEAKEN AND BECOME WEST
THURSDAY AFTERNOON. HOWEVER...A WEAK LOW FORMS OVER EASTERN ONTARIO
THURSDAY NIGHT AND DRAGS A COLD FRONT DOWN THE LAKE FRIDAY. WINDS
BECOME NORTH TO 30 KT BEHIND THE COLD FRONT FRIDAY NIGHT.  A SMALL
CRAFT ADVISORY MAY BE NEEDED FRIDAY AFTERNOON THROUGH SATURDAY. AT
THE SAME TIME A LARGE HIGH BUILDS OVER THE PLAINS...AND REACHES THE
LAKE SATURDAY NIGHT.  WINDS WEAKEN UNDER THE HIGH AND THEN BECOME
SOUTH 15-25 KT SUNDAY AS THE HIGH MOVES OVER THE EASTERN SEABOARD.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 100935
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
335 AM CST WED FEB 10 2016

.SHORT TERM...
331 AM CST

THROUGH TONIGHT...

THE MESSAGE FOR THE REMAINDER OF THE WEEK AND THIS WEEKEND IS
SIMPLY UNSEASONABLY COLD. EARLY MORNING LOWS MAY DIP TO SUBZERO IN
OUTLYING LOCATIONS THURSDAY MORNING THEN AGAIN SATURDAY AND SUNDAY
MORNINGS. AT THIS TIME IT APPEARS FOR THE MOST PART WIND CHILLS
SHOULD REMAIN ABOVE OUR CRITERIA OF ADVISORY /WHICH IS AOB
-15F/...THOUGH COULD DIP TO THAT LEVEL LATER FRIDAY NIGHT AND
SATURDAY MORNING. NO MAJOR SNOW CHANCES EXIST THROUGH
SATURDAY...THOUGH CONTINUING TO SEE A TREND FOR PART OF NORTHWEST
INDIANA TO SEE SOME LAKE EFFECT SNOW FRIDAY NIGHT AND SATURDAY.

THE HIGHLY AMPLIFIED LONG WAVE TROUGH OVER EASTERN NORTH AMERICA
IS FINALLY SHIFTING ITS WAY EASTWARD. UPPER TROPOSPHERIC NORTHERLY
FLOW BEHIND THIS WILL KEEP THE COLD PATTERN IN PLACE THOUGH WITH A
MODIFIED ARCTIC AIR MASS HAVING SPREAD INTO THE REGION. THE MIXED
LAYER WILL WARM LITTLE TODAY WITH 925MB TEMPERATURES AROUND -16C.
THIS PROFILE AND UPSTREAM TEMPERATURES YESTERDAY LOOK TO SUPPORT
MID TEENS FOR HIGHS. THE CLOUD FORECAST FOR TODAY IS CHALLENGING
AS OFTEN CAN BE THE CASE AT THE PERIPHERY OF DEPARTING CYCLONIC
FLOW. EXPECT THAT EARLY MORNING HOLES WILL FILL IN DURING MIDDAY
WITH THE CONTINUED STEEP LAPSE RATES. DRY ADVECTION HAS BROUGHT
DEW POINTS TO AROUND OR EVEN BELOW ZERO INTO THE FORECAST
AREA...SO THE CLOUDS ARE LIKELY TO BE THIN. THESE SHOULD ADVECT
AWAY TONIGHT. COMBINED WITH WEAKENING WINDS AND A LIGHT BUT FRESH
SNOW IN PLACES...THE CLEAR NIGHT WILL SEE LOWER TO MID SINGLE
DIGITS IN MOST LOCATIONS WITH THE SUBZERO LOWS POSSIBLE IN THE
USUAL COLDER SPOTS.

MTF

&&

.LONG TERM...
331 AM CST

THURSDAY THROUGH WEDNESDAY...

HIGH PRESSURE AT THE SURFACE WILL PREVAIL THURSDAY INTO THURSDAY
NIGHT WITH THE DAYTIME HOURS OF THURSDAY LIKELY TO BE PRIMARILY
SUNNY AND ASSISTING IN A WEE BIT OF TEMPERATURE MODERATION. MODEL
GUIDANCE CONTINUES TO INDICATE A SHEARED SHORT WAVE TROUGH DIVING
SOUTHEAST FROM THE UPPER PLAINS TO THE LOWER OHIO VALLEY THURSDAY
NIGHT INTO FRIDAY. THIS IS BASICALLY RIDING THE ELEVATED
BAROCLINIC ZONE SIMILAR TO A SYSTEM TODAY OFF TO OUR SOUTHWEST.
CONTINUE TO THINK MOST SNOW WITH THIS WILL REMAIN SOUTH. FRIDAY
SHOULD BE CLOUDY THOUGH AND MAYBE ENOUGH WEAK ISENTROPIC ASCENT
FOR SOME FLURRIES.

THAT SHORT WAVE AND JET WITH REINFORCE THE COLD AIR INTO THE
REGION...BRINGING THE ARCTIC COLD FRONT BACK SOUTH FRIDAY
AFTERNOON OR EVENING. THIS SETS UP THE COLD WEEKEND PARTICULARLY
SATURDAY. WHILE AGAIN SOME FLURRIES MAY BE SEEN WITH THIS...MOST
OF THE AREA SHOULD BE DRY. THE EXCEPTION IS FAR NORTHWEST INDIANA
WHERE BOUNDARY LAYER FLOW IS LIKELY TO TURN MORE NORTHERLY WITH A
DEEP LOW FAVORED OFF THE NORTHEAST U.S. AND A 1040MB+ HIGH TO THE
WEST. FORECAST EQUILIBRIUM LEVELS FROM THE GFS ARE OVER 10000
FT...BUT MOISTURE MAY BE DRY ENOUGH THAT COVERAGE OF ANY LAKE
EFFECT SNOW SHOWERS MAY BE IN SINGLE BAND/S/. TOO EARLY YET TO
TELL IF THERE WILL BE VERY FOCUSED CONVERGENCE OR EVEN IF SNOW
SHOWERS WILL ROTATE BACK TO THE WEST FAR ENOUGH TO IMPACT PORTER
AND LAKE COUNTIES.

GLOBAL GUIDANCE HAS INDICATED A PACIFIC/CLIPPER HYBRID SYSTEM
CROSSING THE GENERAL REGION SOMETIME LATE IN THE WEEKEND/EARLY
NEXT WEEK. CONFIDENCE IN THIS SYSTEM IS LOW AND IT CERTAINLY COULD
SLOW TOO. EVEN IF THAT WERE TO HAPPEN THE COLD AIR IN ADVANCE
LOOKS LIKE THE PROFILES SHOULD BE COOL ENOUGH TO SUPPORT SNOW. HOW
MUCH IF ANY SNOW THOUGH WILL DEPEND ON ITS EXACT TRACK WHICH COULD
VARY SIGNIFICANTLY YET FOR SEVERAL MODEL RUNS.

MTF

&&

.AVIATION...
FOR THE 06Z TAFS...

THE LOW WILL CONTINUE TO PULL AWAY AND REACH NEW ENGLAND THIS
MORNING. SNOW SHOWERS ARE ALSO PUSHING EAST. THE HEAVIER SHOWERS
ARE MAINLY EAST OF GYY BUT SCATTERED FLURRIES WILL CONTINUE AT THE
EASTERN TERMINALS THROUGH THE EARLY MORNING HOURS. GYY WILL
LIKELY BE THE ONLY LOCATION TO SEE ANY ADDITIONAL ACCUMULATING
SNOW. VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD WITH GUSTY NW
WINDS THROUGH THIS AFTERNOON. THE HIGHEST GUSTS WILL BE THROUGH
EARLY MORNING HOURS WITH MAX GUSTS TO 20 KT. NORTHWEST WINDS LESS
THAN 10 KT AND VFR CONDITIONS ARE EXPECTED TONIGHT.

JEE

&&

.MARINE...
309 AM CST

A FEW GALE FORCE GUSTS ARE STILL BEING REPORTED SO WILL LET THE GALE
WARNING CONTINUE. EXTENDED EACH SMALL CRAFT ADVISORY BY 6 HOURS AS
HAZARDOUS WAVES WILL LINGER LONGER THAN PREVIOUSLY FORECAST.

NORTH TO NORTHWEST WINDS TO 30 KT CONTINUE TODAY AS A WEAK LOW
SHIFTS EAST OVER NEW ENGLAND AND HIGH PRESSURE BUILDS OVER THE
NORTHERN PLAINS AND UPPER MIDWEST.  THE HIGH WEAKENS AS IT MOVES
SOUTH OF THE LAKE THURSDAY NIGHT.  WINDS WEAKEN AND BECOME WEST
THURSDAY AFTERNOON. HOWEVER...A WEAK LOW FORMS OVER EASTERN ONTARIO
THURSDAY NIGHT AND DRAGS A COLD FRONT DOWN THE LAKE FRIDAY. WINDS
BECOME NORTH TO 30 KT BEHIND THE COLD FRONT FRIDAY NIGHT.  A SMALL
CRAFT ADVISORY MAY BE NEEDED FRIDAY AFTERNOON THROUGH SATURDAY. AT
THE SAME TIME A LARGE HIGH BUILDS OVER THE PLAINS...AND REACHES THE
LAKE SATURDAY NIGHT.  WINDS WEAKEN UNDER THE HIGH AND THEN BECOME
SOUTH 15-25 KT SUNDAY AS THE HIGH MOVES OVER THE EASTERN SEABOARD.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 100909
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
309 AM CST WED FEB 10 2016

.UPDATE...
833 PM CST

LIGHT SNOW SHOWERS/FLURRIES CONTINUE TO SLIDE EAST/SOUTHEAST
ACROSS THE WESTERN GREAT LAKES ALONG THE BACK EDGE OF A DEPARTING
MID-LVL VORT MAX. WITH A SHALLOW DENDRITIC GROWTH ZONE...AND
MINIMAL MOISTURE WITHIN THE COLUMN...IT IS MORE OF A SMALL FLAKE
OR HIGH VOLUME OF ICE CRYSTALS THAT ARE CAUSING THE REDUCTION TO
VISIBILITIES DUE TO THE COLD TEMPS IN THE LOWEST FEW 0-3KM OF THE
ATMOSPHERE. FORTUNATELY THE BACK EDGE OF THE PRECIP FIELD IS
ALREADY PUSHING INTO WESTERN IL...AND WILL CONTINUE TO PROGRESS
EAST THROUGH THE REMAINDER OF THE EVENING AS ANTI-CYCLONIC FLOW
BEGINS TO BACK WINDS TO THE NORTHWEST/WEST AND SETUP A LAKE EFFECT
CONDS FOR AREAS DOWNSTREAM OF LAKE MICHIGAN AND PERHAPS NORTHWEST
IN OR MAINLY FAR NORTHEAST PORTER COUNTY.

TEMPS OVERNIGHT WILL CONTINUE TO RADIATE...MAINLY AFTER MIDNIGHT
AS DRIER AIR ARRIVES AND HELPS TO SCOUR THE THICKER CLOUD COVER.
THIS WILL ALLOW TEMPS TO DIP INTO THE SINGLE DIGITS ABOVE ZERO IN
THE WEST/SOUTHWEST AND WHERE CLOUDS LINGER LONGER TEMPS WILL BE
AROUND 10-14 DEG OVERNIGHT.

BEACHLER

&&

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

THE LOW WILL CONTINUE TO PULL AWAY AND REACH NEW ENGLAND THIS
MORNING. SNOW SHOWERS ARE ALSO PUSHING EAST. THE HEAVIER SHOWERS
ARE MAINLY EAST OF GYY BUT SCATTERED FLURRIES WILL CONTINUE AT THE
EASTERN TERMINALS THROUGH THE EARLY MORNING HOURS. GYY WILL
LIKELY BE THE ONLY LOCATION TO SEE ANY ADDITIONAL ACCUMULATING
SNOW. VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD WITH GUSTY NW
WINDS THROUGH THIS AFTERNOON. THE HIGHEST GUSTS WILL BE THROUGH
EARLY MORNING HOURS WITH MAX GUSTS TO 20 KT. NORTHWEST WINDS LESS
THAN 10 KT AND VFR CONDITIONS ARE EXPECTED TONIGHT.

JEE

&&

.MARINE...
309 AM CST

A FEW GALE FORCE GUSTS ARE STILL BEING REPORTED SO WILL LET THE GALE
WARNING CONTINUE. EXTENDED EACH SMALL CRAFT ADVISORY BY 6 HOURS AS
HAZARDOUS WAVES WILL LINGER LONGER THAN PREVIOUSLY FORECAST.

NORTH TO NORTHWEST WINDS TO 30 KT CONTINUE TODAY AS A WEAK LOW
SHIFTS EAST OVER NEW ENGLAND AND HIGH PRESSURE BUILDS OVER THE
NORTHERN PLAINS AND UPPER MIDWEST.  THE HIGH WEAKENS AS IT MOVES
SOUTH OF THE LAKE THURSDAY NIGHT.  WINDS WEAKEN AND BECOME WEST
THURSDAY AFTERNOON. HOWEVER...A WEAK LOW FORMS OVER EASTERN ONTARIO
THURSDAY NIGHT AND DRAGS A COLD FRONT DOWN THE LAKE FRIDAY. WINDS
BECOME NORTH TO 30 KT BEHIND THE COLD FRONT FRIDAY NIGHT.  A SMALL
CRAFT ADVISORY MAY BE NEEDED FRIDAY AFTERNOON THROUGH SATURDAY. AT
THE SAME TIME A LARGE HIGH BUILDS OVER THE PLAINS...AND REACHES THE
LAKE SATURDAY NIGHT.  WINDS WEAKEN UNDER THE HIGH AND THEN BECOME
SOUTH 15-25 KT SUNDAY AS THE HIGH MOVES OVER THE EASTERN SEABOARD.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 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 100546
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1146 PM CST TUE FEB 9 2016

.UPDATE...
833 PM CST

LIGHT SNOW SHOWERS/FLURRIES CONTINUE TO SLIDE EAST/SOUTHEAST
ACROSS THE WESTERN GREAT LAKES ALONG THE BACK EDGE OF A DEPARTING
MID-LVL VORT MAX. WITH A SHALLOW DENDRITIC GROWTH ZONE...AND
MINIMAL MOISTURE WITHIN THE COLUMN...IT IS MORE OF A SMALL FLAKE
OR HIGH VOLUME OF ICE CRYSTALS THAT ARE CAUSING THE REDUCTION TO
VISIBILITIES DUE TO THE COLD TEMPS IN THE LOWEST FEW 0-3KM OF THE
ATMOSPHERE. FORTUNATELY THE BACK EDGE OF THE PRECIP FIELD IS
ALREADY PUSHING INTO WESTERN IL...AND WILL CONTINUE TO PROGRESS
EAST THROUGH THE REMAINDER OF THE EVENING AS ANTI-CYCLONIC FLOW
BEGINS TO BACK WINDS TO THE NORTHWEST/WEST AND SETUP A LAKE EFFECT
CONDS FOR AREAS DOWNSTREAM OF LAKE MICHIGAN AND PERHAPS NORTHWEST
IN OR MAINLY FAR NORTHEAST PORTER COUNTY.

TEMPS OVERNIGHT WILL CONTINUE TO RADIATE...MAINLY AFTER MIDNIGHT
AS DRIER AIR ARRIVES AND HELPS TO SCOUR THE THICKER CLOUD COVER.
THIS WILL ALLOW TEMPS TO DIP INTO THE SINGLE DIGITS ABOVE ZERO IN
THE WEST/SOUTHWEST AND WHERE CLOUDS LINGER LONGER TEMPS WILL BE
AROUND 10-14 DEG OVERNIGHT.

BEACHLER

&&

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

THE LOW WILL CONTINUE TO PULL AWAY AND REACH NEW ENGLAND THIS
MORNING. SNOW SHOWERS ARE ALSO PUSHING EAST. THE HEAVIER SHOWERS
ARE MAINLY EAST OF GYY BUT SCATTERED FLURRIES WILL CONTINUE AT THE
EASTERN TERMINALS THROUGH THE EARLY MORNING HOURS. GYY WILL
LIKELY BE THE ONLY LOCATION TO SEE ANY ADDITIONAL ACCUMULATING
SNOW. VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD WITH GUSTY NW
WINDS THROUGH THIS AFTERNOON. THE HIGHEST GUSTS WILL BE THROUGH
EARLY MORNING HOURS WITH MAX GUSTS TO 20 KT. NORTHWEST WINDS LESS
THAN 10 KT AND VFR CONDITIONS ARE EXPECTED TONIGHT.

JEE

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 100546
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1146 PM CST TUE FEB 9 2016

.UPDATE...
833 PM CST

LIGHT SNOW SHOWERS/FLURRIES CONTINUE TO SLIDE EAST/SOUTHEAST
ACROSS THE WESTERN GREAT LAKES ALONG THE BACK EDGE OF A DEPARTING
MID-LVL VORT MAX. WITH A SHALLOW DENDRITIC GROWTH ZONE...AND
MINIMAL MOISTURE WITHIN THE COLUMN...IT IS MORE OF A SMALL FLAKE
OR HIGH VOLUME OF ICE CRYSTALS THAT ARE CAUSING THE REDUCTION TO
VISIBILITIES DUE TO THE COLD TEMPS IN THE LOWEST FEW 0-3KM OF THE
ATMOSPHERE. FORTUNATELY THE BACK EDGE OF THE PRECIP FIELD IS
ALREADY PUSHING INTO WESTERN IL...AND WILL CONTINUE TO PROGRESS
EAST THROUGH THE REMAINDER OF THE EVENING AS ANTI-CYCLONIC FLOW
BEGINS TO BACK WINDS TO THE NORTHWEST/WEST AND SETUP A LAKE EFFECT
CONDS FOR AREAS DOWNSTREAM OF LAKE MICHIGAN AND PERHAPS NORTHWEST
IN OR MAINLY FAR NORTHEAST PORTER COUNTY.

TEMPS OVERNIGHT WILL CONTINUE TO RADIATE...MAINLY AFTER MIDNIGHT
AS DRIER AIR ARRIVES AND HELPS TO SCOUR THE THICKER CLOUD COVER.
THIS WILL ALLOW TEMPS TO DIP INTO THE SINGLE DIGITS ABOVE ZERO IN
THE WEST/SOUTHWEST AND WHERE CLOUDS LINGER LONGER TEMPS WILL BE
AROUND 10-14 DEG OVERNIGHT.

BEACHLER

&&

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

THE LOW WILL CONTINUE TO PULL AWAY AND REACH NEW ENGLAND THIS
MORNING. SNOW SHOWERS ARE ALSO PUSHING EAST. THE HEAVIER SHOWERS
ARE MAINLY EAST OF GYY BUT SCATTERED FLURRIES WILL CONTINUE AT THE
EASTERN TERMINALS THROUGH THE EARLY MORNING HOURS. GYY WILL
LIKELY BE THE ONLY LOCATION TO SEE ANY ADDITIONAL ACCUMULATING
SNOW. VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD WITH GUSTY NW
WINDS THROUGH THIS AFTERNOON. THE HIGHEST GUSTS WILL BE THROUGH
EARLY MORNING HOURS WITH MAX GUSTS TO 20 KT. NORTHWEST WINDS LESS
THAN 10 KT AND VFR CONDITIONS ARE EXPECTED TONIGHT.

JEE

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 100546
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1146 PM CST TUE FEB 9 2016

.UPDATE...
833 PM CST

LIGHT SNOW SHOWERS/FLURRIES CONTINUE TO SLIDE EAST/SOUTHEAST
ACROSS THE WESTERN GREAT LAKES ALONG THE BACK EDGE OF A DEPARTING
MID-LVL VORT MAX. WITH A SHALLOW DENDRITIC GROWTH ZONE...AND
MINIMAL MOISTURE WITHIN THE COLUMN...IT IS MORE OF A SMALL FLAKE
OR HIGH VOLUME OF ICE CRYSTALS THAT ARE CAUSING THE REDUCTION TO
VISIBILITIES DUE TO THE COLD TEMPS IN THE LOWEST FEW 0-3KM OF THE
ATMOSPHERE. FORTUNATELY THE BACK EDGE OF THE PRECIP FIELD IS
ALREADY PUSHING INTO WESTERN IL...AND WILL CONTINUE TO PROGRESS
EAST THROUGH THE REMAINDER OF THE EVENING AS ANTI-CYCLONIC FLOW
BEGINS TO BACK WINDS TO THE NORTHWEST/WEST AND SETUP A LAKE EFFECT
CONDS FOR AREAS DOWNSTREAM OF LAKE MICHIGAN AND PERHAPS NORTHWEST
IN OR MAINLY FAR NORTHEAST PORTER COUNTY.

TEMPS OVERNIGHT WILL CONTINUE TO RADIATE...MAINLY AFTER MIDNIGHT
AS DRIER AIR ARRIVES AND HELPS TO SCOUR THE THICKER CLOUD COVER.
THIS WILL ALLOW TEMPS TO DIP INTO THE SINGLE DIGITS ABOVE ZERO IN
THE WEST/SOUTHWEST AND WHERE CLOUDS LINGER LONGER TEMPS WILL BE
AROUND 10-14 DEG OVERNIGHT.

BEACHLER

&&

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

THE LOW WILL CONTINUE TO PULL AWAY AND REACH NEW ENGLAND THIS
MORNING. SNOW SHOWERS ARE ALSO PUSHING EAST. THE HEAVIER SHOWERS
ARE MAINLY EAST OF GYY BUT SCATTERED FLURRIES WILL CONTINUE AT THE
EASTERN TERMINALS THROUGH THE EARLY MORNING HOURS. GYY WILL
LIKELY BE THE ONLY LOCATION TO SEE ANY ADDITIONAL ACCUMULATING
SNOW. VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD WITH GUSTY NW
WINDS THROUGH THIS AFTERNOON. THE HIGHEST GUSTS WILL BE THROUGH
EARLY MORNING HOURS WITH MAX GUSTS TO 20 KT. NORTHWEST WINDS LESS
THAN 10 KT AND VFR CONDITIONS ARE EXPECTED TONIGHT.

JEE

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 100457
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1057 PM CST TUE FEB 9 2016

.UPDATE...
833 PM CST

LIGHT SNOW SHOWERS/FLURRIES CONTINUE TO SLIDE EAST/SOUTHEAST
ACROSS THE WESTERN GREAT LAKES ALONG THE BACK EDGE OF A DEPARTING
MID-LVL VORT MAX. WITH A SHALLOW DENDRITIC GROWTH ZONE...AND
MINIMAL MOISTURE WITHIN THE COLUMN...IT IS MORE OF A SMALL FLAKE
OR HIGH VOLUME OF ICE CRYSTALS THAT ARE CAUSING THE REDUCTION TO
VISIBILITIES DUE TO THE COLD TEMPS IN THE LOWEST FEW 0-3KM OF THE
ATMOSPHERE. FORTUNATELY THE BACK EDGE OF THE PRECIP FIELD IS
ALREADY PUSHING INTO WESTERN IL...AND WILL CONTINUE TO PROGRESS
EAST THROUGH THE REMAINDER OF THE EVENING AS ANTI-CYCLONIC FLOW
BEGINS TO BACK WINDS TO THE NORTHWEST/WEST AND SETUP A LAKE EFFECT
CONDS FOR AREAS DOWNSTREAM OF LAKE MICHIGAN AND PERHAPS NORTHWEST
IN OR MAINLY FAR NORTHEAST PORTER COUNTY.

TEMPS OVERNIGHT WILL CONTINUE TO RADIATE...MAINLY AFTER MIDNIGHT
AS DRIER AIR ARRIVES AND HELPS TO SCOUR THE THICKER CLOUD COVER.
THIS WILL ALLOW TEMPS TO DIP INTO THE SINGLE DIGITS ABOVE ZERO IN
THE WEST/SOUTHWEST AND WHERE CLOUDS LINGER LONGER TEMPS WILL BE
AROUND 10-14 DEG OVERNIGHT.

BEACHLER

&&

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

THE BULK OF THE STEADIER SNOW SHOWERS ARE EXITING TO THE
EAST/SOUTHEAT OF THE TERMINALS AT THIS TIME...BUT PATTERN WOULD
SUPPORT AT LEAST SOME FLURRIES TO CONTINUE ACROSS MUCH OF THE AREA
EARLY THIS MORNING. THIS IS CONSISTENT LOOKING UPSTREAM WITH
ADDITIONAL LIGHT PRECIP STILL DROPPING SOUTHEAST THROUGH THE
REGION. SO HAVE MAINTAINED A VCSH IN THE TAFS FOR THE REMAINDER OF
THE MORNING TO REFLECT LATEST THINKING. VFR CEILINGS SHOULD
PREVAIL AND ALTHOUGH THERE SOME HOLES IN THIS CLOUD COVER
DEVELOPING...UPSTREAM CEILINGS WILL LIKELY CONTINUE TO DROP
TOWARDS THE TERMINALS. VFR CONDTIONS STILL EXPECTED LATER TODAY
INTO TONIGHT WHILE NORTHWEST WINDS DIMINISH THROUGH THE PERIOD.

RODRIGUEZ

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 100457
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1057 PM CST TUE FEB 9 2016

.UPDATE...
833 PM CST

LIGHT SNOW SHOWERS/FLURRIES CONTINUE TO SLIDE EAST/SOUTHEAST
ACROSS THE WESTERN GREAT LAKES ALONG THE BACK EDGE OF A DEPARTING
MID-LVL VORT MAX. WITH A SHALLOW DENDRITIC GROWTH ZONE...AND
MINIMAL MOISTURE WITHIN THE COLUMN...IT IS MORE OF A SMALL FLAKE
OR HIGH VOLUME OF ICE CRYSTALS THAT ARE CAUSING THE REDUCTION TO
VISIBILITIES DUE TO THE COLD TEMPS IN THE LOWEST FEW 0-3KM OF THE
ATMOSPHERE. FORTUNATELY THE BACK EDGE OF THE PRECIP FIELD IS
ALREADY PUSHING INTO WESTERN IL...AND WILL CONTINUE TO PROGRESS
EAST THROUGH THE REMAINDER OF THE EVENING AS ANTI-CYCLONIC FLOW
BEGINS TO BACK WINDS TO THE NORTHWEST/WEST AND SETUP A LAKE EFFECT
CONDS FOR AREAS DOWNSTREAM OF LAKE MICHIGAN AND PERHAPS NORTHWEST
IN OR MAINLY FAR NORTHEAST PORTER COUNTY.

TEMPS OVERNIGHT WILL CONTINUE TO RADIATE...MAINLY AFTER MIDNIGHT
AS DRIER AIR ARRIVES AND HELPS TO SCOUR THE THICKER CLOUD COVER.
THIS WILL ALLOW TEMPS TO DIP INTO THE SINGLE DIGITS ABOVE ZERO IN
THE WEST/SOUTHWEST AND WHERE CLOUDS LINGER LONGER TEMPS WILL BE
AROUND 10-14 DEG OVERNIGHT.

BEACHLER

&&

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

THE BULK OF THE STEADIER SNOW SHOWERS ARE EXITING TO THE
EAST/SOUTHEAT OF THE TERMINALS AT THIS TIME...BUT PATTERN WOULD
SUPPORT AT LEAST SOME FLURRIES TO CONTINUE ACROSS MUCH OF THE AREA
EARLY THIS MORNING. THIS IS CONSISTENT LOOKING UPSTREAM WITH
ADDITIONAL LIGHT PRECIP STILL DROPPING SOUTHEAST THROUGH THE
REGION. SO HAVE MAINTAINED A VCSH IN THE TAFS FOR THE REMAINDER OF
THE MORNING TO REFLECT LATEST THINKING. VFR CEILINGS SHOULD
PREVAIL AND ALTHOUGH THERE SOME HOLES IN THIS CLOUD COVER
DEVELOPING...UPSTREAM CEILINGS WILL LIKELY CONTINUE TO DROP
TOWARDS THE TERMINALS. VFR CONDTIONS STILL EXPECTED LATER TODAY
INTO TONIGHT WHILE NORTHWEST WINDS DIMINISH THROUGH THE PERIOD.

RODRIGUEZ

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 100457
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1057 PM CST TUE FEB 9 2016

.UPDATE...
833 PM CST

LIGHT SNOW SHOWERS/FLURRIES CONTINUE TO SLIDE EAST/SOUTHEAST
ACROSS THE WESTERN GREAT LAKES ALONG THE BACK EDGE OF A DEPARTING
MID-LVL VORT MAX. WITH A SHALLOW DENDRITIC GROWTH ZONE...AND
MINIMAL MOISTURE WITHIN THE COLUMN...IT IS MORE OF A SMALL FLAKE
OR HIGH VOLUME OF ICE CRYSTALS THAT ARE CAUSING THE REDUCTION TO
VISIBILITIES DUE TO THE COLD TEMPS IN THE LOWEST FEW 0-3KM OF THE
ATMOSPHERE. FORTUNATELY THE BACK EDGE OF THE PRECIP FIELD IS
ALREADY PUSHING INTO WESTERN IL...AND WILL CONTINUE TO PROGRESS
EAST THROUGH THE REMAINDER OF THE EVENING AS ANTI-CYCLONIC FLOW
BEGINS TO BACK WINDS TO THE NORTHWEST/WEST AND SETUP A LAKE EFFECT
CONDS FOR AREAS DOWNSTREAM OF LAKE MICHIGAN AND PERHAPS NORTHWEST
IN OR MAINLY FAR NORTHEAST PORTER COUNTY.

TEMPS OVERNIGHT WILL CONTINUE TO RADIATE...MAINLY AFTER MIDNIGHT
AS DRIER AIR ARRIVES AND HELPS TO SCOUR THE THICKER CLOUD COVER.
THIS WILL ALLOW TEMPS TO DIP INTO THE SINGLE DIGITS ABOVE ZERO IN
THE WEST/SOUTHWEST AND WHERE CLOUDS LINGER LONGER TEMPS WILL BE
AROUND 10-14 DEG OVERNIGHT.

BEACHLER

&&

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

THE BULK OF THE STEADIER SNOW SHOWERS ARE EXITING TO THE
EAST/SOUTHEAT OF THE TERMINALS AT THIS TIME...BUT PATTERN WOULD
SUPPORT AT LEAST SOME FLURRIES TO CONTINUE ACROSS MUCH OF THE AREA
EARLY THIS MORNING. THIS IS CONSISTENT LOOKING UPSTREAM WITH
ADDITIONAL LIGHT PRECIP STILL DROPPING SOUTHEAST THROUGH THE
REGION. SO HAVE MAINTAINED A VCSH IN THE TAFS FOR THE REMAINDER OF
THE MORNING TO REFLECT LATEST THINKING. VFR CEILINGS SHOULD
PREVAIL AND ALTHOUGH THERE SOME HOLES IN THIS CLOUD COVER
DEVELOPING...UPSTREAM CEILINGS WILL LIKELY CONTINUE TO DROP
TOWARDS THE TERMINALS. VFR CONDTIONS STILL EXPECTED LATER TODAY
INTO TONIGHT WHILE NORTHWEST WINDS DIMINISH THROUGH THE PERIOD.

RODRIGUEZ

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 100243
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
843 PM CST TUE FEB 9 2016

.UPDATE...
833 PM CST

LIGHT SNOW SHOWERS/FLURRIES CONTINUE TO SLIDE EAST/SOUTHEAST
ACROSS THE WESTERN GREAT LAKES ALONG THE BACK EDGE OF A DEPARTING
MID-LVL VORT MAX. WITH A SHALLOW DENDRITIC GROWTH ZONE...AND
MINIMAL MOISTURE WITHIN THE COLUMN...IT IS MORE OF A SMALL FLAKE
OR HIGH VOLUME OF ICE CRYSTALS THAT ARE CAUSING THE REDUCTION TO
VISIBILITIES DUE TO THE COLD TEMPS IN THE LOWEST FEW 0-3KM OF THE
ATMOSPHERE. FORTUNATELY THE BACK EDGE OF THE PRECIP FIELD IS
ALREADY PUSHING INTO WESTERN IL...AND WILL CONTINUE TO PROGRESS
EAST THROUGH THE REMAINDER OF THE EVENING AS ANTI-CYCLONIC FLOW
BEGINS TO BACK WINDS TO THE NORTHWEST/WEST AND SETUP A LAKE EFFECT
CONDS FOR AREAS DOWNSTREAM OF LAKE MICHIGAN AND PERHAPS NORTHWEST
IN OR MAINLY FAR NORTHEAST PORTER COUNTY.

TEMPS OVERNIGHT WILL CONTINUE TO RADIATE...MAINLY AFTER MIDNIGHT
AS DRIER AIR ARRIVES AND HELPS TO SCOUR THE THICKER CLOUD COVER.
THIS WILL ALLOW TEMPS TO DIP INTO THE SINGLE DIGITS ABOVE ZERO IN
THE WEST/SOUTHWEST AND WHERE CLOUDS LINGER LONGER TEMPS WILL BE
AROUND 10-14 DEG OVERNIGHT.

BEACHLER

&&

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 00Z TAFS...

MAIN FORECAST CONCERNS ARE WITH PERIODIC SNOW SHOWERS WITH MVFR
VIS THIS EVENING...AND PERSISTENT NORTHWEST WINDS/GUSTS.

RADAR IMAGERY SHOWING SNOW SHOWERS PERSISTING ACROSS MUCH OF THE
REGION AT THIS TIME...WITH THIS SNOW STILL EXPECTED TO IMPACT THE
TERMINALS. HOWEVER...SNOW AND LOWEST VIS OF 3-5SM SHOULD BE
PERIODIC THIS EVENING BEFORE THE SNOW EXITS CLOSER TO THE MIDNIGHT
TIME FRAME. ANY ADDITIONAL SNOW THIS EVENING SHOULD BE LIGHT
AMOUNTS...AROUND A COUPLE OF TENTHS AT MOST. VFR CEILINGS IN
PLACE WILL CONTINUE TONIGHT BEFORE SCATTERING OUT WEDNESDAY.
NORTHWEST WINDS WILL CONTINUE THROUGH THE PERIOD BUT AM EXPECTING
SLIGHTLY LOWER SPEEDS TONIGHT. WIND SPEEDS WILL FURTHER DIMINISH
WEDESDAY INTO WEDNESDAY EVENING.

RODRIGUEZ

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 100014
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
614 PM CST TUE FEB 9 2016

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 00Z TAFS...

MAIN FORECAST CONCERNS ARE WITH PERIODIC SNOW SHOWERS WITH MVFR
VIS THIS EVENING...AND PERSISTENT NORTHWEST WINDS/GUSTS.

RADAR IMAGERY SHOWING SNOW SHOWERS PERSISTING ACROSS MUCH OF THE
REGION AT THIS TIME...WITH THIS SNOW STILL EXPECTED TO IMPACT THE
TERMINALS. HOWEVER...SNOW AND LOWEST VIS OF 3-5SM SHOULD BE
PERIODIC THIS EVENING BEFORE THE SNOW EXITS CLOSER TO THE MIDNIGHT
TIME FRAME. ANY ADDITIONAL SNOW THIS EVENING SHOULD BE LIGHT
AMOUNTS...AROUND A COUPLE OF TENTHS AT MOST. VFR CEILINGS IN
PLACE WILL CONTINUE TONIGHT BEFORE SCATTERING OUT WEDNESDAY.
NORTHWEST WINDS WILL CONTINUE THROUGH THE PERIOD BUT AM EXPECTING
SLIGHTLY LOWER SPEEDS TONIGHT. WIND SPEEDS WILL FURTHER DIMINISH
WEDESDAY INTO WEDNESDAY EVENING.

RODRIGUEZ

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 100014
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
614 PM CST TUE FEB 9 2016

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 00Z TAFS...

MAIN FORECAST CONCERNS ARE WITH PERIODIC SNOW SHOWERS WITH MVFR
VIS THIS EVENING...AND PERSISTENT NORTHWEST WINDS/GUSTS.

RADAR IMAGERY SHOWING SNOW SHOWERS PERSISTING ACROSS MUCH OF THE
REGION AT THIS TIME...WITH THIS SNOW STILL EXPECTED TO IMPACT THE
TERMINALS. HOWEVER...SNOW AND LOWEST VIS OF 3-5SM SHOULD BE
PERIODIC THIS EVENING BEFORE THE SNOW EXITS CLOSER TO THE MIDNIGHT
TIME FRAME. ANY ADDITIONAL SNOW THIS EVENING SHOULD BE LIGHT
AMOUNTS...AROUND A COUPLE OF TENTHS AT MOST. VFR CEILINGS IN
PLACE WILL CONTINUE TONIGHT BEFORE SCATTERING OUT WEDNESDAY.
NORTHWEST WINDS WILL CONTINUE THROUGH THE PERIOD BUT AM EXPECTING
SLIGHTLY LOWER SPEEDS TONIGHT. WIND SPEEDS WILL FURTHER DIMINISH
WEDESDAY INTO WEDNESDAY EVENING.

RODRIGUEZ

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 100014
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
614 PM CST TUE FEB 9 2016

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 00Z TAFS...

MAIN FORECAST CONCERNS ARE WITH PERIODIC SNOW SHOWERS WITH MVFR
VIS THIS EVENING...AND PERSISTENT NORTHWEST WINDS/GUSTS.

RADAR IMAGERY SHOWING SNOW SHOWERS PERSISTING ACROSS MUCH OF THE
REGION AT THIS TIME...WITH THIS SNOW STILL EXPECTED TO IMPACT THE
TERMINALS. HOWEVER...SNOW AND LOWEST VIS OF 3-5SM SHOULD BE
PERIODIC THIS EVENING BEFORE THE SNOW EXITS CLOSER TO THE MIDNIGHT
TIME FRAME. ANY ADDITIONAL SNOW THIS EVENING SHOULD BE LIGHT
AMOUNTS...AROUND A COUPLE OF TENTHS AT MOST. VFR CEILINGS IN
PLACE WILL CONTINUE TONIGHT BEFORE SCATTERING OUT WEDNESDAY.
NORTHWEST WINDS WILL CONTINUE THROUGH THE PERIOD BUT AM EXPECTING
SLIGHTLY LOWER SPEEDS TONIGHT. WIND SPEEDS WILL FURTHER DIMINISH
WEDESDAY INTO WEDNESDAY EVENING.

RODRIGUEZ

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 092057
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
257 PM CST TUE FEB 9 2016

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 18Z TAFS...

EXPECT LIGHT SNOW SHOWERS/FLURRIES TO CONTINUE OFF AND ON THROUGH
THE REMAINDER OF THE AFTERNOON THOUGH AT LEAST FOR THE NEXT FEW
HOURS EXPECT VARIABLE HIGH END MVFR TO VFR CONDITIONS WITH LOWER
CHANCES FOR IFR. RAP/HRRR MODELS CONTINUE TO HINT AT AN UPTICK IN
ACTIVITY THIS EVENING SO ADJUSTED TIMING OF THE TEMPO TO FIT THE
BEST WINDOW OF IFR OR NEAR IFR CONDITIONS. FORECAST SOUNDINGS SHOW
A DEEP SATURATED LAYER WITHIN THE SNOW GROWTH ZONE MEANING THE
ATMOSPHERE WILL BE PRIMED TO PRODUCE DECENT SIZED DENDRITES...
HOWEVER THERE IS NO SIGNIFICANT SOURCE OF FORCING. THAT
SAID...PROBABLY WONT TAKE MUCH TO SQUEEZE OUT SOME SNOW THIS
EVENING AND AN UPPER LEVEL DISTURBANCE IS PROGGED TO DROP INTO THE
NORTHERN GREAT LAKES REGION THIS EVENING WITH MODEST MID LEVEL
HEIGHT FALLS AS FAR SOUTH AS CHICAGOLAND. KEYING IN ON THIS TO
TIME THE POSSIBILITY FOR CONDITIONS TO LOWER AGAIN...HOWEVER
CONFIDENCE IN THE DETAILS REMAINS LOW AT THIS TIME GIVEN THE VERY
BENIGN FORCING. WINDS ARE EXPECTED TO REMAIN OUT OF THE NORTHWEST
THROUGH THE PERIOD WITH GUSTS TO AROUND 20 KT MUCH OF THE TIME.

BMD

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 092057
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
257 PM CST TUE FEB 9 2016

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 18Z TAFS...

EXPECT LIGHT SNOW SHOWERS/FLURRIES TO CONTINUE OFF AND ON THROUGH
THE REMAINDER OF THE AFTERNOON THOUGH AT LEAST FOR THE NEXT FEW
HOURS EXPECT VARIABLE HIGH END MVFR TO VFR CONDITIONS WITH LOWER
CHANCES FOR IFR. RAP/HRRR MODELS CONTINUE TO HINT AT AN UPTICK IN
ACTIVITY THIS EVENING SO ADJUSTED TIMING OF THE TEMPO TO FIT THE
BEST WINDOW OF IFR OR NEAR IFR CONDITIONS. FORECAST SOUNDINGS SHOW
A DEEP SATURATED LAYER WITHIN THE SNOW GROWTH ZONE MEANING THE
ATMOSPHERE WILL BE PRIMED TO PRODUCE DECENT SIZED DENDRITES...
HOWEVER THERE IS NO SIGNIFICANT SOURCE OF FORCING. THAT
SAID...PROBABLY WONT TAKE MUCH TO SQUEEZE OUT SOME SNOW THIS
EVENING AND AN UPPER LEVEL DISTURBANCE IS PROGGED TO DROP INTO THE
NORTHERN GREAT LAKES REGION THIS EVENING WITH MODEST MID LEVEL
HEIGHT FALLS AS FAR SOUTH AS CHICAGOLAND. KEYING IN ON THIS TO
TIME THE POSSIBILITY FOR CONDITIONS TO LOWER AGAIN...HOWEVER
CONFIDENCE IN THE DETAILS REMAINS LOW AT THIS TIME GIVEN THE VERY
BENIGN FORCING. WINDS ARE EXPECTED TO REMAIN OUT OF THE NORTHWEST
THROUGH THE PERIOD WITH GUSTS TO AROUND 20 KT MUCH OF THE TIME.

BMD

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 092057
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
257 PM CST TUE FEB 9 2016

.SHORT TERM...
254 PM CST

TONIGHT THROUGH WEDNESDAY NIGHT...

SHORT TERM FORECAST CONCERNS CONTINUE TO BE DETAILS OF SNOW
SHOWER COVERAGE/TIMING AND LIGHT SNOWFALL ACCUMULATIONS...AND
HEAVIER LAKE-EFFECT SNOW SHOWERS FOR NORTHWEST INDIANA AND
PRIMARILY PORTER COUNTY. SECONDARY FOCUS IS ON COLD TEMPERATURES
THROUGH THE PERIOD AND SUB-ZERO WIND CHILLS DURING THE OVERNIGHT
AND EARLY MORNING HOURS.

HIGH AMPLITUDE UPPER TROUGH REMAINS ACROSS THE EASTERN HALF OF
NORTH AMERICA THIS AFTERNOON...WITH A CLOSED LOW CENTERED OVER THE
EASTERN GREAT LAKES AND UPPER OHIO VALLEY REGION. NORTH-NORTHWEST
FLOW WAS ACROSS THE UPPER MIDWEST AND WESTERN GREAT LAKES TO THE
WEST OF THE LARGE SCALE TROUGH AXIS. A SERIES OF SHEARED SMALLER
SCALE MID-LEVEL SHORT WAVE DISTURBANCES MOVING THROUGH THE FLOW
CONTINUE TO BE THE FOCUSING MECHANISMS FOR MODULATING AREAS/TIMING
OF MORE CONCENTRATED LIGHT SNOW AND CONVECTIVE SNOW SHOWERS...WITH
COLD ARCTIC AIR OTHERWISE SUPPORTING OCCASIONAL FLURRIES OR VERY
LIGHT SNOW SHOWERS ACROSS THE REGION.

12Z UPPER AIR ANALYSIS...AFTERNOON WATER VAPOR AND CURRENT RAP
INITIALIZATIONS DEPICT STRONGER SHORT WAVE ENERGY MOVING SOUTHEAST
OF THE CWA ACROSS THE OHIO VALLEY. WEAKER/SHEARED MID-LEVEL
VORTICITY AXIS TRAILS ACROSS NORTHWEST IN/NORTHEAST IL AND THE
WESTERN LAKE MICHIGAN OF WI...PROVIDING WEAK BUT PERSISTENT
FORCING ABOVE NEARLY SATURATED LOW LEVELS BELOW ABOUT 700 MB.
THERMODYNAMIC PROFILE IN THIS LAYER IS NEARLY ISOTHERMAL WITHIN
THE -12 TO -18C RANGE WHICH IS OPTIMAL FOR PRODUCING
DENDRITES...THUS NOT MUCH ASCENT NEEDED TO SQUEEZE OUT
FLURRIES/LIGHT SNOW SNOW SHOWERS ABOVE UNSTABLE BOUNDARY LAYER
WITH STEEP SFC-850 MB LAPSE RATES. CURRENT ACTIVITY APPEARS FAIRLY
LIGHT PER REGIONAL RADAR MOSAIC WITH RETURNS GENERALLY 25 DBZ OR
LESS...THOUGH GUIDANCE IS IN GENERAL AGREEMENT THAT THERE WILL BE
SOME INCREASE IN COVERAGE/INTENSITY BY EARLY THIS EVENING MAINLY
OVER NORTHEAST IL/LAKE MI/NORTHWEST INDIANA AS A MORE ROBUST SHORT
WAVE PROPAGATES SOUTHEAST FROM THE UPPER MISSISSIPPI VALLEY. HIGH-
RES RAP/HRRR-EXP GUIDANCE SUGGESTS THESE MORE ORGANIZED SNOW
SHOWERS WILL PRIMARILY AFFECT NORTHEAST IL THROUGH THE EVENING
HOURS BEFORE DIMINISHING FROM THE NORTHWEST PRE-DAWN WEDNESDAY
MORNING AS THE MID-LEVEL VORT AXIS SHIFTS EAST OF THE FORECAST
AREA. MODEL QPF IS FAIRLY LOW...ONLY A FEW HUNDREDTHS OF AN
INCH...SO WIDESPREAD ACCUMULATIONS OF MORE THAN A FEW TENTHS IS
NOT EXPECTED...THOUGH WITH THE SHOWERY NATURE OF THE MORE
CONVECTIVE ELEMENTS A FEW PLACES IN FAR NORTHEAST IL COULD PICK UP
AN INCH OR SO OF NEW SNOW. ONLY A FEW FLURRIES ARE LIKELY DURING
THE DAY WEDNESDAY WITH LOW LEVEL LAPSE RATES STILL STEEP AND
THERMAL PROFILES IN THE SNOW-GROWTH RANGE... THOUGH NO SIGNIFICANT
LARGE SCALE ASCENT.

AS FOR LAKE-EFFECT SNOW OVER NORTHWEST INDIANA...CURRENT RAP
SOUNDINGS INDICATE LAKE SURFACE TO 850 MB DELTA-T AROUND 18 C/KM
WITH EQUILIBRIUM LEVELS 5000-5500 FT...WITH SLIGHT WESTERLY
COMPONENT TO BOUNDARY LAYER WIND FIELD PRODUCING MULTI-BAND SET-UP
WITH THE STRONGEST CONVERGENT FOCUS EAST OF PORTER COUNTY ALONG
THE MICHIGAN SHORE. RAP/NAM SOUNDINGS INDICATE THAT EQUILIBRIUM
LEVELS WILL RISE THIS EVENING HOWEVER WITH DELTA-T EVENTUALLY
AROUND OR SLIGHTLY BETTER THAN 20 C/KM. BOUNDARY LAYER
CONVERGENCE...WHILE MAINTAINING A FOCUS JUST EAST OF PORTER COUNTY
DOES STRENGTHEN OVERNIGHT INTO EARLY WEDNESDAY. THUS LAKE-EFFECT
SNOW SHOWERS ARE EXPECTED TO STRENGTHEN ACROSS
NORTHERN/NORTHEASTERN PORTER COUNTY DURING THE PERIOD WITH LIGHT
ACCUMULATIONS OF POTENTIALLY A FEW INCHES LIKELY ESPECIALLY EAST
OF THE PORTER/CHESTERTON AREAS. CONVERGENCE WEAKENS DURING THE DAY
WEDNESDAY LIKELY ALLOWING FOR A DECREASE IN INTENSITY...THOUGH
SOME POTENTIAL FOR LIGHT LAKE-EFFECT SNOW SHOWERS LOOKS TO
CONTINUE INTO THURSDAY BEFORE LOW LEVEL WINDS BACK MORE WESTERLY
AND SHIFT ANY LINGERING SNOW SHOWERS EAST OF THE AREA.

COLD NORTHWEST LOW LEVEL WINDS WILL MAINTAIN ARCTIC AIR ACROSS
THE AREA THROUGH THE NEAR TERM PERIOD...WITH OVERNIGHT LOWS IN THE
SINGLE DIGITS TO AROUND 10 ABOVE IN WARMER SPOTS AND DAYTIME HIGHS
GENERALLY IN THE TEENS TO NEAR 20.

RATZER

&&

.LONG TERM...
254 PM CST

THURSDAY THROUGH TUESDAY...

THE LARGE SCALE UPPER PATTERN CONTINUES TO FEATURE A DEEP LONG-
WAVE TROUGH ACROSS EASTERN NORTH AMERICA THROUGH THE END OF THE
WEEK... REINFORCED AS ANOTHER CLOSED UPPER LOW DROPS SOUTHWARD
FROM HUDSON BAY TO SOUTHERN QUEBEC AND UPPER NEW ENGLAND BY
SATURDAY. AMPLIFIED RIDGING UPSTREAM ACROSS THE WESTERN CONUS
FLATTENS WITH TIME HOWEVER AS AN UPPER TROUGH PROPAGATES ACROSS
THE PACIFIC NORTHWEST AND THE INTERMOUNTAIN WEST. THIS EVENTUALLY
BRINGS SOME RELIEF FROM NORTHWEST FLOW FOR THE MIDWEST BY
SUNDAY...AS THE EASTERN TROUGH FINALLY DRIFTS OFF TO THE EAST AND
WEAK/FLAT UPPER RIDGE DEVELOPS DOWNSTREAM FROM THE APPROACHING
WESTERN TROUGH. CHILLY ARCTIC AIR REMAINS IN PLACE THROUGH EARLY
SUNDAY HOWEVER...BEFORE MODERATING BACK TO/SLIGHTLY ABOVE NORMAL
BY MONDAY/TUESDAY OF NEXT WEEK.

A QUICK-MOVING CLIPPER TYPE SYSTEM WILL RIDE ALONG THE BAROCLINIC
ZONE SOUTH OF THE CWA FRIDAY...AND HAVE INDICATED LOW CHANCE POPS
FOR LIGHT SNOW DURING THE DAY. CHANCES OF LIGHT LAKE-EFFECT SNOW
SHOWERS RETURN TO NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY AS
SURFACE HIGH APPROACHES AND SURFACE WINDS VEER MORE NORTHERLY FOR
A TIME...THOUGH THE REMAINDER OF THE CWA LOOKS TO BE DRY UNTIL
FLOW BECOMES SOUTH ON THE BACK SIDE OF THE HIGH WITH THE APPROACH
OF THE TROUGH FROM THE WEST WITH A CHANCE OF LIGHT SNOW LOOKS TO
BE LATE SUNDAY-MONDAY. FASTER WEST- NORTHWEST FLOW LOOKS TO
PERSIST INTO TUESDAY...WITH SOME EVIDENCE OF A QUICK CLIPPER-LIKE
SYSTEM ALSO PRESENTING SOME CHANCE OF LIGHT SNOW ON TUESDAY.

RATZER

&&

.AVIATION...
FOR THE 18Z TAFS...

EXPECT LIGHT SNOW SHOWERS/FLURRIES TO CONTINUE OFF AND ON THROUGH
THE REMAINDER OF THE AFTERNOON THOUGH AT LEAST FOR THE NEXT FEW
HOURS EXPECT VARIABLE HIGH END MVFR TO VFR CONDITIONS WITH LOWER
CHANCES FOR IFR. RAP/HRRR MODELS CONTINUE TO HINT AT AN UPTICK IN
ACTIVITY THIS EVENING SO ADJUSTED TIMING OF THE TEMPO TO FIT THE
BEST WINDOW OF IFR OR NEAR IFR CONDITIONS. FORECAST SOUNDINGS SHOW
A DEEP SATURATED LAYER WITHIN THE SNOW GROWTH ZONE MEANING THE
ATMOSPHERE WILL BE PRIMED TO PRODUCE DECENT SIZED DENDRITES...
HOWEVER THERE IS NO SIGNIFICANT SOURCE OF FORCING. THAT
SAID...PROBABLY WONT TAKE MUCH TO SQUEEZE OUT SOME SNOW THIS
EVENING AND AN UPPER LEVEL DISTURBANCE IS PROGGED TO DROP INTO THE
NORTHERN GREAT LAKES REGION THIS EVENING WITH MODEST MID LEVEL
HEIGHT FALLS AS FAR SOUTH AS CHICAGOLAND. KEYING IN ON THIS TO
TIME THE POSSIBILITY FOR CONDITIONS TO LOWER AGAIN...HOWEVER
CONFIDENCE IN THE DETAILS REMAINS LOW AT THIS TIME GIVEN THE VERY
BENIGN FORCING. WINDS ARE EXPECTED TO REMAIN OUT OF THE NORTHWEST
THROUGH THE PERIOD WITH GUSTS TO AROUND 20 KT MUCH OF THE TIME.

BMD

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 092020
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
220 PM CST TUE FEB 9 2016

.SHORT TERM...
334 AM CST

THROUGH THURSDAY...

THE FORECAST THEME OF LIGHT SNOW WITH OCCASIONAL MODERATE SNOW
SHOWERS REMAINS ON TRACK FOR TODAY WITH ADDITIONAL LIGHT
ACCUMULATION. ATTENTION ALSO IS ON PORTER COUNTY INDIANA WHERE
TEMPORARY BUT MORE APPRECIABLE LAKE ENHANCED SNOW SHOWERS ARE
EXPECTED AT TIMES TODAY AND TONIGHT. AT THIS TIME NO HEADLINES ARE
PLANNED TO BE ISSUED AS ONLY MINIMAL IMPACTS ARE EXPECTED AT THIS
TIME AND SOME UNCERTAINTY ON DURATION. AN AREA WIDE SPECIAL
WEATHER STATEMENT WAS AGAIN ISSUED AND ONE MORE FOCUSED FOR PORTER
COUNTY. ALSO ON TRACK IS THE COLD WHICH LOOKS TO PROVIDE AREA WIDE
SUBZERO WIND CHILLS TO START WEDNESDAY MORNING AND PROBABLY
THURSDAY TOO.

THE IMPRESSIVELY AMPLIFIED TROUGH ACROSS EASTERN NORTH AMERICA IS
EVER SO SLOWLY INCHING EASTWARD. WITH A VIGOROUS 150KT UPPER JET
ON ITS WESTERN EDGE...THERE REMAINS NUMEROUS EMBEDDED SHORT WAVES
OVER THE WESTERN GREAT LAKES. THESE DISTURBANCES AND THEIR LIFT
WITH CONTINUED LOW-LEVEL COLD ADVECTION AND STEEP LAPSE RATES WILL
HELP THE SNOW TO CONTINUE TODAY. THE LAPSE RATES WILL ALLOW FOR
OCCASIONAL SNOW SHOWERS WHICH WILL BRING SHARPLY REDUCED
VISIBILITY AND SWATHS OF SLIGHTLY HIGHER SNOWFALL AMOUNTS. A
GENERAL WEST-TO-EAST FADE IN THIS SYNOPTIC ACTIVITY IS EXPECTED
LATE THIS AFTERNOON THROUGH MID-EVENING. HIGH TEMPERATURES WILL
REBOUND LITTLE IF AT ALL TODAY WITH MID TEENS TO MID 20S EXPECTED
FROM WEST TO EAST WITH WIND GUSTS TO 25 MPH ADDING AN EXTRA CHILL
TO THE AIR.

AS FOR LAKE EFFECT SNOW IN NORTHWEST INDIANA...THE COLD ADVECTION
IN THE LOW LEVELS...CHARACTERIZED BY 850MB TEMPERATURES DROPPING
TO -15C OR COLDER BY EARLY AFTERNOON...WILL HELP STRENGTHEN LAKE-
INDUCED INSTABILITY. MODIFIED RAP AND NAM SOUNDINGS FOR MID 30S
SURFACE TEMPERATURES PROVIDE CAPE OF 50 J/KG MUCH OF TODAY. BOTH
OF THESE MODELS INDICATE TRANSIENT BUT STRONG LOW-LEVEL OMEGA INTO
PORTER COUNTY TODAY AND EARLY THIS EVENING. THE ACTIVITY IS LIKELY
TO BE SOMEWHAT DISORGANIZED DUE TO A LACK OF A CONFLUENT
FOCUS...BUT STILL ENOUGH OF A DURATION TO PROVIDE 12-24 HOUR
SNOWFALL TOTALS OF 2-3 POSSIBLY 4 INCHES TODAY AND TONIGHT...WITH
THE HIGHER END IN NORTHEAST PORTER. THE BETTER SIGNAL FOR THE
CONFLUENT FLOW REMAINS JUST EAST OF OUR AREA WHERE ADVISORIES WILL
GO INTO EFFECT FROM ADJACENT NWS NORTHERN INDIANA DURING THE MID-
AFTERNOON.

THE STRONG CYCLONIC FLOW STILL IN PLACE TONIGHT SHOULD WARRANT
CLOUDS THOUGH SOME BREAKS COULD HAPPEN IN NORTHERN ILLINOIS BY
DAYBREAK WEDNESDAY. THE 4KM SPC WRF COLUMN CONDENSATE FIELD WHICH
OFTEN DOES WELL WITH CAA STRATOCU KEEPS CLOUDS AROUND A GOOD PART
OF THE NIGHT AS WELL...LENDING TO A LITTLE HIGHER CONFIDENCE.
TEMPERATURES WILL STILL FALL WITHIN THIS REGIME AND SINGLE DIGITS
ARE EXPECTED IN MOST LOCATIONS BY DAYBREAK WEDNESDAY. THE
CONFIDENCE IN CLOUD COVER DROPS QUITE A BIT WEDNESDAY AND
WEDNESDAY NIGHT THOUGH DO ANTICIPATE A GENERAL DIMINISHING TREND
WHICH WILL ALLOW FOR WEDNESDAY NIGHT TO BE A CHILLY ONE...WITH
SOME OUTLYING NEAR OR EVEN SUBZERO LOWS POSSIBLE.

SNOW IS NOT EXPECTED FOR THE AREA ON WEDNESDAY OUTSIDE OF SOME
CONTINUED LIGHTER LAKE EFFECT SNOW SHOWERS IN NORTHERN PORTER
COUNTY...ALTHOUGH THE BOUNDARY LAYER FLOW WILL BE GRADUALLY
BACKING SO IT IS NOT ANTICIPATED TO BE MUCH.

MTF

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

WINTER CONTINUES GOING FORWARD INTO THE WEEKEND AND EARLY NEXT
WEEK IN AN UNSETTLED PATTERN. GLOBAL GUIDANCE CONTINUES TO SHOW A
SHEARED SHORT WAVE DIVING OVER OR NEAR THE AREA IN NORTHWEST FLOW.
MOST MODELS AND EVEN ENSEMBLE MEMBERS INDICATE LIGHT QPF WITH
THIS. IT IS A FEW DAYS AWAY YET BUT IT HAS THE LOOK OF ONE OF
THOSE CLIPPER-LIKE SYSTEMS THAT COULD PRODUCE A NARROW SWATH OF
POSSIBLY A COUPLE INCHES OF SNOW GIVEN FAVORABLE THERMAL PROFILES
FOR SNOW GROWTH AND LIGHT LOW-LEVEL WINDS.

THE NORTHERN STREAM OF THE JET AGAIN BUCKLES BEHIND THE
AFOREMENTIONED WAVE WITH AN ARCTIC HIGH OF 1040MB + EXPECTED
ACROSS THE UPPER MISSISSIPPI VALLEY BY FRIDAY NIGHT. THE SYNOPTIC
REGIME CONTINUES TO RESEMBLE ONE THAT COULD SUPPORT MESOSCALE LAKE
EFFECT SNOW...POSSIBLY EVEN HEAVY...WITH CONVERGENCE POINTED
TOWARD SOME OF THE CWA. AT THIS TIME THAT LOOKS TO BE MORE
NORTHWEST INDIANA. AGAIN FAR TOO EARLY FOR SOMETHING OF THAT SCALE
TO HAVE BIG CONFIDENCE IN...BUT DID INCREASE SNOW CHANCES IN FAR
NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY.

MTF

&&

.AVIATION...
FOR THE 18Z TAFS...

EXPECT LIGHT SNOW SHOWERS/FLURRIES TO CONTINUE OFF AND ON THROUGH
THE REMAINDER OF THE AFTERNOON THOUGH AT LEAST FOR THE NEXT FEW
HOURS EXPECT VARIABLE HIGH END MVFR TO VFR CONDITIONS WITH LOWER
CHANCES FOR IFR. RAP/HRRR MODELS CONTINUE TO HINT AT AN UPTICK IN
ACTIVITY THIS EVENING SO ADJUSTED TIMING OF THE TEMPO TO FIT THE
BEST WINDOW OF IFR OR NEAR IFR CONDITIONS. FORECAST SOUNDINGS SHOW
A DEEP SATURATED LAYER WITHIN THE SNOW GROWTH ZONE MEANING THE
ATMOSPHERE WILL BE PRIMED TO PRODUCE DECENT SIZED DENDRITES...
HOWEVER THERE IS NO SIGNIFICANT SOURCE OF FORCING. THAT
SAID...PROBABLY WONT TAKE MUCH TO SQUEEZE OUT SOME SNOW THIS
EVENING AND AN UPPER LEVEL DISTURBANCE IS PROGGED TO DROP INTO THE
NORTHERN GREAT LAKES REGION THIS EVENING WITH MODEST MID LEVEL
HEIGHT FALLS AS FAR SOUTH AS CHICAGOLAND. KEYING IN ON THIS TO
TIME THE POSSIBILITY FOR CONDITIONS TO LOWER AGAIN...HOWEVER
CONFIDENCE IN THE DETAILS REMAINS LOW AT THIS TIME GIVEN THE VERY
BENIGN FORCING. WINDS ARE EXPECTED TO REMAIN OUT OF THE NORTHWEST
THROUGH THE PERIOD WITH GUSTS TO AROUND 20 KT MUCH OF THE TIME.

BMD

&&

.MARINE...
218 PM CST

A MODERATELY STRONG NORTH TO NORTHWESTERLY GRADIENT PERSISTS
ACROSS LAKE MICHIGAN BETWEEN AN AREA OF LOW PRESSURE OVER THE
EASTERN GREAT LAKES AND STRONG HIGH PRESSURE OVER THE PLAINS. LOW
END GALES ARE EXPECTED TO CONTINUE MAINLY ACROSS THE NORTH HALF OF
THE LAKE THROUGH MID MORNING WEDNESDAY. THE COMBINATION OF COLD
TEMPERATURES OVER THE LAKE AND 30 TO 35 KT WINDS WILL RESULT IN
SOME FREEZING SPRAY AS WELL. WINDS BRIEFLY DIMINISH AND BACK TO
WEST-NORTHWEST THURSDAY AS THE RIDGE NOSES CLOSER AND THE GRADIENT
RELAXES...HOWEVER ANOTHER LOW IS PROGGED TO FORM OVER THE NORTHERN
GREAT LAKES THURSDAY AND WILL PUSH ANOTHER ARCTIC FRONT ACROSS
LAKE MICHIGAN ON FRIDAY. NORTHERLY WINDS ONCE AGAIN INCREASE BACK
TO AT LEAST 30 KT AND CANNOT RULE OUT SOME GALES FRIDAY NIGHT INTO
EARLY SATURDAY...ALONG WITH FREEZING SPRAY AS BITTERLY COLD AIR
MOVES ACROSS THE REGION.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 091745
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1145 AM CST TUE FEB 9 2016

.SHORT TERM...
334 AM CST

THROUGH THURSDAY...

THE FORECAST THEME OF LIGHT SNOW WITH OCCASIONAL MODERATE SNOW
SHOWERS REMAINS ON TRACK FOR TODAY WITH ADDITIONAL LIGHT
ACCUMULATION. ATTENTION ALSO IS ON PORTER COUNTY INDIANA WHERE
TEMPORARY BUT MORE APPRECIABLE LAKE ENHANCED SNOW SHOWERS ARE
EXPECTED AT TIMES TODAY AND TONIGHT. AT THIS TIME NO HEADLINES ARE
PLANNED TO BE ISSUED AS ONLY MINIMAL IMPACTS ARE EXPECTED AT THIS
TIME AND SOME UNCERTAINTY ON DURATION. AN AREA WIDE SPECIAL
WEATHER STATEMENT WAS AGAIN ISSUED AND ONE MORE FOCUSED FOR PORTER
COUNTY. ALSO ON TRACK IS THE COLD WHICH LOOKS TO PROVIDE AREA WIDE
SUBZERO WIND CHILLS TO START WEDNESDAY MORNING AND PROBABLY
THURSDAY TOO.

THE IMPRESSIVELY AMPLIFIED TROUGH ACROSS EASTERN NORTH AMERICA IS
EVER SO SLOWLY INCHING EASTWARD. WITH A VIGOROUS 150KT UPPER JET
ON ITS WESTERN EDGE...THERE REMAINS NUMEROUS EMBEDDED SHORT WAVES
OVER THE WESTERN GREAT LAKES. THESE DISTURBANCES AND THEIR LIFT
WITH CONTINUED LOW-LEVEL COLD ADVECTION AND STEEP LAPSE RATES WILL
HELP THE SNOW TO CONTINUE TODAY. THE LAPSE RATES WILL ALLOW FOR
OCCASIONAL SNOW SHOWERS WHICH WILL BRING SHARPLY REDUCED
VISIBILITY AND SWATHS OF SLIGHTLY HIGHER SNOWFALL AMOUNTS. A
GENERAL WEST-TO-EAST FADE IN THIS SYNOPTIC ACTIVITY IS EXPECTED
LATE THIS AFTERNOON THROUGH MID-EVENING. HIGH TEMPERATURES WILL
REBOUND LITTLE IF AT ALL TODAY WITH MID TEENS TO MID 20S EXPECTED
FROM WEST TO EAST WITH WIND GUSTS TO 25 MPH ADDING AN EXTRA CHILL
TO THE AIR.

AS FOR LAKE EFFECT SNOW IN NORTHWEST INDIANA...THE COLD ADVECTION
IN THE LOW LEVELS...CHARACTERIZED BY 850MB TEMPERATURES DROPPING
TO -15C OR COLDER BY EARLY AFTERNOON...WILL HELP STRENGTHEN LAKE-
INDUCED INSTABILITY. MODIFIED RAP AND NAM SOUNDINGS FOR MID 30S
SURFACE TEMPERATURES PROVIDE CAPE OF 50 J/KG MUCH OF TODAY. BOTH
OF THESE MODELS INDICATE TRANSIENT BUT STRONG LOW-LEVEL OMEGA INTO
PORTER COUNTY TODAY AND EARLY THIS EVENING. THE ACTIVITY IS LIKELY
TO BE SOMEWHAT DISORGANIZED DUE TO A LACK OF A CONFLUENT
FOCUS...BUT STILL ENOUGH OF A DURATION TO PROVIDE 12-24 HOUR
SNOWFALL TOTALS OF 2-3 POSSIBLY 4 INCHES TODAY AND TONIGHT...WITH
THE HIGHER END IN NORTHEAST PORTER. THE BETTER SIGNAL FOR THE
CONFLUENT FLOW REMAINS JUST EAST OF OUR AREA WHERE ADVISORIES WILL
GO INTO EFFECT FROM ADJACENT NWS NORTHERN INDIANA DURING THE MID-
AFTERNOON.

THE STRONG CYCLONIC FLOW STILL IN PLACE TONIGHT SHOULD WARRANT
CLOUDS THOUGH SOME BREAKS COULD HAPPEN IN NORTHERN ILLINOIS BY
DAYBREAK WEDNESDAY. THE 4KM SPC WRF COLUMN CONDENSATE FIELD WHICH
OFTEN DOES WELL WITH CAA STRATOCU KEEPS CLOUDS AROUND A GOOD PART
OF THE NIGHT AS WELL...LENDING TO A LITTLE HIGHER CONFIDENCE.
TEMPERATURES WILL STILL FALL WITHIN THIS REGIME AND SINGLE DIGITS
ARE EXPECTED IN MOST LOCATIONS BY DAYBREAK WEDNESDAY. THE
CONFIDENCE IN CLOUD COVER DROPS QUITE A BIT WEDNESDAY AND
WEDNESDAY NIGHT THOUGH DO ANTICIPATE A GENERAL DIMINISHING TREND
WHICH WILL ALLOW FOR WEDNESDAY NIGHT TO BE A CHILLY ONE...WITH
SOME OUTLYING NEAR OR EVEN SUBZERO LOWS POSSIBLE.

SNOW IS NOT EXPECTED FOR THE AREA ON WEDNESDAY OUTSIDE OF SOME
CONTINUED LIGHTER LAKE EFFECT SNOW SHOWERS IN NORTHERN PORTER
COUNTY...ALTHOUGH THE BOUNDARY LAYER FLOW WILL BE GRADUALLY
BACKING SO IT IS NOT ANTICIPATED TO BE MUCH.

MTF

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

WINTER CONTINUES GOING FORWARD INTO THE WEEKEND AND EARLY NEXT
WEEK IN AN UNSETTLED PATTERN. GLOBAL GUIDANCE CONTINUES TO SHOW A
SHEARED SHORT WAVE DIVING OVER OR NEAR THE AREA IN NORTHWEST FLOW.
MOST MODELS AND EVEN ENSEMBLE MEMBERS INDICATE LIGHT QPF WITH
THIS. IT IS A FEW DAYS AWAY YET BUT IT HAS THE LOOK OF ONE OF
THOSE CLIPPER-LIKE SYSTEMS THAT COULD PRODUCE A NARROW SWATH OF
POSSIBLY A COUPLE INCHES OF SNOW GIVEN FAVORABLE THERMAL PROFILES
FOR SNOW GROWTH AND LIGHT LOW-LEVEL WINDS.

THE NORTHERN STREAM OF THE JET AGAIN BUCKLES BEHIND THE
AFOREMENTIONED WAVE WITH AN ARCTIC HIGH OF 1040MB + EXPECTED
ACROSS THE UPPER MISSISSIPPI VALLEY BY FRIDAY NIGHT. THE SYNOPTIC
REGIME CONTINUES TO RESEMBLE ONE THAT COULD SUPPORT MESOSCALE LAKE
EFFECT SNOW...POSSIBLY EVEN HEAVY...WITH CONVERGENCE POINTED
TOWARD SOME OF THE CWA. AT THIS TIME THAT LOOKS TO BE MORE
NORTHWEST INDIANA. AGAIN FAR TOO EARLY FOR SOMETHING OF THAT SCALE
TO HAVE BIG CONFIDENCE IN...BUT DID INCREASE SNOW CHANCES IN FAR
NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY.

MTF

&&

.AVIATION...
FOR THE 18Z TAFS...

EXPECT LIGHT SNOW SHOWERS/FLURRIES TO CONTINUE OFF AND ON THROUGH
THE REMAINDER OF THE AFTERNOON THOUGH AT LEAST FOR THE NEXT FEW
HOURS EXPECT VARIABLE HIGH END MVFR TO VFR CONDITIONS WITH LOWER
CHANCES FOR IFR. RAP/HRRR MODELS CONTINUE TO HINT AT AN UPTICK IN
ACTIVITY THIS EVENING SO ADJUSTED TIMING OF THE TEMPO TO FIT THE
BEST WINDOW OF IFR OR NEAR IFR CONDITIONS. FORECAST SOUNDINGS SHOW
A DEEP SATURATED LAYER WITHIN THE SNOW GROWTH ZONE MEANING THE
ATMOSPHERE WILL BE PRIMED TO PRODUCE DECENT SIZED DENDRITES...
HOWEVER THERE IS NO SIGNIFICANT SOURCE OF FORCING. THAT
SAID...PROBABLY WONT TAKE MUCH TO SQUEEZE OUT SOME SNOW THIS
EVENING AND AN UPPER LEVEL DISTURBANCE IS PROGGED TO DROP INTO THE
NORTHERN GREAT LAKES REGION THIS EVENING WITH MODEST MID LEVEL
HEIGHT FALLS AS FAR SOUTH AS CHICAGOLAND. KEYING IN ON THIS TO
TIME THE POSSIBILITY FOR CONDITIONS TO LOWER AGAIN...HOWEVER
CONFIDENCE IN THE DETAILS REMAINS LOW AT THIS TIME GIVEN THE VERY
BENIGN FORCING. WINDS ARE EXPECTED TO REMAIN OUT OF THE NORTHWEST
THROUGH THE PERIOD WITH GUSTS TO AROUND 20 KT MUCH OF THE TIME.

BMD

&&

.MARINE...
258 AM CST

ISSUED A GALE WARNING FOR THE NORTHERN TWO THIRDS OF THE LAKE FROM
MID MORNING THROUGH EARLY WEDNESDAY MORNING. CONFIDENCE IS  JUST
HIGH ENOUGH TO ISSUE THE WARNING...BUT HAVE HIGH CONFIDENCE THAT ANY
GALES WILL BE ON THE LOW END OF THE SPECTRUM.  NO CHANGES WERE MADE
TO THE SMALL CRAFT ADVISORY WHICH GOES THROUGH THROUGH EARLY
WEDNESDAY NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY
MORNING FOR THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND
WAVES.

A WEAK LOW OVER LAKE ONTARIO REACHES NEW ENGLAND THIS EVENING...AND
THEN MERGES WITH A DEEPER LOW OVER THE ATLANTIC WEDNESDAY EVENING.
MEANWHILE HIGH PRESSURE OVER THE NORTHERN PLAINS WILL BUILD SOUTH
TIGHTENING THE PRESSURE GRADIENT OVER THE WESTERN GREAT LAKES.
NORTHWEST WINDS INCREASE TO LOW END GALES THIS MORNING AND PERSIST
INTO WEDNESDAY MORNING MAINLY ACROSS THE NORTHERN TWO THIRDS OF THE
LAKE.  OCCASIONAL GALES ARE POSSIBLE OVER THE SOUTHERN THIRD OF THE
LAKE TONIGHT INTO WEDNESDAY MORNING. DO NOT HAVE ENOUGH CONFIDENCE
IN A PROLONGED PERIOD OF GALE FORCE GUSTS TO HOIST A GALE WARNING
FOR THE SOUTHERN THIRD OF THE LAKE.

THE HIGH PASSES SOUTH OF THE LAKE THURSDAY EVENING AND WINDS WILL
BECOME WEST 15-25 KT.  A WEAK LOW FORMS OVER ONTARIO THURSDAY
EVENING AND REACHES NEW ENGLAND FRIDAY EVENING.  AT THE SAME TIME A
LARGE HIGH SPREADS OVER THE NORTHERN AND CENTRAL PLAINS. THIS WILL
LEAD TO NORTHWEST TO NORTH WINDS INCREASING TO AT LEAST 30 KT FRIDAY
AFTERNOON THROUGH SATURDAY MORNING.  THE HIGH MOVES OVER THE LAKE
SATURDAY EVENING AND CONTINUES EAST TO THE EASTERN GREAT LAKES
SUNDAY MORNING. WINDS BECOME SOUTH IN THE WAKE OF THE HIGH SUNDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 091145
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
545 AM CST TUE FEB 9 2016

.SHORT TERM...
334 AM CST

THROUGH THURSDAY...

THE FORECAST THEME OF LIGHT SNOW WITH OCCASIONAL MODERATE SNOW
SHOWERS REMAINS ON TRACK FOR TODAY WITH ADDITIONAL LIGHT
ACCUMULATION. ATTENTION ALSO IS ON PORTER COUNTY INDIANA WHERE
TEMPORARY BUT MORE APPRECIABLE LAKE ENHANCED SNOW SHOWERS ARE
EXPECTED AT TIMES TODAY AND TONIGHT. AT THIS TIME NO HEADLINES ARE
PLANNED TO BE ISSUED AS ONLY MINIMAL IMPACTS ARE EXPECTED AT THIS
TIME AND SOME UNCERTAINTY ON DURATION. AN AREA WIDE SPECIAL
WEATHER STATEMENT WAS AGAIN ISSUED AND ONE MORE FOCUSED FOR PORTER
COUNTY. ALSO ON TRACK IS THE COLD WHICH LOOKS TO PROVIDE AREA WIDE
SUBZERO WIND CHILLS TO START WEDNESDAY MORNING AND PROBABLY
THURSDAY TOO.

THE IMPRESSIVELY AMPLIFIED TROUGH ACROSS EASTERN NORTH AMERICA IS
EVER SO SLOWLY INCHING EASTWARD. WITH A VIGOROUS 150KT UPPER JET
ON ITS WESTERN EDGE...THERE REMAINS NUMEROUS EMBEDDED SHORT WAVES
OVER THE WESTERN GREAT LAKES. THESE DISTURBANCES AND THEIR LIFT
WITH CONTINUED LOW-LEVEL COLD ADVECTION AND STEEP LAPSE RATES WILL
HELP THE SNOW TO CONTINUE TODAY. THE LAPSE RATES WILL ALLOW FOR
OCCASIONAL SNOW SHOWERS WHICH WILL BRING SHARPLY REDUCED
VISIBILITY AND SWATHS OF SLIGHTLY HIGHER SNOWFALL AMOUNTS. A
GENERAL WEST-TO-EAST FADE IN THIS SYNOPTIC ACTIVITY IS EXPECTED
LATE THIS AFTERNOON THROUGH MID-EVENING. HIGH TEMPERATURES WILL
REBOUND LITTLE IF AT ALL TODAY WITH MID TEENS TO MID 20S EXPECTED
FROM WEST TO EAST WITH WIND GUSTS TO 25 MPH ADDING AN EXTRA CHILL
TO THE AIR.

AS FOR LAKE EFFECT SNOW IN NORTHWEST INDIANA...THE COLD ADVECTION
IN THE LOW LEVELS...CHARACTERIZED BY 850MB TEMPERATURES DROPPING
TO -15C OR COLDER BY EARLY AFTERNOON...WILL HELP STRENGTHEN LAKE-
INDUCED INSTABILITY. MODIFIED RAP AND NAM SOUNDINGS FOR MID 30S
SURFACE TEMPERATURES PROVIDE CAPE OF 50 J/KG MUCH OF TODAY. BOTH
OF THESE MODELS INDICATE TRANSIENT BUT STRONG LOW-LEVEL OMEGA INTO
PORTER COUNTY TODAY AND EARLY THIS EVENING. THE ACTIVITY IS LIKELY
TO BE SOMEWHAT DISORGANIZED DUE TO A LACK OF A CONFLUENT
FOCUS...BUT STILL ENOUGH OF A DURATION TO PROVIDE 12-24 HOUR
SNOWFALL TOTALS OF 2-3 POSSIBLY 4 INCHES TODAY AND TONIGHT...WITH
THE HIGHER END IN NORTHEAST PORTER. THE BETTER SIGNAL FOR THE
CONFLUENT FLOW REMAINS JUST EAST OF OUR AREA WHERE ADVISORIES WILL
GO INTO EFFECT FROM ADJACENT NWS NORTHERN INDIANA DURING THE MID-
AFTERNOON.

THE STRONG CYCLONIC FLOW STILL IN PLACE TONIGHT SHOULD WARRANT
CLOUDS THOUGH SOME BREAKS COULD HAPPEN IN NORTHERN ILLINOIS BY
DAYBREAK WEDNESDAY. THE 4KM SPC WRF COLUMN CONDENSATE FIELD WHICH
OFTEN DOES WELL WITH CAA STRATOCU KEEPS CLOUDS AROUND A GOOD PART
OF THE NIGHT AS WELL...LENDING TO A LITTLE HIGHER CONFIDENCE.
TEMPERATURES WILL STILL FALL WITHIN THIS REGIME AND SINGLE DIGITS
ARE EXPECTED IN MOST LOCATIONS BY DAYBREAK WEDNESDAY. THE
CONFIDENCE IN CLOUD COVER DROPS QUITE A BIT WEDNESDAY AND
WEDNESDAY NIGHT THOUGH DO ANTICIPATE A GENERAL DIMINISHING TREND
WHICH WILL ALLOW FOR WEDNESDAY NIGHT TO BE A CHILLY ONE...WITH
SOME OUTLYING NEAR OR EVEN SUBZERO LOWS POSSIBLE.

SNOW IS NOT EXPECTED FOR THE AREA ON WEDNESDAY OUTSIDE OF SOME
CONTINUED LIGHTER LAKE EFFECT SNOW SHOWERS IN NORTHERN PORTER
COUNTY...ALTHOUGH THE BOUNDARY LAYER FLOW WILL BE GRADUALLY
BACKING SO IT IS NOT ANTICIPATED TO BE MUCH.

MTF

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

WINTER CONTINUES GOING FORWARD INTO THE WEEKEND AND EARLY NEXT
WEEK IN AN UNSETTLED PATTERN. GLOBAL GUIDANCE CONTINUES TO SHOW A
SHEARED SHORT WAVE DIVING OVER OR NEAR THE AREA IN NORTHWEST FLOW.
MOST MODELS AND EVEN ENSEMBLE MEMBERS INDICATE LIGHT QPF WITH
THIS. IT IS A FEW DAYS AWAY YET BUT IT HAS THE LOOK OF ONE OF
THOSE CLIPPER-LIKE SYSTEMS THAT COULD PRODUCE A NARROW SWATH OF
POSSIBLY A COUPLE INCHES OF SNOW GIVEN FAVORABLE THERMAL PROFILES
FOR SNOW GROWTH AND LIGHT LOW-LEVEL WINDS.

THE NORTHERN STREAM OF THE JET AGAIN BUCKLES BEHIND THE
AFOREMENTIONED WAVE WITH AN ARCTIC HIGH OF 1040MB + EXPECTED
ACROSS THE UPPER MISSISSIPPI VALLEY BY FRIDAY NIGHT. THE SYNOPTIC
REGIME CONTINUES TO RESEMBLE ONE THAT COULD SUPPORT MESOSCALE LAKE
EFFECT SNOW...POSSIBLY EVEN HEAVY...WITH CONVERGENCE POINTED
TOWARD SOME OF THE CWA. AT THIS TIME THAT LOOKS TO BE MORE
NORTHWEST INDIANA. AGAIN FAR TOO EARLY FOR SOMETHING OF THAT SCALE
TO HAVE BIG CONFIDENCE IN...BUT DID INCREASE SNOW CHANCES IN FAR
NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY.

MTF

&&

.AVIATION...
FOR THE 12Z TAFS...

LIGHT SNOW WILL CONTINUE INTO THIS EVENING WITH MINOR
ACCUMULATIONS OF 1-2 INCHES EXPECTED. LOW END VFR/HIGH END MVFR
CIGS ARE EXPECTED THROUGH THE PERIOD ALONG WITH GUSTY NW WINDS.
HAVE HIGH CONFIDENCE THAT WINDS WILL NOT BECOME MORE NORTH THAN
320 DEGREES. ON THE OTHER HAND...HAVE MEDIUM-LOW CONFIDENCE IN
SNOW INTENSITY THIS AFTN. GUIDANCE FEATURES INCREASING
FORCING...SO KEPT A TEMPO FOR IFR VSBY WITH MODERATE SNOW SHOWERS.
SNOW TAPERS OFF FROM WEST TO EAST THIS EVENING WITH VFR CIGS.
GUSTY NW WINDS CONTINUE OVERNIGHT INTO WEDNESDAY.

CONFIDENCE SUMMARY...HIGH CONFIDENCE IN LIGHT SNOW INTO THIS
EVENING AND GUSTY NW WINDS. MEDIUM CONFIDENCE IN MVFR CIGS...AND
MEDIUM- LOW CONFIDENCE IN TIMING AND OCCURRENCE OF MODERATE SNOW
SHOWERS THIS AFTN.

JEE

&&

.MARINE...
258 AM CST

ISSUED A GALE WARNING FOR THE NORTHERN TWO THIRDS OF THE LAKE FROM
MID MORNING THROUGH EARLY WEDNESDAY MORNING. CONFIDENCE IS  JUST
HIGH ENOUGH TO ISSUE THE WARNING...BUT HAVE HIGH CONFIDENCE THAT ANY
GALES WILL BE ON THE LOW END OF THE SPECTRUM.  NO CHANGES WERE MADE
TO THE SMALL CRAFT ADVISORY WHICH GOES THROUGH THROUGH EARLY
WEDNESDAY NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY
MORNING FOR THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND
WAVES.

A WEAK LOW OVER LAKE ONTARIO REACHES NEW ENGLAND THIS EVENING...AND
THEN MERGES WITH A DEEPER LOW OVER THE ATLANTIC WEDNESDAY EVENING.
MEANWHILE HIGH PRESSURE OVER THE NORTHERN PLAINS WILL BUILD SOUTH
TIGHTENING THE PRESSURE GRADIENT OVER THE WESTERN GREAT LAKES.
NORTHWEST WINDS INCREASE TO LOW END GALES THIS MORNING AND PERSIST
INTO WEDNESDAY MORNING MAINLY ACROSS THE NORTHERN TWO THIRDS OF THE
LAKE.  OCCASIONAL GALES ARE POSSIBLE OVER THE SOUTHERN THIRD OF THE
LAKE TONIGHT INTO WEDNESDAY MORNING. DO NOT HAVE ENOUGH CONFIDENCE
IN A PROLONGED PERIOD OF GALE FORCE GUSTS TO HOIST A GALE WARNING
FOR THE SOUTHERN THIRD OF THE LAKE.

THE HIGH PASSES SOUTH OF THE LAKE THURSDAY EVENING AND WINDS WILL
BECOME WEST 15-25 KT.  A WEAK LOW FORMS OVER ONTARIO THURSDAY
EVENING AND REACHES NEW ENGLAND FRIDAY EVENING.  AT THE SAME TIME A
LARGE HIGH SPREADS OVER THE NORTHERN AND CENTRAL PLAINS. THIS WILL
LEAD TO NORTHWEST TO NORTH WINDS INCREASING TO AT LEAST 30 KT FRIDAY
AFTERNOON THROUGH SATURDAY MORNING.  THE HIGH MOVES OVER THE LAKE
SATURDAY EVENING AND CONTINUES EAST TO THE EASTERN GREAT LAKES
SUNDAY MORNING. WINDS BECOME SOUTH IN THE WAKE OF THE HIGH SUNDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 090945
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
345 AM CST TUE FEB 9 2016

.SHORT TERM...
334 AM CST

THROUGH THURSDAY...

THE FORECAST THEME OF LIGHT SNOW WITH OCCASIONAL MODERATE SNOW
SHOWERS REMAINS ON TRACK FOR TODAY WITH ADDITIONAL LIGHT
ACCUMULATION. ATTENTION ALSO IS ON PORTER COUNTY INDIANA WHERE
TEMPORARY BUT MORE APPRECIABLE LAKE ENHANCED SNOW SHOWERS ARE
EXPECTED AT TIMES TODAY AND TONIGHT. AT THIS TIME NO HEADLINES ARE
PLANNED TO BE ISSUED AS ONLY MINIMAL IMPACTS ARE EXPECTED AT THIS
TIME AND SOME UNCERTAINTY ON DURATION. AN AREA WIDE SPECIAL
WEATHER STATEMENT WAS AGAIN ISSUED AND ONE MORE FOCUSED FOR PORTER
COUNTY. ALSO ON TRACK IS THE COLD WHICH LOOKS TO PROVIDE AREA WIDE
SUBZERO WIND CHILLS TO START WEDNESDAY MORNING AND PROBABLY
THURSDAY TOO.

THE IMPRESSIVELY AMPLIFIED TROUGH ACROSS EASTERN NORTH AMERICA IS
EVER SO SLOWLY INCHING EASTWARD. WITH A VIGOROUS 150KT UPPER JET
ON ITS WESTERN EDGE...THERE REMAINS NUMEROUS EMBEDDED SHORT WAVES
OVER THE WESTERN GREAT LAKES. THESE DISTURBANCES AND THEIR LIFT
WITH CONTINUED LOW-LEVEL COLD ADVECTION AND STEEP LAPSE RATES WILL
HELP THE SNOW TO CONTINUE TODAY. THE LAPSE RATES WILL ALLOW FOR
OCCASIONAL SNOW SHOWERS WHICH WILL BRING SHARPLY REDUCED
VISIBILITY AND SWATHS OF SLIGHTLY HIGHER SNOWFALL AMOUNTS. A
GENERAL WEST-TO-EAST FADE IN THIS SYNOPTIC ACTIVITY IS EXPECTED
LATE THIS AFTERNOON THROUGH MID-EVENING. HIGH TEMPERATURES WILL
REBOUND LITTLE IF AT ALL TODAY WITH MID TEENS TO MID 20S EXPECTED
FROM WEST TO EAST WITH WIND GUSTS TO 25 MPH ADDING AN EXTRA CHILL
TO THE AIR.

AS FOR LAKE EFFECT SNOW IN NORTHWEST INDIANA...THE COLD ADVECTION
IN THE LOW LEVELS...CHARACTERIZED BY 850MB TEMPERATURES DROPPING
TO -15C OR COLDER BY EARLY AFTERNOON...WILL HELP STRENGTHEN LAKE-
INDUCED INSTABILITY. MODIFIED RAP AND NAM SOUNDINGS FOR MID 30S
SURFACE TEMPERATURES PROVIDE CAPE OF 50 J/KG MUCH OF TODAY. BOTH
OF THESE MODELS INDICATE TRANSIENT BUT STRONG LOW-LEVEL OMEGA INTO
PORTER COUNTY TODAY AND EARLY THIS EVENING. THE ACTIVITY IS LIKELY
TO BE SOMEWHAT DISORGANIZED DUE TO A LACK OF A CONFLUENT
FOCUS...BUT STILL ENOUGH OF A DURATION TO PROVIDE 12-24 HOUR
SNOWFALL TOTALS OF 2-3 POSSIBLY 4 INCHES TODAY AND TONIGHT...WITH
THE HIGHER END IN NORTHEAST PORTER. THE BETTER SIGNAL FOR THE
CONFLUENT FLOW REMAINS JUST EAST OF OUR AREA WHERE ADVISORIES WILL
GO INTO EFFECT FROM ADJACENT NWS NORTHERN INDIANA DURING THE MID-
AFTERNOON.

THE STRONG CYCLONIC FLOW STILL IN PLACE TONIGHT SHOULD WARRANT
CLOUDS THOUGH SOME BREAKS COULD HAPPEN IN NORTHERN ILLINOIS BY
DAYBREAK WEDNESDAY. THE 4KM SPC WRF COLUMN CONDENSATE FIELD WHICH
OFTEN DOES WELL WITH CAA STRATOCU KEEPS CLOUDS AROUND A GOOD PART
OF THE NIGHT AS WELL...LENDING TO A LITTLE HIGHER CONFIDENCE.
TEMPERATURES WILL STILL FALL WITHIN THIS REGIME AND SINGLE DIGITS
ARE EXPECTED IN MOST LOCATIONS BY DAYBREAK WEDNESDAY. THE
CONFIDENCE IN CLOUD COVER DROPS QUITE A BIT WEDNESDAY AND
WEDNESDAY NIGHT THOUGH DO ANTICIPATE A GENERAL DIMINISHING TREND
WHICH WILL ALLOW FOR WEDNESDAY NIGHT TO BE A CHILLY ONE...WITH
SOME OUTLYING NEAR OR EVEN SUBZERO LOWS POSSIBLE.

SNOW IS NOT EXPECTED FOR THE AREA ON WEDNESDAY OUTSIDE OF SOME
CONTINUED LIGHTER LAKE EFFECT SNOW SHOWERS IN NORTHERN PORTER
COUNTY...ALTHOUGH THE BOUNDARY LAYER FLOW WILL BE GRADUALLY
BACKING SO IT IS NOT ANTICIPATED TO BE MUCH.

MTF


&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

WINTER CONTINUES GOING FORWARD INTO THE WEEKEND AND EARLY NEXT
WEEK IN AN UNSETTLED PATTERN. GLOBAL GUIDANCE CONTINUES TO SHOW A
SHEARED SHORT WAVE DIVING OVER OR NEAR THE AREA IN NORTHWEST FLOW.
MOST MODELS AND EVEN ENSEMBLE MEMBERS INDICATE LIGHT QPF WITH
THIS. IT IS A FEW DAYS AWAY YET BUT IT HAS THE LOOK OF ONE OF
THOSE CLIPPER-LIKE SYSTEMS THAT COULD PRODUCE A NARROW SWATH OF
POSSIBLY A COUPLE INCHES OF SNOW GIVEN FAVORABLE THERMAL PROFILES
FOR SNOW GROWTH AND LIGHT LOW-LEVEL WINDS.

THE NORTHERN STREAM OF THE JET AGAIN BUCKLES BEHIND THE
AFOREMENTIONED WAVE WITH AN ARCTIC HIGH OF 1040MB + EXPECTED
ACROSS THE UPPER MISSISSIPPI VALLEY BY FRIDAY NIGHT. THE SYNOPTIC
REGIME CONTINUES TO RESEMBLE ONE THAT COULD SUPPORT MESOSCALE LAKE
EFFECT SNOW...POSSIBLY EVEN HEAVY...WITH CONVERGENCE POINTED
TOWARD SOME OF THE CWA. AT THIS TIME THAT LOOKS TO BE MORE
NORTHWEST INDIANA. AGAIN FAR TOO EARLY FOR SOMETHING OF THAT SCALE
TO HAVE BIG CONFIDENCE IN...BUT DID INCREASE SNOW CHANCES IN FAR
NORTHWEST INDIANA FRIDAY NIGHT INTO SATURDAY.

MTF

&&

.AVIATION...
FOR THE 06Z TAFS...

LARGE UPPER LOW CENTERED WILL CONTINUE TO INFLUENCE AVIATION
WEATHER THROUGH TUESDAY EVENING. MAIN FORECAST CONCERN AND FOCUS
CONTINUES TO BE TIMING THE BEST WINDOW OF LOWER VSBY AND POTENTIAL
ACCUMULATIONS WITH OCCASIONAL SNOW SHOWERS. GYY AND MDW LOOKS TO
BE IN FAVORED CORRIDOR THROUGH THE EARLY MORNING HOURS/09-10Z...FOR
TEMPORARY IFR AND EVEN LIFR VSBY AT TIMES. FOR ORD/DPA...GENERALLY
MVFR VSBY IN SNOW SHOWERS DURING THIS TIME...ALTHOUGH CANNOT RULE
OUT IFR VSBY AT TIMES. SHORT RANGE GUIDANCE IS PICKING UP ON A
SUBTLE WAVE THAT COULD RE-ENHANCE SNOWFALL RATES TOWARD DAYBREAK.
AGAIN...GYY SHOULD BE MOST FAVORED...EVEN WITH SOME ADDED LAKE
ENHANCEMENT POTENTIAL. RFD AREA COULD FINALLY GET INTO SOME SNOW
SHOWER ACTIVITY AFTER 07Z...AND POTENTIALLY IFR VSBY AT TIMES.

THE REST OF THE DAY TUESDAY INTO TUESDAY EVENING...STEEP LOW
LEVEL LAPSE RATES AND WEAK LIFT COULD YIELD ADDITIONAL SNOW
SHOWERS AT ANY TIME. CONTINUED TO MAINTAIN THE PROB30 GROUP
DURING THE AFTERNOON FOR IFR VSBY FROM THE PREVIOUS TAF FOR
ORD/MDW/GYY/DPA GIVEN LOWER CONFIDENCE. CONFIDENCE IS ALSO LOWER
IN CIGS...AS THERE ARE POCKETS OF VFR OVER THE AREA. GUIDANCE IS
SHOWING A SIGNAL FOR INCREASED LOW-MID MVFR CIG POTENTIAL DURING
THE AFTERNOON AND POSSIBLY INTO THE EVENING. WINDS WILL BE WEST-
NORTHWEST...WITH GUSTS IN THE 20-25 KT RANGE THIS MORNING THROUGH
TONIGHT.

RC

&&

.MARINE...
258 AM CST

ISSUED A GALE WARNING FOR THE NORTHERN TWO THIRDS OF THE LAKE FROM
MID MORNING THROUGH EARLY WEDNESDAY MORNING. CONFIDENCE IS  JUST
HIGH ENOUGH TO ISSUE THE WARNING...BUT HAVE HIGH CONFIDENCE THAT ANY
GALES WILL BE ON THE LOW END OF THE SPECTRUM.  NO CHANGES WERE MADE
TO THE SMALL CRAFT ADVISORY WHICH GOES THROUGH THROUGH EARLY
WEDNESDAY NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY
MORNING FOR THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND
WAVES.

A WEAK LOW OVER LAKE ONTARIO REACHES NEW ENGLAND THIS EVENING...AND
THEN MERGES WITH A DEEPER LOW OVER THE ATLANTIC WEDNESDAY EVENING.
MEANWHILE HIGH PRESSURE OVER THE NORTHERN PLAINS WILL BUILD SOUTH
TIGHTENING THE PRESSURE GRADIENT OVER THE WESTERN GREAT LAKES.
NORTHWEST WINDS INCREASE TO LOW END GALES THIS MORNING AND PERSIST
INTO WEDNESDAY MORNING MAINLY ACROSS THE NORTHERN TWO THIRDS OF THE
LAKE.  OCCASIONAL GALES ARE POSSIBLE OVER THE SOUTHERN THIRD OF THE
LAKE TONIGHT INTO WEDNESDAY MORNING. DO NOT HAVE ENOUGH CONFIDENCE
IN A PROLONGED PERIOD OF GALE FORCE GUSTS TO HOIST A GALE WARNING
FOR THE SOUTHERN THIRD OF THE LAKE.

THE HIGH PASSES SOUTH OF THE LAKE THURSDAY EVENING AND WINDS WILL
BECOME WEST 15-25 KT.  A WEAK LOW FORMS OVER ONTARIO THURSDAY
EVENING AND REACHES NEW ENGLAND FRIDAY EVENING.  AT THE SAME TIME A
LARGE HIGH SPREADS OVER THE NORTHERN AND CENTRAL PLAINS. THIS WILL
LEAD TO NORTHWEST TO NORTH WINDS INCREASING TO AT LEAST 30 KT FRIDAY
AFTERNOON THROUGH SATURDAY MORNING.  THE HIGH MOVES OVER THE LAKE
SATURDAY EVENING AND CONTINUES EAST TO THE EASTERN GREAT LAKES
SUNDAY MORNING. WINDS BECOME SOUTH IN THE WAKE OF THE HIGH SUNDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 090859
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
259 AM CST TUE FEB 9 2016

.UPDATE...

742 PM CST

FOR EVENING UPDATE...

MINOR ADJUSTMENTS TO FORECAST THIS EVENING...TO REFINE TRANSITION
TO HIGHER POPS WITH SNOW SHOWERS SPREADING SOUTH ACROSS THE
NORTHEAST PORTION OF THE FORECAST AREA. ALSO...WITH SOME OF THE
HIGHER REFLECTIVITY RETURNS AND SOME BRIEF 1/2-3/4SM VISIBILITIES
REPORTED HAVE ALSO BUMPED UP QPF/SNOW AMOUNTS A BIT CLOSER TO AN
INCH THROUGH MIDNIGHT ESPECIALLY ACROSS PARTS OF LAKE/EASTERN
MCHENRY AND COOK COUNTIES THIS EVENING.

SNOW SHOWERS HAVE INCREASED IN COVERAGE ACROSS NORTHEAST IL...
SOUTHERN LAKE MICHIGAN AND FAR NORTHWEST INDIANA THIS EVENING IN
RESPONSE TO A SHEARED MID-LEVEL VORT MOVING SOUTH ACROSS LAKE
MICHIGAN. THIS IS EXPECTED TO CONTINUE OVERNIGHT...WITH FORECAST
SOUNDINGS DEPICTING COOLING OF THE SATURATED LAYER ESPECIALLY
BELOW 700 MB AND DEVELOPMENT OF A DEEP DENDRITIC GROWTH ZONE IN
EXCESS OF 200 MB. WHILE FORCING IS NOT TERRIBLY STRONG...THE
THERMODYNAMIC PROFILE SHOULD PRODUCE LIGHT SNOW FAIRLY EASILY.
LIGHT SNOW WAS ALSO SPREADING SOUTHEAST ACROSS THE UPPER
MISSISSIPPI VALLEY IN ASSOCIATION WITH A MID-LEVEL SPEED MAX
DROPPING INTO THE WESTERN PERIPHERY OF THE LARGE SCALE TROUGH OVER
EASTERN NORTH AMERICA...AND LIGHT SNOW SHOULD SPREAD INTO WESTERN
PARTS OF THE FA OVERNIGHT. THUS DESPITE RELATIVELY LOW QPF VALUES
ON THE ORDER OF A FEW HUNDREDTHS OF AN INCH IN ANY GIVEN PERIOD
HAVE CARRIED RELATIVELY HIGH POPS FOR LIGHT SNOW/SNOW SHOWERS INTO
TUESDAY.

OTHERWISE...FORECAST IN GOOD SHAPE WITH ONLY MINOR TWEAKS MADE PER
HOURLY OBS TRENDS EARLY THIS EVENING.

RATZER

&&

.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
300 PM CST

WEDNESDAY NIGHT THROUGH MONDAY...

BELOW NORMAL TEMPERATURES TO CONTINUE INTO THE WEEKEND AS LARGE
SCALE UPPER TROUGH OVER EASTERN NORTH AMERICA SHIFTS SLOWLY
EAST...BUT IS REINFORCED OVER THE WEEKEND BY ANOTHER CLOSED LOW
WHICH DEVELOPS OVER NEW ENGLAND/QUEBEC. EVENTUALLY THE TROUGH AXIS
SHIFTS FAR ENOUGH TO THE EAST FOR SOME MODERATION SUNDAY NIGHT
INTO MONDAY. STRONG NORTHWESTERLY FLOW ALOFT DOWNSTREAM OF
WESTERN/CENTRAL CONUS RIDGING WILL LIKELY SEE SEVERAL MINOR SHORT
WAVES RIPPLING THROUGH THE FLOW. DIFFERENCES REMAIN IN LONGER
RANGE GUIDANCE WITH LOCATION OF LOW LEVEL BAROCLINIC ZONE TO OUR
SOUTHWEST...THOUGH THE 00Z/12Z ECMWF HAVE MAINTAINED CONTINUITY IN
A MINOR DISTURBANCE TRACKING ACROSS THE MIDWEST FRIDAY WITH THE
POTENTIAL FOR SOME LIGHT SNOW. DEPENDING ON HOW QUICKLY HIGH
PRESSURE EXITS IN THE DAY 6-7 PERIOD THERE IS ALSO A CHANCE OF
LIGHT SNOW AS WARM ADVECTION DEVELOPS MONDAY. UNTIL THEN... COLD
IS THE RULE WITH OVERNIGHT LOWS IN THE SINGLE DIGITS (AND POSSIBLE
AROUND ZERO OR BELOW) AND HIGHS IN THE TEENS TO LOW 20S BEFORE
SLIGHT MODERATION TOWARD THE END OF THE FORECAST.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

LARGE UPPER LOW CENTERED WILL CONTINUE TO INFLUENCE AVIATION
WEATHER THROUGH TUESDAY EVENING. MAIN FORECAST CONCERN AND FOCUS
CONTINUES TO BE TIMING THE BEST WINDOW OF LOWER VSBY AND POTENTIAL
ACCUMULATIONS WITH OCCASIONAL SNOW SHOWERS. GYY AND MDW LOOKS TO
BE IN FAVORED CORRIDOR THROUGH THE EARLY MORNING HOURS/09-10Z...FOR
TEMPORARY IFR AND EVEN LIFR VSBY AT TIMES. FOR ORD/DPA...GENERALLY
MVFR VSBY IN SNOW SHOWERS DURING THIS TIME...ALTHOUGH CANNOT RULE
OUT IFR VSBY AT TIMES. SHORT RANGE GUIDANCE IS PICKING UP ON A
SUBTLE WAVE THAT COULD RE-ENHANCE SNOWFALL RATES TOWARD DAYBREAK.
AGAIN...GYY SHOULD BE MOST FAVORED...EVEN WITH SOME ADDED LAKE
ENHANCEMENT POTENTIAL. RFD AREA COULD FINALLY GET INTO SOME SNOW
SHOWER ACTIVITY AFTER 07Z...AND POTENTIALLY IFR VSBY AT TIMES.

THE REST OF THE DAY TUESDAY INTO TUESDAY EVENING...STEEP LOW
LEVEL LAPSE RATES AND WEAK LIFT COULD YIELD ADDITIONAL SNOW
SHOWERS AT ANY TIME. CONTINUED TO MAINTAIN THE PROB30 GROUP
DURING THE AFTERNOON FOR IFR VSBY FROM THE PREVIOUS TAF FOR
ORD/MDW/GYY/DPA GIVEN LOWER CONFIDENCE. CONFIDENCE IS ALSO LOWER
IN CIGS...AS THERE ARE POCKETS OF VFR OVER THE AREA. GUIDANCE IS
SHOWING A SIGNAL FOR INCREASED LOW-MID MVFR CIG POTENTIAL DURING
THE AFTERNOON AND POSSIBLY INTO THE EVENING. WINDS WILL BE WEST-
NORTHWEST...WITH GUSTS IN THE 20-25 KT RANGE THIS MORNING THROUGH
TONIGHT.

RC

&&

.MARINE...
258 AM CST

ISSUED A GALE WARNING FOR THE NORTHERN TWO THIRDS OF THE LAKE FROM
MID MORNING THROUGH EARLY WEDNESDAY MORNING. CONFIDENCE IS  JUST
HIGH ENOUGH TO ISSUE THE WARNING...BUT HAVE HIGH CONFIDENCE THAT ANY
GALES WILL BE ON THE LOW END OF THE SPECTRUM.  NO CHANGES WERE MADE
TO THE SMALL CRAFT ADVISORY WHICH GOES THROUGH THROUGH EARLY
WEDNESDAY NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY
MORNING FOR THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND
WAVES.

A WEAK LOW OVER LAKE ONTARIO REACHES NEW ENGLAND THIS EVENING...AND
THEN MERGES WITH A DEEPER LOW OVER THE ATLANTIC WEDNESDAY EVENING.
MEANWHILE HIGH PRESSURE OVER THE NORTHERN PLAINS WILL BUILD SOUTH
TIGHTENING THE PRESSURE GRADIENT OVER THE WESTERN GREAT LAKES.
NORTHWEST WINDS INCREASE TO LOW END GALES THIS MORNING AND PERSIST
INTO WEDNESDAY MORNING MAINLY ACROSS THE NORTHERN TWO THIRDS OF THE
LAKE.  OCCASIONAL GALES ARE POSSIBLE OVER THE SOUTHERN THIRD OF THE
LAKE TONIGHT INTO WEDNESDAY MORNING. DO NOT HAVE ENOUGH CONFIDENCE
IN A PROLONGED PERIOD OF GALE FORCE GUSTS TO HOIST A GALE WARNING
FOR THE SOUTHERN THIRD OF THE LAKE.

THE HIGH PASSES SOUTH OF THE LAKE THURSDAY EVENING AND WINDS WILL
BECOME WEST 15-25 KT.  A WEAK LOW FORMS OVER ONTARIO THURSDAY
EVENING AND REACHES NEW ENGLAND FRIDAY EVENING.  AT THE SAME TIME A
LARGE HIGH SPREADS OVER THE NORTHERN AND CENTRAL PLAINS. THIS WILL
LEAD TO NORTHWEST TO NORTH WINDS INCREASING TO AT LEAST 30 KT FRIDAY
AFTERNOON THROUGH SATURDAY MORNING.  THE HIGH MOVES OVER THE LAKE
SATURDAY EVENING AND CONTINUES EAST TO THE EASTERN GREAT LAKES
SUNDAY MORNING. WINDS BECOME SOUTH IN THE WAKE OF THE HIGH SUNDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 090859
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
259 AM CST TUE FEB 9 2016

.UPDATE...

742 PM CST

FOR EVENING UPDATE...

MINOR ADJUSTMENTS TO FORECAST THIS EVENING...TO REFINE TRANSITION
TO HIGHER POPS WITH SNOW SHOWERS SPREADING SOUTH ACROSS THE
NORTHEAST PORTION OF THE FORECAST AREA. ALSO...WITH SOME OF THE
HIGHER REFLECTIVITY RETURNS AND SOME BRIEF 1/2-3/4SM VISIBILITIES
REPORTED HAVE ALSO BUMPED UP QPF/SNOW AMOUNTS A BIT CLOSER TO AN
INCH THROUGH MIDNIGHT ESPECIALLY ACROSS PARTS OF LAKE/EASTERN
MCHENRY AND COOK COUNTIES THIS EVENING.

SNOW SHOWERS HAVE INCREASED IN COVERAGE ACROSS NORTHEAST IL...
SOUTHERN LAKE MICHIGAN AND FAR NORTHWEST INDIANA THIS EVENING IN
RESPONSE TO A SHEARED MID-LEVEL VORT MOVING SOUTH ACROSS LAKE
MICHIGAN. THIS IS EXPECTED TO CONTINUE OVERNIGHT...WITH FORECAST
SOUNDINGS DEPICTING COOLING OF THE SATURATED LAYER ESPECIALLY
BELOW 700 MB AND DEVELOPMENT OF A DEEP DENDRITIC GROWTH ZONE IN
EXCESS OF 200 MB. WHILE FORCING IS NOT TERRIBLY STRONG...THE
THERMODYNAMIC PROFILE SHOULD PRODUCE LIGHT SNOW FAIRLY EASILY.
LIGHT SNOW WAS ALSO SPREADING SOUTHEAST ACROSS THE UPPER
MISSISSIPPI VALLEY IN ASSOCIATION WITH A MID-LEVEL SPEED MAX
DROPPING INTO THE WESTERN PERIPHERY OF THE LARGE SCALE TROUGH OVER
EASTERN NORTH AMERICA...AND LIGHT SNOW SHOULD SPREAD INTO WESTERN
PARTS OF THE FA OVERNIGHT. THUS DESPITE RELATIVELY LOW QPF VALUES
ON THE ORDER OF A FEW HUNDREDTHS OF AN INCH IN ANY GIVEN PERIOD
HAVE CARRIED RELATIVELY HIGH POPS FOR LIGHT SNOW/SNOW SHOWERS INTO
TUESDAY.

OTHERWISE...FORECAST IN GOOD SHAPE WITH ONLY MINOR TWEAKS MADE PER
HOURLY OBS TRENDS EARLY THIS EVENING.

RATZER

&&

.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
300 PM CST

WEDNESDAY NIGHT THROUGH MONDAY...

BELOW NORMAL TEMPERATURES TO CONTINUE INTO THE WEEKEND AS LARGE
SCALE UPPER TROUGH OVER EASTERN NORTH AMERICA SHIFTS SLOWLY
EAST...BUT IS REINFORCED OVER THE WEEKEND BY ANOTHER CLOSED LOW
WHICH DEVELOPS OVER NEW ENGLAND/QUEBEC. EVENTUALLY THE TROUGH AXIS
SHIFTS FAR ENOUGH TO THE EAST FOR SOME MODERATION SUNDAY NIGHT
INTO MONDAY. STRONG NORTHWESTERLY FLOW ALOFT DOWNSTREAM OF
WESTERN/CENTRAL CONUS RIDGING WILL LIKELY SEE SEVERAL MINOR SHORT
WAVES RIPPLING THROUGH THE FLOW. DIFFERENCES REMAIN IN LONGER
RANGE GUIDANCE WITH LOCATION OF LOW LEVEL BAROCLINIC ZONE TO OUR
SOUTHWEST...THOUGH THE 00Z/12Z ECMWF HAVE MAINTAINED CONTINUITY IN
A MINOR DISTURBANCE TRACKING ACROSS THE MIDWEST FRIDAY WITH THE
POTENTIAL FOR SOME LIGHT SNOW. DEPENDING ON HOW QUICKLY HIGH
PRESSURE EXITS IN THE DAY 6-7 PERIOD THERE IS ALSO A CHANCE OF
LIGHT SNOW AS WARM ADVECTION DEVELOPS MONDAY. UNTIL THEN... COLD
IS THE RULE WITH OVERNIGHT LOWS IN THE SINGLE DIGITS (AND POSSIBLE
AROUND ZERO OR BELOW) AND HIGHS IN THE TEENS TO LOW 20S BEFORE
SLIGHT MODERATION TOWARD THE END OF THE FORECAST.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

LARGE UPPER LOW CENTERED WILL CONTINUE TO INFLUENCE AVIATION
WEATHER THROUGH TUESDAY EVENING. MAIN FORECAST CONCERN AND FOCUS
CONTINUES TO BE TIMING THE BEST WINDOW OF LOWER VSBY AND POTENTIAL
ACCUMULATIONS WITH OCCASIONAL SNOW SHOWERS. GYY AND MDW LOOKS TO
BE IN FAVORED CORRIDOR THROUGH THE EARLY MORNING HOURS/09-10Z...FOR
TEMPORARY IFR AND EVEN LIFR VSBY AT TIMES. FOR ORD/DPA...GENERALLY
MVFR VSBY IN SNOW SHOWERS DURING THIS TIME...ALTHOUGH CANNOT RULE
OUT IFR VSBY AT TIMES. SHORT RANGE GUIDANCE IS PICKING UP ON A
SUBTLE WAVE THAT COULD RE-ENHANCE SNOWFALL RATES TOWARD DAYBREAK.
AGAIN...GYY SHOULD BE MOST FAVORED...EVEN WITH SOME ADDED LAKE
ENHANCEMENT POTENTIAL. RFD AREA COULD FINALLY GET INTO SOME SNOW
SHOWER ACTIVITY AFTER 07Z...AND POTENTIALLY IFR VSBY AT TIMES.

THE REST OF THE DAY TUESDAY INTO TUESDAY EVENING...STEEP LOW
LEVEL LAPSE RATES AND WEAK LIFT COULD YIELD ADDITIONAL SNOW
SHOWERS AT ANY TIME. CONTINUED TO MAINTAIN THE PROB30 GROUP
DURING THE AFTERNOON FOR IFR VSBY FROM THE PREVIOUS TAF FOR
ORD/MDW/GYY/DPA GIVEN LOWER CONFIDENCE. CONFIDENCE IS ALSO LOWER
IN CIGS...AS THERE ARE POCKETS OF VFR OVER THE AREA. GUIDANCE IS
SHOWING A SIGNAL FOR INCREASED LOW-MID MVFR CIG POTENTIAL DURING
THE AFTERNOON AND POSSIBLY INTO THE EVENING. WINDS WILL BE WEST-
NORTHWEST...WITH GUSTS IN THE 20-25 KT RANGE THIS MORNING THROUGH
TONIGHT.

RC

&&

.MARINE...
258 AM CST

ISSUED A GALE WARNING FOR THE NORTHERN TWO THIRDS OF THE LAKE FROM
MID MORNING THROUGH EARLY WEDNESDAY MORNING. CONFIDENCE IS  JUST
HIGH ENOUGH TO ISSUE THE WARNING...BUT HAVE HIGH CONFIDENCE THAT ANY
GALES WILL BE ON THE LOW END OF THE SPECTRUM.  NO CHANGES WERE MADE
TO THE SMALL CRAFT ADVISORY WHICH GOES THROUGH THROUGH EARLY
WEDNESDAY NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY
MORNING FOR THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND
WAVES.

A WEAK LOW OVER LAKE ONTARIO REACHES NEW ENGLAND THIS EVENING...AND
THEN MERGES WITH A DEEPER LOW OVER THE ATLANTIC WEDNESDAY EVENING.
MEANWHILE HIGH PRESSURE OVER THE NORTHERN PLAINS WILL BUILD SOUTH
TIGHTENING THE PRESSURE GRADIENT OVER THE WESTERN GREAT LAKES.
NORTHWEST WINDS INCREASE TO LOW END GALES THIS MORNING AND PERSIST
INTO WEDNESDAY MORNING MAINLY ACROSS THE NORTHERN TWO THIRDS OF THE
LAKE.  OCCASIONAL GALES ARE POSSIBLE OVER THE SOUTHERN THIRD OF THE
LAKE TONIGHT INTO WEDNESDAY MORNING. DO NOT HAVE ENOUGH CONFIDENCE
IN A PROLONGED PERIOD OF GALE FORCE GUSTS TO HOIST A GALE WARNING
FOR THE SOUTHERN THIRD OF THE LAKE.

THE HIGH PASSES SOUTH OF THE LAKE THURSDAY EVENING AND WINDS WILL
BECOME WEST 15-25 KT.  A WEAK LOW FORMS OVER ONTARIO THURSDAY
EVENING AND REACHES NEW ENGLAND FRIDAY EVENING.  AT THE SAME TIME A
LARGE HIGH SPREADS OVER THE NORTHERN AND CENTRAL PLAINS. THIS WILL
LEAD TO NORTHWEST TO NORTH WINDS INCREASING TO AT LEAST 30 KT FRIDAY
AFTERNOON THROUGH SATURDAY MORNING.  THE HIGH MOVES OVER THE LAKE
SATURDAY EVENING AND CONTINUES EAST TO THE EASTERN GREAT LAKES
SUNDAY MORNING. WINDS BECOME SOUTH IN THE WAKE OF THE HIGH SUNDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 090859
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
259 AM CST TUE FEB 9 2016

.UPDATE...

742 PM CST

FOR EVENING UPDATE...

MINOR ADJUSTMENTS TO FORECAST THIS EVENING...TO REFINE TRANSITION
TO HIGHER POPS WITH SNOW SHOWERS SPREADING SOUTH ACROSS THE
NORTHEAST PORTION OF THE FORECAST AREA. ALSO...WITH SOME OF THE
HIGHER REFLECTIVITY RETURNS AND SOME BRIEF 1/2-3/4SM VISIBILITIES
REPORTED HAVE ALSO BUMPED UP QPF/SNOW AMOUNTS A BIT CLOSER TO AN
INCH THROUGH MIDNIGHT ESPECIALLY ACROSS PARTS OF LAKE/EASTERN
MCHENRY AND COOK COUNTIES THIS EVENING.

SNOW SHOWERS HAVE INCREASED IN COVERAGE ACROSS NORTHEAST IL...
SOUTHERN LAKE MICHIGAN AND FAR NORTHWEST INDIANA THIS EVENING IN
RESPONSE TO A SHEARED MID-LEVEL VORT MOVING SOUTH ACROSS LAKE
MICHIGAN. THIS IS EXPECTED TO CONTINUE OVERNIGHT...WITH FORECAST
SOUNDINGS DEPICTING COOLING OF THE SATURATED LAYER ESPECIALLY
BELOW 700 MB AND DEVELOPMENT OF A DEEP DENDRITIC GROWTH ZONE IN
EXCESS OF 200 MB. WHILE FORCING IS NOT TERRIBLY STRONG...THE
THERMODYNAMIC PROFILE SHOULD PRODUCE LIGHT SNOW FAIRLY EASILY.
LIGHT SNOW WAS ALSO SPREADING SOUTHEAST ACROSS THE UPPER
MISSISSIPPI VALLEY IN ASSOCIATION WITH A MID-LEVEL SPEED MAX
DROPPING INTO THE WESTERN PERIPHERY OF THE LARGE SCALE TROUGH OVER
EASTERN NORTH AMERICA...AND LIGHT SNOW SHOULD SPREAD INTO WESTERN
PARTS OF THE FA OVERNIGHT. THUS DESPITE RELATIVELY LOW QPF VALUES
ON THE ORDER OF A FEW HUNDREDTHS OF AN INCH IN ANY GIVEN PERIOD
HAVE CARRIED RELATIVELY HIGH POPS FOR LIGHT SNOW/SNOW SHOWERS INTO
TUESDAY.

OTHERWISE...FORECAST IN GOOD SHAPE WITH ONLY MINOR TWEAKS MADE PER
HOURLY OBS TRENDS EARLY THIS EVENING.

RATZER

&&

.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
300 PM CST

WEDNESDAY NIGHT THROUGH MONDAY...

BELOW NORMAL TEMPERATURES TO CONTINUE INTO THE WEEKEND AS LARGE
SCALE UPPER TROUGH OVER EASTERN NORTH AMERICA SHIFTS SLOWLY
EAST...BUT IS REINFORCED OVER THE WEEKEND BY ANOTHER CLOSED LOW
WHICH DEVELOPS OVER NEW ENGLAND/QUEBEC. EVENTUALLY THE TROUGH AXIS
SHIFTS FAR ENOUGH TO THE EAST FOR SOME MODERATION SUNDAY NIGHT
INTO MONDAY. STRONG NORTHWESTERLY FLOW ALOFT DOWNSTREAM OF
WESTERN/CENTRAL CONUS RIDGING WILL LIKELY SEE SEVERAL MINOR SHORT
WAVES RIPPLING THROUGH THE FLOW. DIFFERENCES REMAIN IN LONGER
RANGE GUIDANCE WITH LOCATION OF LOW LEVEL BAROCLINIC ZONE TO OUR
SOUTHWEST...THOUGH THE 00Z/12Z ECMWF HAVE MAINTAINED CONTINUITY IN
A MINOR DISTURBANCE TRACKING ACROSS THE MIDWEST FRIDAY WITH THE
POTENTIAL FOR SOME LIGHT SNOW. DEPENDING ON HOW QUICKLY HIGH
PRESSURE EXITS IN THE DAY 6-7 PERIOD THERE IS ALSO A CHANCE OF
LIGHT SNOW AS WARM ADVECTION DEVELOPS MONDAY. UNTIL THEN... COLD
IS THE RULE WITH OVERNIGHT LOWS IN THE SINGLE DIGITS (AND POSSIBLE
AROUND ZERO OR BELOW) AND HIGHS IN THE TEENS TO LOW 20S BEFORE
SLIGHT MODERATION TOWARD THE END OF THE FORECAST.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

LARGE UPPER LOW CENTERED WILL CONTINUE TO INFLUENCE AVIATION
WEATHER THROUGH TUESDAY EVENING. MAIN FORECAST CONCERN AND FOCUS
CONTINUES TO BE TIMING THE BEST WINDOW OF LOWER VSBY AND POTENTIAL
ACCUMULATIONS WITH OCCASIONAL SNOW SHOWERS. GYY AND MDW LOOKS TO
BE IN FAVORED CORRIDOR THROUGH THE EARLY MORNING HOURS/09-10Z...FOR
TEMPORARY IFR AND EVEN LIFR VSBY AT TIMES. FOR ORD/DPA...GENERALLY
MVFR VSBY IN SNOW SHOWERS DURING THIS TIME...ALTHOUGH CANNOT RULE
OUT IFR VSBY AT TIMES. SHORT RANGE GUIDANCE IS PICKING UP ON A
SUBTLE WAVE THAT COULD RE-ENHANCE SNOWFALL RATES TOWARD DAYBREAK.
AGAIN...GYY SHOULD BE MOST FAVORED...EVEN WITH SOME ADDED LAKE
ENHANCEMENT POTENTIAL. RFD AREA COULD FINALLY GET INTO SOME SNOW
SHOWER ACTIVITY AFTER 07Z...AND POTENTIALLY IFR VSBY AT TIMES.

THE REST OF THE DAY TUESDAY INTO TUESDAY EVENING...STEEP LOW
LEVEL LAPSE RATES AND WEAK LIFT COULD YIELD ADDITIONAL SNOW
SHOWERS AT ANY TIME. CONTINUED TO MAINTAIN THE PROB30 GROUP
DURING THE AFTERNOON FOR IFR VSBY FROM THE PREVIOUS TAF FOR
ORD/MDW/GYY/DPA GIVEN LOWER CONFIDENCE. CONFIDENCE IS ALSO LOWER
IN CIGS...AS THERE ARE POCKETS OF VFR OVER THE AREA. GUIDANCE IS
SHOWING A SIGNAL FOR INCREASED LOW-MID MVFR CIG POTENTIAL DURING
THE AFTERNOON AND POSSIBLY INTO THE EVENING. WINDS WILL BE WEST-
NORTHWEST...WITH GUSTS IN THE 20-25 KT RANGE THIS MORNING THROUGH
TONIGHT.

RC

&&

.MARINE...
258 AM CST

ISSUED A GALE WARNING FOR THE NORTHERN TWO THIRDS OF THE LAKE FROM
MID MORNING THROUGH EARLY WEDNESDAY MORNING. CONFIDENCE IS  JUST
HIGH ENOUGH TO ISSUE THE WARNING...BUT HAVE HIGH CONFIDENCE THAT ANY
GALES WILL BE ON THE LOW END OF THE SPECTRUM.  NO CHANGES WERE MADE
TO THE SMALL CRAFT ADVISORY WHICH GOES THROUGH THROUGH EARLY
WEDNESDAY NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY
MORNING FOR THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND
WAVES.

A WEAK LOW OVER LAKE ONTARIO REACHES NEW ENGLAND THIS EVENING...AND
THEN MERGES WITH A DEEPER LOW OVER THE ATLANTIC WEDNESDAY EVENING.
MEANWHILE HIGH PRESSURE OVER THE NORTHERN PLAINS WILL BUILD SOUTH
TIGHTENING THE PRESSURE GRADIENT OVER THE WESTERN GREAT LAKES.
NORTHWEST WINDS INCREASE TO LOW END GALES THIS MORNING AND PERSIST
INTO WEDNESDAY MORNING MAINLY ACROSS THE NORTHERN TWO THIRDS OF THE
LAKE.  OCCASIONAL GALES ARE POSSIBLE OVER THE SOUTHERN THIRD OF THE
LAKE TONIGHT INTO WEDNESDAY MORNING. DO NOT HAVE ENOUGH CONFIDENCE
IN A PROLONGED PERIOD OF GALE FORCE GUSTS TO HOIST A GALE WARNING
FOR THE SOUTHERN THIRD OF THE LAKE.

THE HIGH PASSES SOUTH OF THE LAKE THURSDAY EVENING AND WINDS WILL
BECOME WEST 15-25 KT.  A WEAK LOW FORMS OVER ONTARIO THURSDAY
EVENING AND REACHES NEW ENGLAND FRIDAY EVENING.  AT THE SAME TIME A
LARGE HIGH SPREADS OVER THE NORTHERN AND CENTRAL PLAINS. THIS WILL
LEAD TO NORTHWEST TO NORTH WINDS INCREASING TO AT LEAST 30 KT FRIDAY
AFTERNOON THROUGH SATURDAY MORNING.  THE HIGH MOVES OVER THE LAKE
SATURDAY EVENING AND CONTINUES EAST TO THE EASTERN GREAT LAKES
SUNDAY MORNING. WINDS BECOME SOUTH IN THE WAKE OF THE HIGH SUNDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 090534
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1134 PM CST MON FEB 8 2016

.UPDATE...

742 PM CST

FOR EVENING UPDATE...

MINOR ADJUSTMENTS TO FORECAST THIS EVENING...TO REFINE TRANSITION
TO HIGHER POPS WITH SNOW SHOWERS SPREADING SOUTH ACROSS THE
NORTHEAST PORTION OF THE FORECAST AREA. ALSO...WITH SOME OF THE
HIGHER REFLECTIVITY RETURNS AND SOME BRIEF 1/2-3/4SM VISIBILITIES
REPORTED HAVE ALSO BUMPED UP QPF/SNOW AMOUNTS A BIT CLOSER TO AN
INCH THROUGH MIDNIGHT ESPECIALLY ACROSS PARTS OF LAKE/EASTERN
MCHENRY AND COOK COUNTIES THIS EVENING.

SNOW SHOWERS HAVE INCREASED IN COVERAGE ACROSS NORTHEAST IL...
SOUTHERN LAKE MICHIGAN AND FAR NORTHWEST INDIANA THIS EVENING IN
RESPONSE TO A SHEARED MID-LEVEL VORT MOVING SOUTH ACROSS LAKE
MICHIGAN. THIS IS EXPECTED TO CONTINUE OVERNIGHT...WITH FORECAST
SOUNDINGS DEPICTING COOLING OF THE SATURATED LAYER ESPECIALLY
BELOW 700 MB AND DEVELOPMENT OF A DEEP DENDRITIC GROWTH ZONE IN
EXCESS OF 200 MB. WHILE FORCING IS NOT TERRIBLY STRONG...THE
THERMODYNAMIC PROFILE SHOULD PRODUCE LIGHT SNOW FAIRLY EASILY.
LIGHT SNOW WAS ALSO SPREADING SOUTHEAST ACROSS THE UPPER
MISSISSIPPI VALLEY IN ASSOCIATION WITH A MID-LEVEL SPEED MAX
DROPPING INTO THE WESTERN PERIPHERY OF THE LARGE SCALE TROUGH OVER
EASTERN NORTH AMERICA...AND LIGHT SNOW SHOULD SPREAD INTO WESTERN
PARTS OF THE FA OVERNIGHT. THUS DESPITE RELATIVELY LOW QPF VALUES
ON THE ORDER OF A FEW HUNDREDTHS OF AN INCH IN ANY GIVEN PERIOD
HAVE CARRIED RELATIVELY HIGH POPS FOR LIGHT SNOW/SNOW SHOWERS INTO
TUESDAY.

OTHERWISE...FORECAST IN GOOD SHAPE WITH ONLY MINOR TWEAKS MADE PER
HOURLY OBS TRENDS EARLY THIS EVENING.

RATZER

&&

.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
300 PM CST

WEDNESDAY NIGHT THROUGH MONDAY...

BELOW NORMAL TEMPERATURES TO CONTINUE INTO THE WEEKEND AS LARGE
SCALE UPPER TROUGH OVER EASTERN NORTH AMERICA SHIFTS SLOWLY
EAST...BUT IS REINFORCED OVER THE WEEKEND BY ANOTHER CLOSED LOW
WHICH DEVELOPS OVER NEW ENGLAND/QUEBEC. EVENTUALLY THE TROUGH AXIS
SHIFTS FAR ENOUGH TO THE EAST FOR SOME MODERATION SUNDAY NIGHT
INTO MONDAY. STRONG NORTHWESTERLY FLOW ALOFT DOWNSTREAM OF
WESTERN/CENTRAL CONUS RIDGING WILL LIKELY SEE SEVERAL MINOR SHORT
WAVES RIPPLING THROUGH THE FLOW. DIFFERENCES REMAIN IN LONGER
RANGE GUIDANCE WITH LOCATION OF LOW LEVEL BAROCLINIC ZONE TO OUR
SOUTHWEST...THOUGH THE 00Z/12Z ECMWF HAVE MAINTAINED CONTINUITY IN
A MINOR DISTURBANCE TRACKING ACROSS THE MIDWEST FRIDAY WITH THE
POTENTIAL FOR SOME LIGHT SNOW. DEPENDING ON HOW QUICKLY HIGH
PRESSURE EXITS IN THE DAY 6-7 PERIOD THERE IS ALSO A CHANCE OF
LIGHT SNOW AS WARM ADVECTION DEVELOPS MONDAY. UNTIL THEN... COLD
IS THE RULE WITH OVERNIGHT LOWS IN THE SINGLE DIGITS (AND POSSIBLE
AROUND ZERO OR BELOW) AND HIGHS IN THE TEENS TO LOW 20S BEFORE
SLIGHT MODERATION TOWARD THE END OF THE FORECAST.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

LARGE UPPER LOW CENTERED WILL CONTINUE TO INFLUENCE AVIATION
WEATHER THROUGH TUESDAY EVENING. MAIN FORECAST CONCERN AND FOCUS
CONTINUES TO BE TIMING THE BEST WINDOW OF LOWER VSBY AND POTENTIAL
ACCUMULATIONS WITH OCCASIONAL SNOW SHOWERS. GYY AND MDW LOOKS TO
BE IN FAVORED CORRIDOR THROUGH THE EARLY MORNING HOURS/09-10Z...FOR
TEMPORARY IFR AND EVEN LIFR VSBY AT TIMES. FOR ORD/DPA...GENERALLY
MVFR VSBY IN SNOW SHOWERS DURING THIS TIME...ALTHOUGH CANNOT RULE
OUT IFR VSBY AT TIMES. SHORT RANGE GUIDANCE IS PICKING UP ON A
SUBTLE WAVE THAT COULD RE-ENHANCE SNOWFALL RATES TOWARD DAYBREAK.
AGAIN...GYY SHOULD BE MOST FAVORED...EVEN WITH SOME ADDED LAKE
ENHANCEMENT POTENTIAL. RFD AREA COULD FINALLY GET INTO SOME SNOW
SHOWER ACTIVITY AFTER 07Z...AND POTENTIALLY IFR VSBY AT TIMES.

THE REST OF THE DAY TUESDAY INTO TUESDAY EVENING...STEEP LOW
LEVEL LAPSE RATES AND WEAK LIFT COULD YIELD ADDITIONAL SNOW
SHOWERS AT ANY TIME. CONTINUED TO MAINTAIN THE PROB30 GROUP
DURING THE AFTERNOON FOR IFR VSBY FROM THE PREVIOUS TAF FOR
ORD/MDW/GYY/DPA GIVEN LOWER CONFIDENCE. CONFIDENCE IS ALSO LOWER
IN CIGS...AS THERE ARE POCKETS OF VFR OVER THE AREA. GUIDANCE IS
SHOWING A SIGNAL FOR INCREASED LOW-MID MVFR CIG POTENTIAL DURING
THE AFTERNOON AND POSSIBLY INTO THE EVENING. WINDS WILL BE WEST-
NORTHWEST...WITH GUSTS IN THE 20-25 KT RANGE THIS MORNING THROUGH
TONIGHT.

RC

&&

.MARINE...
223 PM CST

LOW PRESSURE CENTERED NEAR LAKE HURON/LAKE ONTARIO EARLY THIS
AFTERNOON WILL VERY GRADUALLY MEANDER TOWARDS LAKE ONTARIO BY
TOMORROW NIGHT WITH MODERATELY STRONG NORTH TO NORTHWEST WINDS
EXPECTED TO BE IN PLACE ACROSS LAKE MICHIGAN. WINDS ARE EXPECTED
TO REMAIN AROUND 30 KT THIS EVENING THROUGH WEDNESDAY
NIGHT...WITH A FEW GALE FORCE GUSTS POSSIBLE MAINLY TUESDAY INTO
TUESDAY NIGHT. FREEZING SPRAY IS ALSO A CONCERN TUESDAY THROUGH
WEDNESDAY EVENING. HIGH PRESSURE WILL BUILD FROM THE UPPER
MIDWEST WEDNESDAY NIGHT INTO THE OHIO VALLEY THURSDAY NIGHT
RESULTING A MODEST TAPERING OF THE WINDS AS THEY BACK TO THE WEST.
ANOTHER COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN FRIDAY TURNING
WINDS BACK TO NORTHERLY AND PICKING UP ONCE AGAIN. THIS FRONT WILL
USHER IN A BITTERLY COLD ARCTIC AIRMASS WHICH COULD RESULT IN
ADDITIONAL GALES...PARTICULARLY FRIDAY NIGHT...AND FREEZING SPRAY
ACROSS LAKE MICHIGAN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 090534
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1134 PM CST MON FEB 8 2016

.UPDATE...

742 PM CST

FOR EVENING UPDATE...

MINOR ADJUSTMENTS TO FORECAST THIS EVENING...TO REFINE TRANSITION
TO HIGHER POPS WITH SNOW SHOWERS SPREADING SOUTH ACROSS THE
NORTHEAST PORTION OF THE FORECAST AREA. ALSO...WITH SOME OF THE
HIGHER REFLECTIVITY RETURNS AND SOME BRIEF 1/2-3/4SM VISIBILITIES
REPORTED HAVE ALSO BUMPED UP QPF/SNOW AMOUNTS A BIT CLOSER TO AN
INCH THROUGH MIDNIGHT ESPECIALLY ACROSS PARTS OF LAKE/EASTERN
MCHENRY AND COOK COUNTIES THIS EVENING.

SNOW SHOWERS HAVE INCREASED IN COVERAGE ACROSS NORTHEAST IL...
SOUTHERN LAKE MICHIGAN AND FAR NORTHWEST INDIANA THIS EVENING IN
RESPONSE TO A SHEARED MID-LEVEL VORT MOVING SOUTH ACROSS LAKE
MICHIGAN. THIS IS EXPECTED TO CONTINUE OVERNIGHT...WITH FORECAST
SOUNDINGS DEPICTING COOLING OF THE SATURATED LAYER ESPECIALLY
BELOW 700 MB AND DEVELOPMENT OF A DEEP DENDRITIC GROWTH ZONE IN
EXCESS OF 200 MB. WHILE FORCING IS NOT TERRIBLY STRONG...THE
THERMODYNAMIC PROFILE SHOULD PRODUCE LIGHT SNOW FAIRLY EASILY.
LIGHT SNOW WAS ALSO SPREADING SOUTHEAST ACROSS THE UPPER
MISSISSIPPI VALLEY IN ASSOCIATION WITH A MID-LEVEL SPEED MAX
DROPPING INTO THE WESTERN PERIPHERY OF THE LARGE SCALE TROUGH OVER
EASTERN NORTH AMERICA...AND LIGHT SNOW SHOULD SPREAD INTO WESTERN
PARTS OF THE FA OVERNIGHT. THUS DESPITE RELATIVELY LOW QPF VALUES
ON THE ORDER OF A FEW HUNDREDTHS OF AN INCH IN ANY GIVEN PERIOD
HAVE CARRIED RELATIVELY HIGH POPS FOR LIGHT SNOW/SNOW SHOWERS INTO
TUESDAY.

OTHERWISE...FORECAST IN GOOD SHAPE WITH ONLY MINOR TWEAKS MADE PER
HOURLY OBS TRENDS EARLY THIS EVENING.

RATZER

&&

.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
300 PM CST

WEDNESDAY NIGHT THROUGH MONDAY...

BELOW NORMAL TEMPERATURES TO CONTINUE INTO THE WEEKEND AS LARGE
SCALE UPPER TROUGH OVER EASTERN NORTH AMERICA SHIFTS SLOWLY
EAST...BUT IS REINFORCED OVER THE WEEKEND BY ANOTHER CLOSED LOW
WHICH DEVELOPS OVER NEW ENGLAND/QUEBEC. EVENTUALLY THE TROUGH AXIS
SHIFTS FAR ENOUGH TO THE EAST FOR SOME MODERATION SUNDAY NIGHT
INTO MONDAY. STRONG NORTHWESTERLY FLOW ALOFT DOWNSTREAM OF
WESTERN/CENTRAL CONUS RIDGING WILL LIKELY SEE SEVERAL MINOR SHORT
WAVES RIPPLING THROUGH THE FLOW. DIFFERENCES REMAIN IN LONGER
RANGE GUIDANCE WITH LOCATION OF LOW LEVEL BAROCLINIC ZONE TO OUR
SOUTHWEST...THOUGH THE 00Z/12Z ECMWF HAVE MAINTAINED CONTINUITY IN
A MINOR DISTURBANCE TRACKING ACROSS THE MIDWEST FRIDAY WITH THE
POTENTIAL FOR SOME LIGHT SNOW. DEPENDING ON HOW QUICKLY HIGH
PRESSURE EXITS IN THE DAY 6-7 PERIOD THERE IS ALSO A CHANCE OF
LIGHT SNOW AS WARM ADVECTION DEVELOPS MONDAY. UNTIL THEN... COLD
IS THE RULE WITH OVERNIGHT LOWS IN THE SINGLE DIGITS (AND POSSIBLE
AROUND ZERO OR BELOW) AND HIGHS IN THE TEENS TO LOW 20S BEFORE
SLIGHT MODERATION TOWARD THE END OF THE FORECAST.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

LARGE UPPER LOW CENTERED WILL CONTINUE TO INFLUENCE AVIATION
WEATHER THROUGH TUESDAY EVENING. MAIN FORECAST CONCERN AND FOCUS
CONTINUES TO BE TIMING THE BEST WINDOW OF LOWER VSBY AND POTENTIAL
ACCUMULATIONS WITH OCCASIONAL SNOW SHOWERS. GYY AND MDW LOOKS TO
BE IN FAVORED CORRIDOR THROUGH THE EARLY MORNING HOURS/09-10Z...FOR
TEMPORARY IFR AND EVEN LIFR VSBY AT TIMES. FOR ORD/DPA...GENERALLY
MVFR VSBY IN SNOW SHOWERS DURING THIS TIME...ALTHOUGH CANNOT RULE
OUT IFR VSBY AT TIMES. SHORT RANGE GUIDANCE IS PICKING UP ON A
SUBTLE WAVE THAT COULD RE-ENHANCE SNOWFALL RATES TOWARD DAYBREAK.
AGAIN...GYY SHOULD BE MOST FAVORED...EVEN WITH SOME ADDED LAKE
ENHANCEMENT POTENTIAL. RFD AREA COULD FINALLY GET INTO SOME SNOW
SHOWER ACTIVITY AFTER 07Z...AND POTENTIALLY IFR VSBY AT TIMES.

THE REST OF THE DAY TUESDAY INTO TUESDAY EVENING...STEEP LOW
LEVEL LAPSE RATES AND WEAK LIFT COULD YIELD ADDITIONAL SNOW
SHOWERS AT ANY TIME. CONTINUED TO MAINTAIN THE PROB30 GROUP
DURING THE AFTERNOON FOR IFR VSBY FROM THE PREVIOUS TAF FOR
ORD/MDW/GYY/DPA GIVEN LOWER CONFIDENCE. CONFIDENCE IS ALSO LOWER
IN CIGS...AS THERE ARE POCKETS OF VFR OVER THE AREA. GUIDANCE IS
SHOWING A SIGNAL FOR INCREASED LOW-MID MVFR CIG POTENTIAL DURING
THE AFTERNOON AND POSSIBLY INTO THE EVENING. WINDS WILL BE WEST-
NORTHWEST...WITH GUSTS IN THE 20-25 KT RANGE THIS MORNING THROUGH
TONIGHT.

RC

&&

.MARINE...
223 PM CST

LOW PRESSURE CENTERED NEAR LAKE HURON/LAKE ONTARIO EARLY THIS
AFTERNOON WILL VERY GRADUALLY MEANDER TOWARDS LAKE ONTARIO BY
TOMORROW NIGHT WITH MODERATELY STRONG NORTH TO NORTHWEST WINDS
EXPECTED TO BE IN PLACE ACROSS LAKE MICHIGAN. WINDS ARE EXPECTED
TO REMAIN AROUND 30 KT THIS EVENING THROUGH WEDNESDAY
NIGHT...WITH A FEW GALE FORCE GUSTS POSSIBLE MAINLY TUESDAY INTO
TUESDAY NIGHT. FREEZING SPRAY IS ALSO A CONCERN TUESDAY THROUGH
WEDNESDAY EVENING. HIGH PRESSURE WILL BUILD FROM THE UPPER
MIDWEST WEDNESDAY NIGHT INTO THE OHIO VALLEY THURSDAY NIGHT
RESULTING A MODEST TAPERING OF THE WINDS AS THEY BACK TO THE WEST.
ANOTHER COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN FRIDAY TURNING
WINDS BACK TO NORTHERLY AND PICKING UP ONCE AGAIN. THIS FRONT WILL
USHER IN A BITTERLY COLD ARCTIC AIRMASS WHICH COULD RESULT IN
ADDITIONAL GALES...PARTICULARLY FRIDAY NIGHT...AND FREEZING SPRAY
ACROSS LAKE MICHIGAN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 3 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 090142
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
742 PM CST MON FEB 8 2016

.UPDATE...
742 PM CST

FOR EVENING UPDATE...

MINOR ADJUSTMENTS TO FORECAST THIS EVENING...TO REFINE TRANSITION
TO HIGHER POPS WITH SNOW SHOWERS SPREADING SOUTH ACROSS THE
NORTHEAST PORTION OF THE FORECAST AREA. ALSO...WITH SOME OF THE
HIGHER REFLECTIVITY RETURNS AND SOME BRIEF 1/2-3/4SM VISIBILITIES
REPORTED HAVE ALSO BUMPED UP QPF/SNOW AMOUNTS A BIT CLOSER TO AN
INCH THROUGH MIDNIGHT ESPECIALLY ACROSS PARTS OF LAKE/EASTERN
MCHENRY AND COOK COUNTIES THIS EVENING.

SNOW SHOWERS HAVE INCREASED IN COVERAGE ACROSS NORTHEAST IL...
SOUTHERN LAKE MICHIGAN AND FAR NORTHWEST INDIANA THIS EVENING IN
RESPONSE TO A SHEARED MID-LEVEL VORT MOVING SOUTH ACROSS LAKE
MICHIGAN. THIS IS EXPECTED TO CONTINUE OVERNIGHT...WITH FORECAST
SOUNDINGS DEPICTING COOLING OF THE SATURATED LAYER ESPECIALLY
BELOW 700 MB AND DEVELOPMENT OF A DEEP DENDRITIC GROWTH ZONE IN
EXCESS OF 200 MB. WHILE FORCING IS NOT TERRIBLY STRONG...THE
THERMODYNAMIC PROFILE SHOULD PRODUCE LIGHT SNOW FAIRLY EASILY.
LIGHT SNOW WAS ALSO SPREADING SOUTHEAST ACROSS THE UPPER
MISSISSIPPI VALLEY IN ASSOCIATION WITH A MID-LEVEL SPEED MAX
DROPPING INTO THE WESTERN PERIPHERY OF THE LARGE SCALE TROUGH OVER
EASTERN NORTH AMERICA...AND LIGHT SNOW SHOULD SPREAD INTO WESTERN
PARTS OF THE FA OVERNIGHT. THUS DESPITE RELATIVELY LOW QPF VALUES
ON THE ORDER OF A FEW HUNDREDTHS OF AN INCH IN ANY GIVEN PERIOD
HAVE CARRIED RELATIVELY HIGH POPS FOR LIGHT SNOW/SNOW SHOWERS INTO
TUESDAY.

OTHERWISE...FORECAST IN GOOD SHAPE WITH ONLY MINOR TWEAKS MADE PER
HOURLY OBS TRENDS EARLY THIS EVENING.

RATZER

&&

.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
300 PM CST

WEDNESDAY NIGHT THROUGH MONDAY...

BELOW NORMAL TEMPERATURES TO CONTINUE INTO THE WEEKEND AS LARGE
SCALE UPPER TROUGH OVER EASTERN NORTH AMERICA SHIFTS SLOWLY
EAST...BUT IS REINFORCED OVER THE WEEKEND BY ANOTHER CLOSED LOW
WHICH DEVELOPS OVER NEW ENGLAND/QUEBEC. EVENTUALLY THE TROUGH AXIS
SHIFTS FAR ENOUGH TO THE EAST FOR SOME MODERATION SUNDAY NIGHT
INTO MONDAY. STRONG NORTHWESTERLY FLOW ALOFT DOWNSTREAM OF
WESTERN/CENTRAL CONUS RIDGING WILL LIKELY SEE SEVERAL MINOR SHORT
WAVES RIPPLING THROUGH THE FLOW. DIFFERENCES REMAIN IN LONGER
RANGE GUIDANCE WITH LOCATION OF LOW LEVEL BAROCLINIC ZONE TO OUR
SOUTHWEST...THOUGH THE 00Z/12Z ECMWF HAVE MAINTAINED CONTINUITY IN
A MINOR DISTURBANCE TRACKING ACROSS THE MIDWEST FRIDAY WITH THE
POTENTIAL FOR SOME LIGHT SNOW. DEPENDING ON HOW QUICKLY HIGH
PRESSURE EXITS IN THE DAY 6-7 PERIOD THERE IS ALSO A CHANCE OF
LIGHT SNOW AS WARM ADVECTION DEVELOPS MONDAY. UNTIL THEN... COLD
IS THE RULE WITH OVERNIGHT LOWS IN THE SINGLE DIGITS (AND POSSIBLE
AROUND ZERO OR BELOW) AND HIGHS IN THE TEENS TO LOW 20S BEFORE
SLIGHT MODERATION TOWARD THE END OF THE FORECAST.

RATZER

&&

.AVIATION...
FOR THE 00Z TAFS...

LARGE UPPER LOW CENTERED NEAR LAKE MICHIGAN THIS EVENING WILL
CONTINUE TO INFLUENCE AVIATION WEATHER THROUGH TUESDAY. MAIN
FORECAST CONCERN AND FOCUS IS TIMING THE BEST WINDOW OF LOWER
VSBY AND POTENTIAL ACCUMULATIONS WITH OCCASIONAL SNOW SHOWERS. A
FAIRLY INTENSE SNOW SHOWER IS APPROACHING ORD THIS HOUR AND DID
DROP PWK DOWN TO 1/2 SM VSBY BRIEFLY. FURTHER UPSTREAM...MKE ALSO
BRIEFLY DROPPED TO 1/2 SM VSBY. THE MAIN FOCUS THIS EVENING WILL
BE WITH MORE CONCENTRATED AREA OF SNOW SHOWERS OVER EASTERN
WISCONSIN AND LAKE MICHIGAN THAT WILL DRIFT SOUTH OVER NORTHEAST
ILLINOIS AND NORTHWEST INDIANA. MOVED UP TIMING OF TEMPO FOR IFR
VSBY TO THE EVENING HOURS...BUT COULD POTENTIALLY NEED ANOTHER
TEMPO AFTER MIDNIGHT. MORE INTENSE SNOW SHOWERS DO HAVE THE
POTENTIAL TO PRODUCE LIFR VSBY AS SEEN AT PWK AND MKE RECENTLY.
LOOKING AT UP GENERALLY UP TO 1 INCH ACCUMULATION BY DAYBREAK
TUESDAY...THOUGH HIGHER AMOUNTS ARE POSSIBLE UNDER PERSISTENT
HEAVIER SNOW SHOWERS. RFD AREA LOOKS TO BE ON THE WESTERN FRINGE
OF THE EVENING ACTIVITY...WITH THE SNOW SHOWER ACTIVITY OFF TO THE
NORTHWEST EXPECTED TO ARRIVE OVERNIGHT/06Z AND LATER.

THE REST OF THE DAY TUESDAY INTO TUESDAY EVENING...STEEP LOW
LEVEL LAPSE RATES AND WEAK LIFT COULD YIELD ADDITIONAL SNOW
SHOWERS AT ANY TIME. DID NOT MAKE A SIGNIFICANT CHANGE TO THE
PROB30 GROUP DURING THE AFTERNOON FROM THE PREVIOUS ORD TAF AND
INCLUDED IT WITH THE REMAINING EASTERN TAF SITES FOR THE 00Z
ISSUANCE. CIGS SHOULD GENERALLY BE MVFR THROUGH THE PERIOD...WITH
WEST-NORTHWEST WINDS GUSTING TO 20-25 KT THIS EVENING THROUGH
TUESDAY EVENING.

RC

&&

.MARINE...
223 PM CST

LOW PRESSURE CENTERED NEAR LAKE HURON/LAKE ONTARIO EARLY THIS
AFTERNOON WILL VERY GRADUALLY MEANDER TOWARDS LAKE ONTARIO BY
TOMORROW NIGHT WITH MODERATELY STRONG NORTH TO NORTHWEST WINDS
EXPECTED TO BE IN PLACE ACROSS LAKE MICHIGAN. WINDS ARE EXPECTED
TO REMAIN AROUND 30 KT THIS EVENING THROUGH WEDNESDAY
NIGHT...WITH A FEW GALE FORCE GUSTS POSSIBLE MAINLY TUESDAY INTO
TUESDAY NIGHT. FREEZING SPRAY IS ALSO A CONCERN TUESDAY THROUGH
WEDNESDAY EVENING. HIGH PRESSURE WILL BUILD FROM THE UPPER
MIDWEST WEDNESDAY NIGHT INTO THE OHIO VALLEY THURSDAY NIGHT
RESULTING A MODEST TAPERING OF THE WINDS AS THEY BACK TO THE WEST.
ANOTHER COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN FRIDAY TURNING
WINDS BACK TO NORTHERLY AND PICKING UP ONCE AGAIN. THIS FRONT WILL
USHER IN A BITTERLY COLD ARCTIC AIRMASS WHICH COULD RESULT IN
ADDITIONAL GALES...PARTICULARLY FRIDAY NIGHT...AND FREEZING SPRAY
ACROSS LAKE MICHIGAN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 090017
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
617 PM CST MON FEB 8 2016

.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
300 PM CST

WEDNESDAY NIGHT THROUGH MONDAY...

BELOW NORMAL TEMPERATURES TO CONTINUE INTO THE WEEKEND AS LARGE
SCALE UPPER TROUGH OVER EASTERN NORTH AMERICA SHIFTS SLOWLY
EAST...BUT IS REINFORCED OVER THE WEEKEND BY ANOTHER CLOSED LOW
WHICH DEVELOPS OVER NEW ENGLAND/QUEBEC. EVENTUALLY THE TROUGH AXIS
SHIFTS FAR ENOUGH TO THE EAST FOR SOME MODERATION SUNDAY NIGHT
INTO MONDAY. STRONG NORTHWESTERLY FLOW ALOFT DOWNSTREAM OF
WESTERN/CENTRAL CONUS RIDGING WILL LIKELY SEE SEVERAL MINOR SHORT
WAVES RIPPLING THROUGH THE FLOW. DIFFERENCES REMAIN IN LONGER
RANGE GUIDANCE WITH LOCATION OF LOW LEVEL BAROCLINIC ZONE TO OUR
SOUTHWEST...THOUGH THE 00Z/12Z ECMWF HAVE MAINTAINED CONTINUITY IN
A MINOR DISTURBANCE TRACKING ACROSS THE MIDWEST FRIDAY WITH THE
POTENTIAL FOR SOME LIGHT SNOW. DEPENDING ON HOW QUICKLY HIGH
PRESSURE EXITS IN THE DAY 6-7 PERIOD THERE IS ALSO A CHANCE OF
LIGHT SNOW AS WARM ADVECTION DEVELOPS MONDAY. UNTIL THEN... COLD
IS THE RULE WITH OVERNIGHT LOWS IN THE SINGLE DIGITS (AND POSSIBLE
AROUND ZERO OR BELOW) AND HIGHS IN THE TEENS TO LOW 20S BEFORE
SLIGHT MODERATION TOWARD THE END OF THE FORECAST.

RATZER

&&

.AVIATION...
FOR THE 00Z TAFS...

LARGE UPPER LOW CENTERED NEAR LAKE MICHIGAN THIS EVENING WILL
CONTINUE TO INFLUENCE AVIATION WEATHER THROUGH TUESDAY. MAIN
FORECAST CONCERN AND FOCUS IS TIMING THE BEST WINDOW OF LOWER
VSBY AND POTENTIAL ACCUMULATIONS WITH OCCASIONAL SNOW SHOWERS. A
FAIRLY INTENSE SNOW SHOWER IS APPROACHING ORD THIS HOUR AND DID
DROP PWK DOWN TO 1/2 SM VSBY BRIEFLY. FURTHER UPSTREAM...MKE ALSO
BRIEFLY DROPPED TO 1/2 SM VSBY. THE MAIN FOCUS THIS EVENING WILL
BE WITH MORE CONCENTRATED AREA OF SNOW SHOWERS OVER EASTERN
WISCONSIN AND LAKE MICHIGAN THAT WILL DRIFT SOUTH OVER NORTHEAST
ILLINOIS AND NORTHWEST INDIANA. MOVED UP TIMING OF TEMPO FOR IFR
VSBY TO THE EVENING HOURS...BUT COULD POTENTIALLY NEED ANOTHER
TEMPO AFTER MIDNIGHT. MORE INTENSE SNOW SHOWERS DO HAVE THE
POTENTIAL TO PRODUCE LIFR VSBY AS SEEN AT PWK AND MKE RECENTLY.
LOOKING AT UP GENERALLY UP TO 1 INCH ACCUMULATION BY DAYBREAK
TUESDAY...THOUGH HIGHER AMOUNTS ARE POSSIBLE UNDER PERSISTENT
HEAVIER SNOW SHOWERS. RFD AREA LOOKS TO BE ON THE WESTERN FRINGE
OF THE EVENING ACTIVITY...WITH THE SNOW SHOWER ACTIVITY OFF TO THE
NORTHWEST EXPECTED TO ARRIVE OVERNIGHT/06Z AND LATER.

THE REST OF THE DAY TUESDAY INTO TUESDAY EVENING...STEEP LOW
LEVEL LAPSE RATES AND WEAK LIFT COULD YIELD ADDITIONAL SNOW
SHOWERS AT ANY TIME. DID NOT MAKE A SIGNIFICANT CHANGE TO THE
PROB30 GROUP DURING THE AFTERNOON FROM THE PREVIOUS ORD TAF AND
INCLUDED IT WITH THE REMAINING EASTERN TAF SITES FOR THE 00Z
ISSUANCE. CIGS SHOULD GENERALLY BE MVFR THROUGH THE PERIOD...WITH
WEST-NORTHWEST WINDS GUSTING TO 20-25 KT THIS EVENING THROUGH
TUESDAY EVENING.

RC

&&

.MARINE...
223 PM CST

LOW PRESSURE CENTERED NEAR LAKE HURON/LAKE ONTARIO EARLY THIS
AFTERNOON WILL VERY GRADUALLY MEANDER TOWARDS LAKE ONTARIO BY
TOMORROW NIGHT WITH MODERATELY STRONG NORTH TO NORTHWEST WINDS
EXPECTED TO BE IN PLACE ACROSS LAKE MICHIGAN. WINDS ARE EXPECTED
TO REMAIN AROUND 30 KT THIS EVENING THROUGH WEDNESDAY
NIGHT...WITH A FEW GALE FORCE GUSTS POSSIBLE MAINLY TUESDAY INTO
TUESDAY NIGHT. FREEZING SPRAY IS ALSO A CONCERN TUESDAY THROUGH
WEDNESDAY EVENING. HIGH PRESSURE WILL BUILD FROM THE UPPER
MIDWEST WEDNESDAY NIGHT INTO THE OHIO VALLEY THURSDAY NIGHT
RESULTING A MODEST TAPERING OF THE WINDS AS THEY BACK TO THE WEST.
ANOTHER COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN FRIDAY TURNING
WINDS BACK TO NORTHERLY AND PICKING UP ONCE AGAIN. THIS FRONT WILL
USHER IN A BITTERLY COLD ARCTIC AIRMASS WHICH COULD RESULT IN
ADDITIONAL GALES...PARTICULARLY FRIDAY NIGHT...AND FREEZING SPRAY
ACROSS LAKE MICHIGAN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 090017
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
617 PM CST MON FEB 8 2016

.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
300 PM CST

WEDNESDAY NIGHT THROUGH MONDAY...

BELOW NORMAL TEMPERATURES TO CONTINUE INTO THE WEEKEND AS LARGE
SCALE UPPER TROUGH OVER EASTERN NORTH AMERICA SHIFTS SLOWLY
EAST...BUT IS REINFORCED OVER THE WEEKEND BY ANOTHER CLOSED LOW
WHICH DEVELOPS OVER NEW ENGLAND/QUEBEC. EVENTUALLY THE TROUGH AXIS
SHIFTS FAR ENOUGH TO THE EAST FOR SOME MODERATION SUNDAY NIGHT
INTO MONDAY. STRONG NORTHWESTERLY FLOW ALOFT DOWNSTREAM OF
WESTERN/CENTRAL CONUS RIDGING WILL LIKELY SEE SEVERAL MINOR SHORT
WAVES RIPPLING THROUGH THE FLOW. DIFFERENCES REMAIN IN LONGER
RANGE GUIDANCE WITH LOCATION OF LOW LEVEL BAROCLINIC ZONE TO OUR
SOUTHWEST...THOUGH THE 00Z/12Z ECMWF HAVE MAINTAINED CONTINUITY IN
A MINOR DISTURBANCE TRACKING ACROSS THE MIDWEST FRIDAY WITH THE
POTENTIAL FOR SOME LIGHT SNOW. DEPENDING ON HOW QUICKLY HIGH
PRESSURE EXITS IN THE DAY 6-7 PERIOD THERE IS ALSO A CHANCE OF
LIGHT SNOW AS WARM ADVECTION DEVELOPS MONDAY. UNTIL THEN... COLD
IS THE RULE WITH OVERNIGHT LOWS IN THE SINGLE DIGITS (AND POSSIBLE
AROUND ZERO OR BELOW) AND HIGHS IN THE TEENS TO LOW 20S BEFORE
SLIGHT MODERATION TOWARD THE END OF THE FORECAST.

RATZER

&&

.AVIATION...
FOR THE 00Z TAFS...

LARGE UPPER LOW CENTERED NEAR LAKE MICHIGAN THIS EVENING WILL
CONTINUE TO INFLUENCE AVIATION WEATHER THROUGH TUESDAY. MAIN
FORECAST CONCERN AND FOCUS IS TIMING THE BEST WINDOW OF LOWER
VSBY AND POTENTIAL ACCUMULATIONS WITH OCCASIONAL SNOW SHOWERS. A
FAIRLY INTENSE SNOW SHOWER IS APPROACHING ORD THIS HOUR AND DID
DROP PWK DOWN TO 1/2 SM VSBY BRIEFLY. FURTHER UPSTREAM...MKE ALSO
BRIEFLY DROPPED TO 1/2 SM VSBY. THE MAIN FOCUS THIS EVENING WILL
BE WITH MORE CONCENTRATED AREA OF SNOW SHOWERS OVER EASTERN
WISCONSIN AND LAKE MICHIGAN THAT WILL DRIFT SOUTH OVER NORTHEAST
ILLINOIS AND NORTHWEST INDIANA. MOVED UP TIMING OF TEMPO FOR IFR
VSBY TO THE EVENING HOURS...BUT COULD POTENTIALLY NEED ANOTHER
TEMPO AFTER MIDNIGHT. MORE INTENSE SNOW SHOWERS DO HAVE THE
POTENTIAL TO PRODUCE LIFR VSBY AS SEEN AT PWK AND MKE RECENTLY.
LOOKING AT UP GENERALLY UP TO 1 INCH ACCUMULATION BY DAYBREAK
TUESDAY...THOUGH HIGHER AMOUNTS ARE POSSIBLE UNDER PERSISTENT
HEAVIER SNOW SHOWERS. RFD AREA LOOKS TO BE ON THE WESTERN FRINGE
OF THE EVENING ACTIVITY...WITH THE SNOW SHOWER ACTIVITY OFF TO THE
NORTHWEST EXPECTED TO ARRIVE OVERNIGHT/06Z AND LATER.

THE REST OF THE DAY TUESDAY INTO TUESDAY EVENING...STEEP LOW
LEVEL LAPSE RATES AND WEAK LIFT COULD YIELD ADDITIONAL SNOW
SHOWERS AT ANY TIME. DID NOT MAKE A SIGNIFICANT CHANGE TO THE
PROB30 GROUP DURING THE AFTERNOON FROM THE PREVIOUS ORD TAF AND
INCLUDED IT WITH THE REMAINING EASTERN TAF SITES FOR THE 00Z
ISSUANCE. CIGS SHOULD GENERALLY BE MVFR THROUGH THE PERIOD...WITH
WEST-NORTHWEST WINDS GUSTING TO 20-25 KT THIS EVENING THROUGH
TUESDAY EVENING.

RC

&&

.MARINE...
223 PM CST

LOW PRESSURE CENTERED NEAR LAKE HURON/LAKE ONTARIO EARLY THIS
AFTERNOON WILL VERY GRADUALLY MEANDER TOWARDS LAKE ONTARIO BY
TOMORROW NIGHT WITH MODERATELY STRONG NORTH TO NORTHWEST WINDS
EXPECTED TO BE IN PLACE ACROSS LAKE MICHIGAN. WINDS ARE EXPECTED
TO REMAIN AROUND 30 KT THIS EVENING THROUGH WEDNESDAY
NIGHT...WITH A FEW GALE FORCE GUSTS POSSIBLE MAINLY TUESDAY INTO
TUESDAY NIGHT. FREEZING SPRAY IS ALSO A CONCERN TUESDAY THROUGH
WEDNESDAY EVENING. HIGH PRESSURE WILL BUILD FROM THE UPPER
MIDWEST WEDNESDAY NIGHT INTO THE OHIO VALLEY THURSDAY NIGHT
RESULTING A MODEST TAPERING OF THE WINDS AS THEY BACK TO THE WEST.
ANOTHER COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN FRIDAY TURNING
WINDS BACK TO NORTHERLY AND PICKING UP ONCE AGAIN. THIS FRONT WILL
USHER IN A BITTERLY COLD ARCTIC AIRMASS WHICH COULD RESULT IN
ADDITIONAL GALES...PARTICULARLY FRIDAY NIGHT...AND FREEZING SPRAY
ACROSS LAKE MICHIGAN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 082101
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
301 PM CST MON FEB 8 2016

.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
300 PM CST

WEDNESDAY NIGHT THROUGH MONDAY...

BELOW NORMAL TEMPERATURES TO CONTINUE INTO THE WEEKEND AS LARGE
SCALE UPPER TROUGH OVER EASTERN NORTH AMERICA SHIFTS SLOWLY
EAST...BUT IS REINFORCED OVER THE WEEKEND BY ANOTHER CLOSED LOW
WHICH DEVELOPS OVER NEW ENGLAND/QUEBEC. EVENTUALLY THE TROUGH AXIS
SHIFTS FAR ENOUGH TO THE EAST FOR SOME MODERATION SUNDAY NIGHT
INTO MONDAY. STRONG NORTHWESTERLY FLOW ALOFT DOWNSTREAM OF
WESTERN/CENTRAL CONUS RIDGING WILL LIKELY SEE SEVERAL MINOR SHORT
WAVES RIPPLING THROUGH THE FLOW. DIFFERENCES REMAIN IN LONGER
RANGE GUIDANCE WITH LOCATION OF LOW LEVEL BAROCLINIC ZONE TO OUR
SOUTHWEST...THOUGH THE 00Z/12Z ECMWF HAVE MAINTAINED CONTINUITY IN
A MINOR DISTURBANCE TRACKING ACROSS THE MIDWEST FRIDAY WITH THE
POTENTIAL FOR SOME LIGHT SNOW. DEPENDING ON HOW QUICKLY HIGH
PRESSURE EXITS IN THE DAY 6-7 PERIOD THERE IS ALSO A CHANCE OF
LIGHT SNOW AS WARM ADVECTION DEVELOPS MONDAY. UNTIL THEN... COLD
IS THE RULE WITH OVERNIGHT LOWS IN THE SINGLE DIGITS (AND POSSIBLE
AROUND ZERO OR BELOW) AND HIGHS IN THE TEENS TO LOW 20S BEFORE
SLIGHT MODERATION TOWARD THE END OF THE FORECAST.

RATZER

&&

.AVIATION...
FOR THE 18Z TAFS...

UPPER LEVEL LOW OVER LAKE MICHIGAN EARLY THIS AFTERNOON WILL
CONTINUE TO SLOWLY MEANDER EASTWARD ACROSS THE GREAT LAKES TODAY
AND TOMORROW WITH PINWHEELING UPPER LEVEL DISTURBANCES BRINGING
PERIODIC CHANCES FOR LIGHT SNOW SHOWERS AND FLURRIES TO THE
REGION. ONE OF THESE WAVES IS NOW DROPPING SOUTH INTO CENTRAL
ILLINOIS WHICH SHOULD ALLOW A LULL IN THE SNOW ACTIVITY IN ITS
WAKE THROUGH THE REST OF THE AFTERNOON. ANOTHER WAVE IS PROGGED TO
ROTATE ACROSS THE TERMINALS LATE THIS EVENING AND TONIGHT. FORCING
IS FAIRLY WEAK HOWEVER LOW LEVEL MOISTURE IS FOCUSED WITHIN A
RELATIVELY DEEP SNOW GROWTH ZONE WHICH SHOULD ALLOW FOR EFFICIENT
SNOW PRODUCTION. CONFIDENCE IN THE TIMING DETAILS REMAINS FAIRLY
LOW THOUGH GIVEN THE RATHER BENIGN FORCING. DURING THE DAY
TUESDAY...COLD AIR SPILLING INTO THE REGION WILL RESULT IN
STEEPENING LOW LEVEL LAPSE RATES AND ONCE AGAIN PRIME THE
ATMOSPHERE FOR DECENT SNOW PRODUCTION IF WE REALIZE ANY
FORCING...HOWEVER ANY FORCING CONTINUES TO BE WEAK RESULTING IN
CONSIDERABLE UNCERTAINTY SO FOR NOW WILL JUST INTRODUCE A PROB30
FOR SNOW EARLY TO MID AFTERNOON. WINDS WILL REMAIN OUT OF THE
NORTHWEST THROUGH THE PERIOD...WITH GUSTS INCREASING LATE THIS
AFTERNOON INTO EARLY EVENING. EXPECT CIGS TO REMAIN MVFR THROUGH
THE PERIOD.

BMD

&&

.MARINE...
223 PM CST

LOW PRESSURE CENTERED NEAR LAKE HURON/LAKE ONTARIO EARLY THIS
AFTERNOON WILL VERY GRADUALLY MEANDER TOWARDS LAKE ONTARIO BY
TOMORROW NIGHT WITH MODERATELY STRONG NORTH TO NORTHWEST WINDS
EXPECTED TO BE IN PLACE ACROSS LAKE MICHIGAN. WINDS ARE EXPECTED
TO REMAIN AROUND 30 KT THIS EVENING THROUGH WEDNESDAY
NIGHT...WITH A FEW GALE FORCE GUSTS POSSIBLE MAINLY TUESDAY INTO
TUESDAY NIGHT. FREEZING SPRAY IS ALSO A CONCERN TUESDAY THROUGH
WEDNESDAY EVENING. HIGH PRESSURE WILL BUILD FROM THE UPPER
MIDWEST WEDNESDAY NIGHT INTO THE OHIO VALLEY THURSDAY NIGHT
RESULTING A MODEST TAPERING OF THE WINDS AS THEY BACK TO THE WEST.
ANOTHER COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN FRIDAY TURNING
WINDS BACK TO NORTHERLY AND PICKING UP ONCE AGAIN. THIS FRONT WILL
USHER IN A BITTERLY COLD ARCTIC AIRMASS WHICH COULD RESULT IN
ADDITIONAL GALES...PARTICULARLY FRIDAY NIGHT...AND FREEZING SPRAY
ACROSS LAKE MICHIGAN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 082050
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CST MON FEB 8 2016


.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
340 AM CST

WEDNESDAY NIGHT THROUGH MONDAY...

THE PATTERN CONTINUES TO LOOK LIKE A COOLER THAN NORMAL ONE IN
THIS TIME PERIOD. THE ELEVATED BAROCLINIC ZONE ON THE WESTERN SIDE
OF THE EASTERN NORTH AMERICAN TROUGH LOOKS TO BE UNSETTLED WITH
SEVERAL RIPPLES SUPPORTING OCCASIONAL LIGHT SNOW
CHANCES...ALTHOUGH THE PLACEMENT OF THAT HAS LARGE SPREAD IN
GUIDANCE AT THIS TIME. AN EVEN MORE ANOMALOUS UPPER LEVEL LOW IS
FORECAST TO DIG INTO EASTERN CANADA BY FRIDAY OR SATURDAY...WITH
THE EC FURTHER SOUTH WITH THIS FEATURE. THIS RESULTS IN SOME
DIFFERENCES IN THE SURFACE PRESSURE FIELDS BETWEEN THE GFS AND
EC...THOUGH THE GENERAL SYNOPTIC PATTERN WITH A STRONG CANADIAN
HIGH TO THE WEST AND A STRONG COLD FRONT PUSHING SOUTH THROUGH THE
GREAT LAKES CAN SUPPORT BETTER LAKE EFFECT POTENTIAL FOR SOME OF
OUR LAKE ADJACENT AREAS...AT THIS TIME MORE SO FAR NORTHWEST
INDIANA. OVERALL THOUGH BECAUSE OF THE NORTHWEST FLOW...THE THREAT
OF WIDESPREAD HIGH IMPACT WEATHER LOOKS LOW AT THIS TIME.

MTF

&&

.AVIATION...
FOR THE 18Z TAFS...

UPPER LEVEL LOW OVER LAKE MICHIGAN EARLY THIS AFTERNOON WILL
CONTINUE TO SLOWLY MEANDER EASTWARD ACROSS THE GREAT LAKES TODAY
AND TOMORROW WITH PINWHEELING UPPER LEVEL DISTURBANCES BRINGING
PERIODIC CHANCES FOR LIGHT SNOW SHOWERS AND FLURRIES TO THE
REGION. ONE OF THESE WAVES IS NOW DROPPING SOUTH INTO CENTRAL
ILLINOIS WHICH SHOULD ALLOW A LULL IN THE SNOW ACTIVITY IN ITS
WAKE THROUGH THE REST OF THE AFTERNOON. ANOTHER WAVE IS PROGGED TO
ROTATE ACROSS THE TERMINALS LATE THIS EVENING AND TONIGHT. FORCING
IS FAIRLY WEAK HOWEVER LOW LEVEL MOISTURE IS FOCUSED WITHIN A
RELATIVELY DEEP SNOW GROWTH ZONE WHICH SHOULD ALLOW FOR EFFICIENT
SNOW PRODUCTION. CONFIDENCE IN THE TIMING DETAILS REMAINS FAIRLY
LOW THOUGH GIVEN THE RATHER BENIGN FORCING. DURING THE DAY
TUESDAY...COLD AIR SPILLING INTO THE REGION WILL RESULT IN
STEEPENING LOW LEVEL LAPSE RATES AND ONCE AGAIN PRIME THE
ATMOSPHERE FOR DECENT SNOW PRODUCTION IF WE REALIZE ANY
FORCING...HOWEVER ANY FORCING CONTINUES TO BE WEAK RESULTING IN
CONSIDERABLE UNCERTAINTY SO FOR NOW WILL JUST INTRODUCE A PROB30
FOR SNOW EARLY TO MID AFTERNOON. WINDS WILL REMAIN OUT OF THE
NORTHWEST THROUGH THE PERIOD...WITH GUSTS INCREASING LATE THIS
AFTERNOON INTO EARLY EVENING. EXPECT CIGS TO REMAIN MVFR THROUGH
THE PERIOD.

BMD

&&

.MARINE...
223 PM CST

LOW PRESSURE CENTERED NEAR LAKE HURON/LAKE ONTARIO EARLY THIS
AFTERNOON WILL VERY GRADUALLY MEANDER TOWARDS LAKE ONTARIO BY
TOMORROW NIGHT WITH MODERATELY STRONG NORTH TO NORTHWEST WINDS
EXPECTED TO BE IN PLACE ACROSS LAKE MICHIGAN. WINDS ARE EXPECTED
TO REMAIN AROUND 30 KT THIS EVENING THROUGH WEDNESDAY
NIGHT...WITH A FEW GALE FORCE GUSTS POSSIBLE MAINLY TUESDAY INTO
TUESDAY NIGHT. FREEZING SPRAY IS ALSO A CONCERN TUESDAY THROUGH
WEDNESDAY EVENING. HIGH PRESSURE WILL BUILD FROM THE UPPER
MIDWEST WEDNESDAY NIGHT INTO THE OHIO VALLEY THURSDAY NIGHT
RESULTING A MODEST TAPERING OF THE WINDS AS THEY BACK TO THE WEST.
ANOTHER COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN FRIDAY TURNING
WINDS BACK TO NORTHERLY AND PICKING UP ONCE AGAIN. THIS FRONT WILL
USHER IN A BITTERLY COLD ARCTIC AIRMASS WHICH COULD RESULT IN
ADDITIONAL GALES...PARTICULARLY FRIDAY NIGHT...AND FREEZING SPRAY
ACROSS LAKE MICHIGAN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 082050
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CST MON FEB 8 2016


.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
340 AM CST

WEDNESDAY NIGHT THROUGH MONDAY...

THE PATTERN CONTINUES TO LOOK LIKE A COOLER THAN NORMAL ONE IN
THIS TIME PERIOD. THE ELEVATED BAROCLINIC ZONE ON THE WESTERN SIDE
OF THE EASTERN NORTH AMERICAN TROUGH LOOKS TO BE UNSETTLED WITH
SEVERAL RIPPLES SUPPORTING OCCASIONAL LIGHT SNOW
CHANCES...ALTHOUGH THE PLACEMENT OF THAT HAS LARGE SPREAD IN
GUIDANCE AT THIS TIME. AN EVEN MORE ANOMALOUS UPPER LEVEL LOW IS
FORECAST TO DIG INTO EASTERN CANADA BY FRIDAY OR SATURDAY...WITH
THE EC FURTHER SOUTH WITH THIS FEATURE. THIS RESULTS IN SOME
DIFFERENCES IN THE SURFACE PRESSURE FIELDS BETWEEN THE GFS AND
EC...THOUGH THE GENERAL SYNOPTIC PATTERN WITH A STRONG CANADIAN
HIGH TO THE WEST AND A STRONG COLD FRONT PUSHING SOUTH THROUGH THE
GREAT LAKES CAN SUPPORT BETTER LAKE EFFECT POTENTIAL FOR SOME OF
OUR LAKE ADJACENT AREAS...AT THIS TIME MORE SO FAR NORTHWEST
INDIANA. OVERALL THOUGH BECAUSE OF THE NORTHWEST FLOW...THE THREAT
OF WIDESPREAD HIGH IMPACT WEATHER LOOKS LOW AT THIS TIME.

MTF

&&

.AVIATION...
FOR THE 18Z TAFS...

UPPER LEVEL LOW OVER LAKE MICHIGAN EARLY THIS AFTERNOON WILL
CONTINUE TO SLOWLY MEANDER EASTWARD ACROSS THE GREAT LAKES TODAY
AND TOMORROW WITH PINWHEELING UPPER LEVEL DISTURBANCES BRINGING
PERIODIC CHANCES FOR LIGHT SNOW SHOWERS AND FLURRIES TO THE
REGION. ONE OF THESE WAVES IS NOW DROPPING SOUTH INTO CENTRAL
ILLINOIS WHICH SHOULD ALLOW A LULL IN THE SNOW ACTIVITY IN ITS
WAKE THROUGH THE REST OF THE AFTERNOON. ANOTHER WAVE IS PROGGED TO
ROTATE ACROSS THE TERMINALS LATE THIS EVENING AND TONIGHT. FORCING
IS FAIRLY WEAK HOWEVER LOW LEVEL MOISTURE IS FOCUSED WITHIN A
RELATIVELY DEEP SNOW GROWTH ZONE WHICH SHOULD ALLOW FOR EFFICIENT
SNOW PRODUCTION. CONFIDENCE IN THE TIMING DETAILS REMAINS FAIRLY
LOW THOUGH GIVEN THE RATHER BENIGN FORCING. DURING THE DAY
TUESDAY...COLD AIR SPILLING INTO THE REGION WILL RESULT IN
STEEPENING LOW LEVEL LAPSE RATES AND ONCE AGAIN PRIME THE
ATMOSPHERE FOR DECENT SNOW PRODUCTION IF WE REALIZE ANY
FORCING...HOWEVER ANY FORCING CONTINUES TO BE WEAK RESULTING IN
CONSIDERABLE UNCERTAINTY SO FOR NOW WILL JUST INTRODUCE A PROB30
FOR SNOW EARLY TO MID AFTERNOON. WINDS WILL REMAIN OUT OF THE
NORTHWEST THROUGH THE PERIOD...WITH GUSTS INCREASING LATE THIS
AFTERNOON INTO EARLY EVENING. EXPECT CIGS TO REMAIN MVFR THROUGH
THE PERIOD.

BMD

&&

.MARINE...
223 PM CST

LOW PRESSURE CENTERED NEAR LAKE HURON/LAKE ONTARIO EARLY THIS
AFTERNOON WILL VERY GRADUALLY MEANDER TOWARDS LAKE ONTARIO BY
TOMORROW NIGHT WITH MODERATELY STRONG NORTH TO NORTHWEST WINDS
EXPECTED TO BE IN PLACE ACROSS LAKE MICHIGAN. WINDS ARE EXPECTED
TO REMAIN AROUND 30 KT THIS EVENING THROUGH WEDNESDAY
NIGHT...WITH A FEW GALE FORCE GUSTS POSSIBLE MAINLY TUESDAY INTO
TUESDAY NIGHT. FREEZING SPRAY IS ALSO A CONCERN TUESDAY THROUGH
WEDNESDAY EVENING. HIGH PRESSURE WILL BUILD FROM THE UPPER
MIDWEST WEDNESDAY NIGHT INTO THE OHIO VALLEY THURSDAY NIGHT
RESULTING A MODEST TAPERING OF THE WINDS AS THEY BACK TO THE WEST.
ANOTHER COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN FRIDAY TURNING
WINDS BACK TO NORTHERLY AND PICKING UP ONCE AGAIN. THIS FRONT WILL
USHER IN A BITTERLY COLD ARCTIC AIRMASS WHICH COULD RESULT IN
ADDITIONAL GALES...PARTICULARLY FRIDAY NIGHT...AND FREEZING SPRAY
ACROSS LAKE MICHIGAN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 082050
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CST MON FEB 8 2016


.SHORT TERM...
250 PM CST

TONIGHT THROUGH WEDNESDAY...

SNOW/SNOW SHOWER TRENDS AND ACCUMULATIONS...INDIANA LAKE EFFECT
SNOW...AND COLDER TEMPERATURES ARE THE MAIN FORECAST CONCERNS
THROUGH MID-WEEK.

DEEP CLOSED UPPER LOW WAS OVER THE REGION THIS AFTERNOON WITHIN
LARGE EASTERN NORTH AMERICAN UPPER TROUGH. SEVERAL VORTICITY LOBES
WERE ROTATING ABOUT THIS FEATURE...AND ALONG STEEP LOW LEVEL LAPSE
RATES DUE TO STRONG COLD ADVECTION WILL BE THE MAIN MODULATING
FACTORS IN COVERAGE AND INTENSITY OF LIGHT SNOW/SNOW SHOWERS OVER
THE NEXT COUPLE OF DAYS. ONE SUCH WAVE WAS NOTED IN WATER VAPOR
IMAGERY CURRENTLY MOVING SOUTHEAST ACROSS CENTRAL IL...WITH A
CORRESPONDING AREA OF LIGHT SNOW ACROSS SOUTHERN PARTS OF THE
FORECAST AREA THIS AFTERNOON. ANOTHER AXIS OF SHEARED VORTICITY
WAS OVER LAKE MICHIGAN AND EASTERN WISCONSIN WITH ANOTHER BATCH OF
SNOW SHOWERS. FLURRIES WERE LIKELY OCCURRING IN MOST OTHER AREAS
IN SATURATED COLD AIR MASS. LIGHT SNOW WILL LIKELY CONTINUE TO
AFFECT SOUTHERN PARTS OF THE FA FOR THE REMAINDER OF THE AFTERNOON
AS THE CENTRAL IL WAVE CONTINUES TO MOVE OFF TO THE
SOUTHEAST...WITH LIGHT SNOW/SNOW SHOWERS EXPECTED TO INCREASE FROM
THE NORTH AGAIN THIS EVENING/OVERNIGHT AS SHEARED VORT TO OUR
NORTH WRAPS SOUTH-SOUTHEAST AROUND UPPER LOW CENTER WHICH DEVELOPS
ACROSS NORTHEAST INDIANA/NORTHWEST OHIO. THIS UPPER LOW WILL
SLOWLY LIFT OUT TO THE EAST-NORTHEAST ON TUESDAY...WITH ANOTHER
SHORT WAVE DROPPING INTO THE TRAILING PORTION OF THE UPPER TROUGH
AND ACROSS ESPECIALLY EASTERN PARTS OF THE FORECAST AREA TUESDAY
NIGHT. MODEL QPF AMOUNTS REMAIN GENERALLY LIGHT...WITH NON-UNIFORM
COVERAGE DUE TO EXPECTED OFTEN SHOWERY NATURE OF PRECIP.
OVERALL...IT STILL APPEARS THAT WIDESPREAD SNOWFALL OF AN INCH TO
PERHAPS 2-3 INCHES ARE LIKELY BY THE TIME MEASURABLE PRECIP SHIFTS
EAST OF THE AREA LATE TUESDAY NIGHT...GENERALLY LOWEST FAR WEST
AND HIGHER ACROSS THE EAST PARTS OF THE CWA.

WITHIN THIS WEATHER REGIME...CONTINUED COLD ADVECTION WILL RESULT
IN LAKE-EFFECT SNOW SHOWERS DEVELOPING ACROSS PARTS OF NORTHWEST
INDIANA TONIGHT...AND MOST LIKELY CONTINUING INTO THURSDAY MORNING
AT LEAST IN LIGHTER FASHION UNTIL LOW LEVEL WINDS BACK TO THE
WEST. THERMODYNAMICS BECOME FAVORABLE FOR LAKE SNOW SHOWERS THIS
EVENING... AS LAKE SURFACE TO 850 MB DELTA-T INCREASES TO AROUND
20 C/KM BY TUESDAY MORNING. COMBINED WITH WITH DEEPER FORCING
PROVIDED BY AFOREMENTIONED VORT LOBE...THE POTENTIAL FOR HEAVIER
SNOW SHOWERS LOOKS TO BE FROM LATER TONIGHT/EARLY TUESDAY...AND
AGAIN TUESDAY NIGHT INTO WEDNESDAY. LOW LEVEL CONVERGENCE AND
FETCH CONTINUE TO FAVOR MAINLY NORTHEAST PORTIONS OF PORTER
COUNTY...WITH THE AXIS OF HEAVIEST SNOW EXPECTED TO BE ACROSS LA
PORTE AND BERRIEN COUNTIES TO THE EAST OF THE CWA. NORTHEAST
PORTER COUNTY DOES HAVE THE POTENTIAL FOR SEVERAL INCHES OF
ACCUMULATION DURING THE PERIOD...DEPENDING UPON LOCATION/INTENSITY
OF BANDING. LONG DURATION OF LIGHT/OCCASIONALLY MODERATE SNOW
SHOWERS TOTALING PERHAPS 4+ INCHES DOES NOT APPEAR TO WARRANT
HEADLINES AT THIS POINT...THOUGH WILL CONTINUE TO MENTION BOTH THE
LAKE EFFECT AND THE POTENTIAL FOR TUESDAY MORNING RUSH HOUR IMPACT
IN AN SPS.

TEMPERATURES VERY SLOWLY FALLING INTO THE LOW-MID 20S THIS
AFTERNOON...AND WILL CONTINUE TO FALL OFF INTO THE TEENS IN MOST
AREAS TONIGHT. LITTLE RECOVERY IS EXPECTED TUESDAY AS COLD
ADVECTION PERSISTS...WITH COLD AIR LINGERING THROUGH MID-WEEK WITH
OVERNIGHT LOWS IN THE SINGLE DIGIT AND HIGHS IN THE TEEENS BY
WEDNESDAY.

RATZER

&&

.LONG TERM...
340 AM CST

WEDNESDAY NIGHT THROUGH MONDAY...

THE PATTERN CONTINUES TO LOOK LIKE A COOLER THAN NORMAL ONE IN
THIS TIME PERIOD. THE ELEVATED BAROCLINIC ZONE ON THE WESTERN SIDE
OF THE EASTERN NORTH AMERICAN TROUGH LOOKS TO BE UNSETTLED WITH
SEVERAL RIPPLES SUPPORTING OCCASIONAL LIGHT SNOW
CHANCES...ALTHOUGH THE PLACEMENT OF THAT HAS LARGE SPREAD IN
GUIDANCE AT THIS TIME. AN EVEN MORE ANOMALOUS UPPER LEVEL LOW IS
FORECAST TO DIG INTO EASTERN CANADA BY FRIDAY OR SATURDAY...WITH
THE EC FURTHER SOUTH WITH THIS FEATURE. THIS RESULTS IN SOME
DIFFERENCES IN THE SURFACE PRESSURE FIELDS BETWEEN THE GFS AND
EC...THOUGH THE GENERAL SYNOPTIC PATTERN WITH A STRONG CANADIAN
HIGH TO THE WEST AND A STRONG COLD FRONT PUSHING SOUTH THROUGH THE
GREAT LAKES CAN SUPPORT BETTER LAKE EFFECT POTENTIAL FOR SOME OF
OUR LAKE ADJACENT AREAS...AT THIS TIME MORE SO FAR NORTHWEST
INDIANA. OVERALL THOUGH BECAUSE OF THE NORTHWEST FLOW...THE THREAT
OF WIDESPREAD HIGH IMPACT WEATHER LOOKS LOW AT THIS TIME.

MTF

&&

.AVIATION...
FOR THE 18Z TAFS...

UPPER LEVEL LOW OVER LAKE MICHIGAN EARLY THIS AFTERNOON WILL
CONTINUE TO SLOWLY MEANDER EASTWARD ACROSS THE GREAT LAKES TODAY
AND TOMORROW WITH PINWHEELING UPPER LEVEL DISTURBANCES BRINGING
PERIODIC CHANCES FOR LIGHT SNOW SHOWERS AND FLURRIES TO THE
REGION. ONE OF THESE WAVES IS NOW DROPPING SOUTH INTO CENTRAL
ILLINOIS WHICH SHOULD ALLOW A LULL IN THE SNOW ACTIVITY IN ITS
WAKE THROUGH THE REST OF THE AFTERNOON. ANOTHER WAVE IS PROGGED TO
ROTATE ACROSS THE TERMINALS LATE THIS EVENING AND TONIGHT. FORCING
IS FAIRLY WEAK HOWEVER LOW LEVEL MOISTURE IS FOCUSED WITHIN A
RELATIVELY DEEP SNOW GROWTH ZONE WHICH SHOULD ALLOW FOR EFFICIENT
SNOW PRODUCTION. CONFIDENCE IN THE TIMING DETAILS REMAINS FAIRLY
LOW THOUGH GIVEN THE RATHER BENIGN FORCING. DURING THE DAY
TUESDAY...COLD AIR SPILLING INTO THE REGION WILL RESULT IN
STEEPENING LOW LEVEL LAPSE RATES AND ONCE AGAIN PRIME THE
ATMOSPHERE FOR DECENT SNOW PRODUCTION IF WE REALIZE ANY
FORCING...HOWEVER ANY FORCING CONTINUES TO BE WEAK RESULTING IN
CONSIDERABLE UNCERTAINTY SO FOR NOW WILL JUST INTRODUCE A PROB30
FOR SNOW EARLY TO MID AFTERNOON. WINDS WILL REMAIN OUT OF THE
NORTHWEST THROUGH THE PERIOD...WITH GUSTS INCREASING LATE THIS
AFTERNOON INTO EARLY EVENING. EXPECT CIGS TO REMAIN MVFR THROUGH
THE PERIOD.

BMD

&&

.MARINE...
223 PM CST

LOW PRESSURE CENTERED NEAR LAKE HURON/LAKE ONTARIO EARLY THIS
AFTERNOON WILL VERY GRADUALLY MEANDER TOWARDS LAKE ONTARIO BY
TOMORROW NIGHT WITH MODERATELY STRONG NORTH TO NORTHWEST WINDS
EXPECTED TO BE IN PLACE ACROSS LAKE MICHIGAN. WINDS ARE EXPECTED
TO REMAIN AROUND 30 KT THIS EVENING THROUGH WEDNESDAY
NIGHT...WITH A FEW GALE FORCE GUSTS POSSIBLE MAINLY TUESDAY INTO
TUESDAY NIGHT. FREEZING SPRAY IS ALSO A CONCERN TUESDAY THROUGH
WEDNESDAY EVENING. HIGH PRESSURE WILL BUILD FROM THE UPPER
MIDWEST WEDNESDAY NIGHT INTO THE OHIO VALLEY THURSDAY NIGHT
RESULTING A MODEST TAPERING OF THE WINDS AS THEY BACK TO THE WEST.
ANOTHER COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN FRIDAY TURNING
WINDS BACK TO NORTHERLY AND PICKING UP ONCE AGAIN. THIS FRONT WILL
USHER IN A BITTERLY COLD ARCTIC AIRMASS WHICH COULD RESULT IN
ADDITIONAL GALES...PARTICULARLY FRIDAY NIGHT...AND FREEZING SPRAY
ACROSS LAKE MICHIGAN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 082025
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
225 PM CST MON FEB 8 2016

.UPDATE...
1128 AM CST

FOR MORNING UPDATE...

HAVE UPDATED TEMPERATURE TRENDS TODAY...WITH READINGS ALREADY
BEGINNING TO FALL FROM MORNING HIGHS. GFS LAMP GUIDANCE SEEMS TO
BE CAPTURING THIS NICELY AND HAVE USED THIS TO DEPICT A SLOW FALL
INTO THE LOWER AND MIDDLE 20S THROUGH LATE AFTERNOON. WINDS ALSO
PICKING UP FROM THE WEST BEHIND SECONDARY COLD FRONT ESPECIALLY
ACROSS THE WESTERN PORTIONS OF THE CWA...WHERE WIND CHILLS WILL
FALL TO THE SINGLE DIGITS AND LOWER TEENS THIS AFTERNOON.
OTHERWISE...FORECAST OF FLURRIES AND SNOW SHOWERS REMAINS
APPROPRIATE FOR THE CURRENT WEATHER REGIME WITH COLD ADVECTION
STEEPENING LOW LEVEL LAPSE RATES AND A SERIES OF MID-LEVEL VORT
CIRCULATIONS HELPING TO MODULATE COVERAGE AND INTENSITY OF
GENERALLY LIGHT SNOW. UPDATED GRIDS/ZFP AVAILABLE.

RATZER

&&

.SHORT TERM...
337 AM CST

THROUGH WEDNESDAY...

THE FORECAST DETAILS AND OVERALL MESSAGE REMAIN SIMILAR FOR THE
UPCOMING LONG DURATION LIGHT SNOW EVENT WITHIN A MORE BLUSTERY
AND COLDER PATTERN. HAVE HONED FURTHER IN ON THIS EVENING THROUGH
TUESDAY MORNING AS A PROBABLE TIME FOR WIDESPREAD LIGHT SNOW WITH
ACCUMULATIONS...WITH TODAY SEEING MORE FLURRIES AND OCCASIONAL
SNOW SHOWERS. WITH THE OVER 30 HOURS EXPECTED OF OFF AND ON
SNOW...ACCUMULATIONS CONTINUE TO LOOK ON THE ORDER OF ONE HALF TO
2.5 INCHES FOR MOST AREAS. IN GENERAL...HIGHER TOTALS LOOK
EAST...ALTHOUGH SNOWFALL TOTALS TEND TO END UP LIKE A WRINKLED
SHEET AND NOT NICE AND SMOOTH /BORROWED THAT FROM A COLLEAGUE/.
FINALLY...PORTER COUNTY INDIANA STILL LOOKS TO HAVE LAKE EFFECT
ENHANCEMENT THAT WILL BRING SNOWFALL TOTALS UP.

ONE OF THE MORE PRONOUNCED COLD CORE UPPER LOWS OF THIS WINTER IS
ROTATING ITS WAY SOUTHEASTWARD ACROSS THE WESTERN GREAT LAKES
EARLY THIS MORNING. LARGE SCALE WATER VAPOR IMAGERY REVEALS THE
UPPER JET MAXIMUM IS STILL ROUNDING THE TOP OF THE WESTERN NORTH
AMERICAN RIDGE WITH THE RIDGE CONTINUING TO BUILD. AS A
RESULT...THE GREAT LAKES TROUGH WILL CONTINUE TO DIG AND PROGRESS
SOUTHEAST THROUGH TONIGHT AS THAT JET HEADS DUE SOUTH OVER THE
PLAINS. IN ADDITION...THE DEEP LOW OFF THE EASTERN SEABOARD WILL
FURTHER KEEP OUR UPPER LOW FROM PROGRESSING QUICKLY
EAST...ASSISTING IN THE BUILDING CHILL AND LONG DURATION LIGHT
SNOW.

THE PRIMARY SURFACE COLD FRONT WILL CLEAR THE AREA SOON AFTER
DAYBREAK WITH TEMPERATURES INCHING DOWNWARD A FEW DEGREES AND THEN
LIKELY NOT TO RECOVER MUCH TODAY...WITH THE AFTERNOON IN THE MID
20S TO LOWER 30S FOR MOST. STEEP LOW-LEVEL LAPSE RATES BEHIND
THIS FRONT ARE ASSISTING IN WIDESPREAD FLURRIES ENTERING NORTHERN
ILLINOIS PER RADAR AND OBSERVATIONS...WITH A SCATTERING OF
EMBEDDED HIGHER REFLECTIVITY AND MORE SNOW SHOWER-ISH ACTIVITY.
AM EXPECTING THIS TO BASICALLY BE THE CASE TODAY ACROSS OUR
AREA...THAT IS FLURRIES MORE OFTEN THAN NOT...WITH OCCASIONAL TRUE
SNOW SHOWERS AND QUICKLY VARYING VISIBILITY. THE COVERAGE OF SNOW
SHOWERS WILL BE MODULATED BY A HANDFUL OF FACTORS...WITH VORTICITY
MAXIMAS PROBABLY THE SIMPLEST TO KEY IN ON...WITH OTHERS BEING
MORE MESOSCALE /E.G. LOW-LEVEL F-GEN/. THESE FACTORS WITHIN SOME
OF THE HIGH-RES HOURLY GUIDANCE THROUGH TODAY WOULD POINT TOWARD
SLIGHTLY BETTER TRUE SNOW SHOWER COVERAGE OVER THE WESTERN AND
SOUTHERN CWA. BUT AGAIN TOUGH TO TIME EXACTLY SO A BROAD
CONSISTENT FORECAST MESSAGE FOR TODAY.

STRONGER SYNOPTIC LIFT...SLIGHTLY BETTER LAPSE RATES...AND A MORE
FAVORABLE THERMAL PROFILE FOR DENDRITES ALL ARRIVE EARLY THIS
EVENING FROM NORTH TO SOUTH AS A VORTICITY LOBE ROTATES
SOUTHWARD. THE MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH
THIS AND HAVE JUST GONE LIGHT SNOW AREAWIDE. THIS FOR NORTHERN
AREAS WILL LIKELY OVERLAP AT LEAST PART OF THE EVENING COMMUTE
AND A PERSISTENT...THOUGH LIGHT...ACCUMULATION IS LIKELY TO BEGIN
IN THAT TIME. ITS MORE CHALLENGING TO SAY WHEN THIS PERIOD WILL
END...BUT IT LOOKS TO CONTINUE INTO TUESDAY MORNING. WITH
NORTHWEST LOW-LEVEL WINDS HAVING INCREASED ON RE-ENFORCED COLD
ADVECTION...VISIBILITY COULD BE LOW TO QUITE LOW AT TIMES. SO WITH
POSSIBLE TWO COMMUTES LIKELY TO BE DEALING WITH LIGHT ACCUMULATING
SNOW AND SOME VARYING VISIBILITY HAVE GONE AHEAD AND ISSUED AN SPS
TO FURTHER THE MESSAGE.

LOW-LEVEL WINDS WILL TURN OFF THE LAKE IN NORTHWEST INDIANA WITH
LAKE ENHANCEMENT TO THE SNOW LIKELY INTO BOTH LAKE AND PORTER
COUNTY BY LATE TONIGHT...THOUGH THE LONGER FETCH WILL BE POINTED
INTO PORTER COUNTY. EQUILIBRIUM LEVELS ARE FORECAST TO BE AROUND
8000 FT THOUGH WITH A GRADUALLY DEEPENING DENDRITIC GROWTH LAYER.
SO THIS WILL HELP ACCUMULATIONS IN THIS AREA WITH 2 TO 3 INCHES
PRESENTLY FAVORED IN THE FAR NORTHEAST PART OF THE COUNTY BY
TUESDAY EVENING...AND ADDITIONAL AFTER THAT POINT LATE TUESDAY
NIGHT INTO WEDNESDAY...POSSIBLY EVEN A FEW MORE INCHES. WILL NEED
TO MONITOR IF A HEADLINE IS NEEDED...PARTICULARLY IF RATES ARE
MORE ENHANCED...ALTHOUGH THE BETTER LAKE EFFECT SETUP CONTINUES TO
LOOK FURTHER EAST...SO NOT ANTICIPATING IT AT THIS TIME.

TEMPERATURES LOOK TO NOT CLIMB AT ALL ON TUESDAY WITH WIND CHILLS
IN THE SINGLE DIGITS. CYCLONIC FLOW PERSISTS THROUGH WEDNESDAY SO
CONTINUE TO LEAN CLOUDIER THAN GUIDANCE INTO THEN. IF CLOUDS CAN
CLEAR BY WEDNESDAY NIGHT...THAT LOOKS TO BE A PARTICULARLY CHILLY
NIGHT WITH SOME OUTLYING AREAS POTENTIALLY DROPPING TO OR BELOW
ZERO.

MTF

&&

.LONG TERM...
340 AM CST

WEDNESDAY NIGHT THROUGH MONDAY...

THE PATTERN CONTINUES TO LOOK LIKE A COOLER THAN NORMAL ONE IN
THIS TIME PERIOD. THE ELEVATED BAROCLINIC ZONE ON THE WESTERN SIDE
OF THE EASTERN NORTH AMERICAN TROUGH LOOKS TO BE UNSETTLED WITH
SEVERAL RIPPLES SUPPORTING OCCASIONAL LIGHT SNOW
CHANCES...ALTHOUGH THE PLACEMENT OF THAT HAS LARGE SPREAD IN
GUIDANCE AT THIS TIME. AN EVEN MORE ANOMALOUS UPPER LEVEL LOW IS
FORECAST TO DIG INTO EASTERN CANADA BY FRIDAY OR SATURDAY...WITH
THE EC FURTHER SOUTH WITH THIS FEATURE. THIS RESULTS IN SOME
DIFFERENCES IN THE SURFACE PRESSURE FIELDS BETWEEN THE GFS AND
EC...THOUGH THE GENERAL SYNOPTIC PATTERN WITH A STRONG CANADIAN
HIGH TO THE WEST AND A STRONG COLD FRONT PUSHING SOUTH THROUGH THE
GREAT LAKES CAN SUPPORT BETTER LAKE EFFECT POTENTIAL FOR SOME OF
OUR LAKE ADJACENT AREAS...AT THIS TIME MORE SO FAR NORTHWEST
INDIANA. OVERALL THOUGH BECAUSE OF THE NORTHWEST FLOW...THE THREAT
OF WIDESPREAD HIGH IMPACT WEATHER LOOKS LOW AT THIS TIME.

MTF

&&

.AVIATION...
FOR THE 18Z TAFS...

UPPER LEVEL LOW OVER LAKE MICHIGAN EARLY THIS AFTERNOON WILL
CONTINUE TO SLOWLY MEANDER EASTWARD ACROSS THE GREAT LAKES TODAY
AND TOMORROW WITH PINWHEELING UPPER LEVEL DISTURBANCES BRINGING
PERIODIC CHANCES FOR LIGHT SNOW SHOWERS AND FLURRIES TO THE
REGION. ONE OF THESE WAVES IS NOW DROPPING SOUTH INTO CENTRAL
ILLINOIS WHICH SHOULD ALLOW A LULL IN THE SNOW ACTIVITY IN ITS
WAKE THROUGH THE REST OF THE AFTERNOON. ANOTHER WAVE IS PROGGED TO
ROTATE ACROSS THE TERMINALS LATE THIS EVENING AND TONIGHT. FORCING
IS FAIRLY WEAK HOWEVER LOW LEVEL MOISTURE IS FOCUSED WITHIN A
RELATIVELY DEEP SNOW GROWTH ZONE WHICH SHOULD ALLOW FOR EFFICIENT
SNOW PRODUCTION. CONFIDENCE IN THE TIMING DETAILS REMAINS FAIRLY
LOW THOUGH GIVEN THE RATHER BENIGN FORCING. DURING THE DAY
TUESDAY...COLD AIR SPILLING INTO THE REGION WILL RESULT IN
STEEPENING LOW LEVEL LAPSE RATES AND ONCE AGAIN PRIME THE
ATMOSPHERE FOR DECENT SNOW PRODUCTION IF WE REALIZE ANY
FORCING...HOWEVER ANY FORCING CONTINUES TO BE WEAK RESULTING IN
CONSIDERABLE UNCERTAINTY SO FOR NOW WILL JUST INTRODUCE A PROB30
FOR SNOW EARLY TO MID AFTERNOON. WINDS WILL REMAIN OUT OF THE
NORTHWEST THROUGH THE PERIOD...WITH GUSTS INCREASING LATE THIS
AFTERNOON INTO EARLY EVENING. EXPECT CIGS TO REMAIN MVFR THROUGH
THE PERIOD.

BMD

&&

.MARINE...
223 PM CST

LOW PRESSURE CENTERED NEAR LAKE HURON/LAKE ONTARIO EARLY THIS
AFTERNOON WILL VERY GRADUALLY MEANDER TOWARDS LAKE ONTARIO BY
TOMORROW NIGHT WITH MODERATELY STRONG NORTH TO NORTHWEST WINDS
EXPECTED TO BE IN PLACE ACROSS LAKE MICHIGAN. WINDS ARE EXPECTED
TO REMAIN AROUND 30 KT THIS EVENING THROUGH WEDNESDAY
NIGHT...WITH A FEW GALE FORCE GUSTS POSSIBLE MAINLY TUESDAY INTO
TUESDAY NIGHT. FREEZING SPRAY IS ALSO A CONCERN TUESDAY THROUGH
WEDNESDAY EVENING. HIGH PRESSURE WILL BUILD FROM THE UPPER
MIDWEST WEDNESDAY NIGHT INTO THE OHIO VALLEY THURSDAY NIGHT
RESULTING A MODEST TAPERING OF THE WINDS AS THEY BACK TO THE WEST.
ANOTHER COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN FRIDAY TURNING
WINDS BACK TO NORTHERLY AND PICKING UP ONCE AGAIN. THIS FRONT WILL
USHER IN A BITTERLY COLD ARCTIC AIRMASS WHICH COULD RESULT IN
ADDITIONAL GALES...PARTICULARLY FRIDAY NIGHT...AND FREEZING SPRAY
ACROSS LAKE MICHIGAN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 081738
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1138 AM CST MON FEB 8 2016

.UPDATE...
1128 AM CST

FOR MORNING UPDATE...

HAVE UPDATED TEMPERATURE TRENDS TODAY...WITH READINGS ALREADY
BEGINNING TO FALL FROM MORNING HIGHS. GFS LAMP GUIDANCE SEEMS TO
BE CAPTURING THIS NICELY AND HAVE USED THIS TO DEPICT A SLOW FALL
INTO THE LOWER AND MIDDLE 20S THROUGH LATE AFTERNOON. WINDS ALSO
PICKING UP FROM THE WEST BEHIND SECONDARY COLD FRONT ESPECIALLY
ACROSS THE WESTERN PORTIONS OF THE CWA...WHERE WIND CHILLS WILL
FALL TO THE SINGLE DIGITS AND LOWER TEENS THIS AFTERNOON.
OTHERWISE...FORECAST OF FLURRIES AND SNOW SHOWERS REMAINS
APPROPRIATE FOR THE CURRENT WEATHER REGIME WITH COLD ADVECTION
STEEPENING LOW LEVEL LAPSE RATES AND A SERIES OF MID-LEVEL VORT
CIRCULATIONS HELPING TO MODULATE COVERAGE AND INTENSITY OF
GENERALLY LIGHT SNOW. UPDATED GRIDS/ZFP AVAILABLE.

RATZER

&&

.SHORT TERM...
337 AM CST

THROUGH WEDNESDAY...

THE FORECAST DETAILS AND OVERALL MESSAGE REMAIN SIMILAR FOR THE
UPCOMING LONG DURATION LIGHT SNOW EVENT WITHIN A MORE BLUSTERY
AND COLDER PATTERN. HAVE HONED FURTHER IN ON THIS EVENING THROUGH
TUESDAY MORNING AS A PROBABLE TIME FOR WIDESPREAD LIGHT SNOW WITH
ACCUMULATIONS...WITH TODAY SEEING MORE FLURRIES AND OCCASIONAL
SNOW SHOWERS. WITH THE OVER 30 HOURS EXPECTED OF OFF AND ON
SNOW...ACCUMULATIONS CONTINUE TO LOOK ON THE ORDER OF ONE HALF TO
2.5 INCHES FOR MOST AREAS. IN GENERAL...HIGHER TOTALS LOOK
EAST...ALTHOUGH SNOWFALL TOTALS TEND TO END UP LIKE A WRINKLED
SHEET AND NOT NICE AND SMOOTH /BORROWED THAT FROM A COLLEAGUE/.
FINALLY...PORTER COUNTY INDIANA STILL LOOKS TO HAVE LAKE EFFECT
ENHANCEMENT THAT WILL BRING SNOWFALL TOTALS UP.

ONE OF THE MORE PRONOUNCED COLD CORE UPPER LOWS OF THIS WINTER IS
ROTATING ITS WAY SOUTHEASTWARD ACROSS THE WESTERN GREAT LAKES
EARLY THIS MORNING. LARGE SCALE WATER VAPOR IMAGERY REVEALS THE
UPPER JET MAXIMUM IS STILL ROUNDING THE TOP OF THE WESTERN NORTH
AMERICAN RIDGE WITH THE RIDGE CONTINUING TO BUILD. AS A
RESULT...THE GREAT LAKES TROUGH WILL CONTINUE TO DIG AND PROGRESS
SOUTHEAST THROUGH TONIGHT AS THAT JET HEADS DUE SOUTH OVER THE
PLAINS. IN ADDITION...THE DEEP LOW OFF THE EASTERN SEABOARD WILL
FURTHER KEEP OUR UPPER LOW FROM PROGRESSING QUICKLY
EAST...ASSISTING IN THE BUILDING CHILL AND LONG DURATION LIGHT
SNOW.

THE PRIMARY SURFACE COLD FRONT WILL CLEAR THE AREA SOON AFTER
DAYBREAK WITH TEMPERATURES INCHING DOWNWARD A FEW DEGREES AND THEN
LIKELY NOT TO RECOVER MUCH TODAY...WITH THE AFTERNOON IN THE MID
20S TO LOWER 30S FOR MOST. STEEP LOW-LEVEL LAPSE RATES BEHIND
THIS FRONT ARE ASSISTING IN WIDESPREAD FLURRIES ENTERING NORTHERN
ILLINOIS PER RADAR AND OBSERVATIONS...WITH A SCATTERING OF
EMBEDDED HIGHER REFLECTIVITY AND MORE SNOW SHOWER-ISH ACTIVITY.
AM EXPECTING THIS TO BASICALLY BE THE CASE TODAY ACROSS OUR
AREA...THAT IS FLURRIES MORE OFTEN THAN NOT...WITH OCCASIONAL TRUE
SNOW SHOWERS AND QUICKLY VARYING VISIBILITY. THE COVERAGE OF SNOW
SHOWERS WILL BE MODULATED BY A HANDFUL OF FACTORS...WITH VORTICITY
MAXIMAS PROBABLY THE SIMPLEST TO KEY IN ON...WITH OTHERS BEING
MORE MESOSCALE /E.G. LOW-LEVEL F-GEN/. THESE FACTORS WITHIN SOME
OF THE HIGH-RES HOURLY GUIDANCE THROUGH TODAY WOULD POINT TOWARD
SLIGHTLY BETTER TRUE SNOW SHOWER COVERAGE OVER THE WESTERN AND
SOUTHERN CWA. BUT AGAIN TOUGH TO TIME EXACTLY SO A BROAD
CONSISTENT FORECAST MESSAGE FOR TODAY.

STRONGER SYNOPTIC LIFT...SLIGHTLY BETTER LAPSE RATES...AND A MORE
FAVORABLE THERMAL PROFILE FOR DENDRITES ALL ARRIVE EARLY THIS
EVENING FROM NORTH TO SOUTH AS A VORTICITY LOBE ROTATES
SOUTHWARD. THE MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH
THIS AND HAVE JUST GONE LIGHT SNOW AREAWIDE. THIS FOR NORTHERN
AREAS WILL LIKELY OVERLAP AT LEAST PART OF THE EVENING COMMUTE
AND A PERSISTENT...THOUGH LIGHT...ACCUMULATION IS LIKELY TO BEGIN
IN THAT TIME. ITS MORE CHALLENGING TO SAY WHEN THIS PERIOD WILL
END...BUT IT LOOKS TO CONTINUE INTO TUESDAY MORNING. WITH
NORTHWEST LOW-LEVEL WINDS HAVING INCREASED ON RE-ENFORCED COLD
ADVECTION...VISIBILITY COULD BE LOW TO QUITE LOW AT TIMES. SO WITH
POSSIBLE TWO COMMUTES LIKELY TO BE DEALING WITH LIGHT ACCUMULATING
SNOW AND SOME VARYING VISIBILITY HAVE GONE AHEAD AND ISSUED AN SPS
TO FURTHER THE MESSAGE.

LOW-LEVEL WINDS WILL TURN OFF THE LAKE IN NORTHWEST INDIANA WITH
LAKE ENHANCEMENT TO THE SNOW LIKELY INTO BOTH LAKE AND PORTER
COUNTY BY LATE TONIGHT...THOUGH THE LONGER FETCH WILL BE POINTED
INTO PORTER COUNTY. EQUILIBRIUM LEVELS ARE FORECAST TO BE AROUND
8000 FT THOUGH WITH A GRADUALLY DEEPENING DENDRITIC GROWTH LAYER.
SO THIS WILL HELP ACCUMULATIONS IN THIS AREA WITH 2 TO 3 INCHES
PRESENTLY FAVORED IN THE FAR NORTHEAST PART OF THE COUNTY BY
TUESDAY EVENING...AND ADDITIONAL AFTER THAT POINT LATE TUESDAY
NIGHT INTO WEDNESDAY...POSSIBLY EVEN A FEW MORE INCHES. WILL NEED
TO MONITOR IF A HEADLINE IS NEEDED...PARTICULARLY IF RATES ARE
MORE ENHANCED...ALTHOUGH THE BETTER LAKE EFFECT SETUP CONTINUES TO
LOOK FURTHER EAST...SO NOT ANTICIPATING IT AT THIS TIME.

TEMPERATURES LOOK TO NOT CLIMB AT ALL ON TUESDAY WITH WIND CHILLS
IN THE SINGLE DIGITS. CYCLONIC FLOW PERSISTS THROUGH WEDNESDAY SO
CONTINUE TO LEAN CLOUDIER THAN GUIDANCE INTO THEN. IF CLOUDS CAN
CLEAR BY WEDNESDAY NIGHT...THAT LOOKS TO BE A PARTICULARLY CHILLY
NIGHT WITH SOME OUTLYING AREAS POTENTIALLY DROPPING TO OR BELOW
ZERO.

MTF

&&

.LONG TERM...
340 AM CST

WEDNESDAY NIGHT THROUGH MONDAY...

THE PATTERN CONTINUES TO LOOK LIKE A COOLER THAN NORMAL ONE IN
THIS TIME PERIOD. THE ELEVATED BAROCLINIC ZONE ON THE WESTERN SIDE
OF THE EASTERN NORTH AMERICAN TROUGH LOOKS TO BE UNSETTLED WITH
SEVERAL RIPPLES SUPPORTING OCCASIONAL LIGHT SNOW
CHANCES...ALTHOUGH THE PLACEMENT OF THAT HAS LARGE SPREAD IN
GUIDANCE AT THIS TIME. AN EVEN MORE ANOMALOUS UPPER LEVEL LOW IS
FORECAST TO DIG INTO EASTERN CANADA BY FRIDAY OR SATURDAY...WITH
THE EC FURTHER SOUTH WITH THIS FEATURE. THIS RESULTS IN SOME
DIFFERENCES IN THE SURFACE PRESSURE FIELDS BETWEEN THE GFS AND
EC...THOUGH THE GENERAL SYNOPTIC PATTERN WITH A STRONG CANADIAN
HIGH TO THE WEST AND A STRONG COLD FRONT PUSHING SOUTH THROUGH THE
GREAT LAKES CAN SUPPORT BETTER LAKE EFFECT POTENTIAL FOR SOME OF
OUR LAKE ADJACENT AREAS...AT THIS TIME MORE SO FAR NORTHWEST
INDIANA. OVERALL THOUGH BECAUSE OF THE NORTHWEST FLOW...THE THREAT
OF WIDESPREAD HIGH IMPACT WEATHER LOOKS LOW AT THIS TIME.

MTF

&&

.AVIATION...
FOR THE 18Z TAFS...

UPPER LEVEL LOW OVER LAKE MICHIGAN EARLY THIS AFTERNOON WILL
CONTINUE TO SLOWLY MEANDER EASTWARD ACROSS THE GREAT LAKES TODAY
AND TOMORROW WITH PINWHEELING UPPER LEVEL DISTURBANCES BRINGING
PERIODIC CHANCES FOR LIGHT SNOW SHOWERS AND FLURRIES TO THE
REGION. ONE OF THESE WAVES IS NOW DROPPING SOUTH INTO CENTRAL
ILLINOIS WHICH SHOULD ALLOW A LULL IN THE SNOW ACTIVITY IN ITS
WAKE THROUGH THE REST OF THE AFTERNOON. ANOTHER WAVE IS PROGGED TO
ROTATE ACROSS THE TERMINALS LATE THIS EVENING AND TONIGHT. FORCING
IS FAIRLY WEAK HOWEVER LOW LEVEL MOISTURE IS FOCUSED WITHIN A
RELATIVELY DEEP SNOW GROWTH ZONE WHICH SHOULD ALLOW FOR EFFICIENT
SNOW PRODUCTION. CONFIDENCE IN THE TIMING DETAILS REMAINS FAIRLY
LOW THOUGH GIVEN THE RATHER BENIGN FORCING. DURING THE DAY
TUESDAY...COLD AIR SPILLING INTO THE REGION WILL RESULT IN
STEEPENING LOW LEVEL LAPSE RATES AND ONCE AGAIN PRIME THE
ATMOSPHERE FOR DECENT SNOW PRODUCTION IF WE REALIZE ANY
FORCING...HOWEVER ANY FORCING CONTINUES TO BE WEAK RESULTING IN
CONSIDERABLE UNCERTAINTY SO FOR NOW WILL JUST INTRODUCE A PROB30
FOR SNOW EARLY TO MID AFTERNOON. WINDS WILL REMAIN OUT OF THE
NORTHWEST THROUGH THE PERIOD...WITH GUSTS INCREASING LATE THIS
AFTERNOON INTO EARLY EVENING. EXPECT CIGS TO REMAIN MVFR THROUGH
THE PERIOD.

BMD

&&

.MARINE...
301 AM CST

ISSUED A SMALL CRAFT ADVISORY FOR TONIGHT THROUGH EARLY WEDNESDAY
NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY MORNING FOR
THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND WAVES.

A WEAK LOW OVER THE U.P. OF MI WILL DRIFT OVER THE LAKE TODAY AND
REACH THE EASTERN GREAT LAKES LATE THIS AFTERNOON.  WINDS WILL
BECOME NORTH BEHIND THE LOW AND INCREASE TO 30 KT.  HIGH PRESSURE
SINKS SOUTH OVER THE PLAINS TUESDAY NIGHT AND MOVES OVER THE
MISSISSIPPI VALLEY WEDNESDAY EVENING. THE TIGHTENED GRADIENT BETWEEN
THE HIGH AND LOW WILL RESULT IN AN EXTENDED PERIOD OF 30 KT WINDS
THROUGH WEDNESDAY NIGHT. LOW END GALE FORCE GUSTS ARE POSSIBLE LATE
TUESDAY AFTERNOON OVER THE NORTHERN HALF OF THE LAKE...AND THE GALES
REACH THE SOUTHERN END OF THE LAKE TUESDAY NIGHT.  HOWEVER...DO NOT
HAVE ENOUGH CONFIDENCE IN GALES TO ISSUE A GALE WATCH FOR TUESDAY
NIGHT INTO WEDNESDAY.  WINDS DIMINISH AS THE HIGH MOVES OVER THE
LAKE WEDNESDAY NIGHT INTO THURSDAY.

ANOTHER WEAK LOW PASSES OVER THE EASTERN GREAT LAKES THURSDAY NIGHT
AND FRIDAY WHILE HIGH PRESSURE MOVES OVER MINNESOTA FRIDAY NIGHT AND
SATURDAY.  NORTHWEST TO NORTH WINDS INCREASE TO 30 KT LATE IN THE
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 081728
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1128 AM CST MON FEB 8 2016

.UPDATE...
1128 AM CST

FOR MORNING UPDATE...

HAVE UPDATED TEMPERATURE TRENDS TODAY...WITH READINGS ALREADY
BEGINNING TO FALL FROM MORNING HIGHS. GFS LAMP GUIDANCE SEEMS TO
BE CAPTURING THIS NICELY AND HAVE USED THIS TO DEPICT A SLOW FALL
INTO THE LOWER AND MIDDLE 20S THROUGH LATE AFTERNOON. WINDS ALSO
PICKING UP FROM THE WEST BEHIND SECONDARY COLD FRONT ESPECIALLY
ACROSS THE WESTERN PORTIONS OF THE CWA...WHERE WIND CHILLS WILL
FALL TO THE SINGLE DIGITS AND LOWER TEENS THIS AFTERNOON.
OTHERWISE...FORECAST OF FLURRIES AND SNOW SHOWERS REMAINS
APPROPRIATE FOR THE CURRENT WEATHER REGIME WITH COLD ADVECTION
STEEPENING LOW LEVEL LAPSE RATES AND A SERIES OF MID-LEVEL VORT
CIRCULATIONS HELPING TO MODULATE COVERAGE AND INTENSITY OF
GENERALLY LIGHT SNOW. UPDATED GRIDS/ZFP AVAILABLE.

RATZER

&&

.SHORT TERM...
337 AM CST

THROUGH WEDNESDAY...

THE FORECAST DETAILS AND OVERALL MESSAGE REMAIN SIMILAR FOR THE
UPCOMING LONG DURATION LIGHT SNOW EVENT WITHIN A MORE BLUSTERY
AND COLDER PATTERN. HAVE HONED FURTHER IN ON THIS EVENING THROUGH
TUESDAY MORNING AS A PROBABLE TIME FOR WIDESPREAD LIGHT SNOW WITH
ACCUMULATIONS...WITH TODAY SEEING MORE FLURRIES AND OCCASIONAL
SNOW SHOWERS. WITH THE OVER 30 HOURS EXPECTED OF OFF AND ON
SNOW...ACCUMULATIONS CONTINUE TO LOOK ON THE ORDER OF ONE HALF TO
2.5 INCHES FOR MOST AREAS. IN GENERAL...HIGHER TOTALS LOOK
EAST...ALTHOUGH SNOWFALL TOTALS TEND TO END UP LIKE A WRINKLED
SHEET AND NOT NICE AND SMOOTH /BORROWED THAT FROM A COLLEAGUE/.
FINALLY...PORTER COUNTY INDIANA STILL LOOKS TO HAVE LAKE EFFECT
ENHANCEMENT THAT WILL BRING SNOWFALL TOTALS UP.

ONE OF THE MORE PRONOUNCED COLD CORE UPPER LOWS OF THIS WINTER IS
ROTATING ITS WAY SOUTHEASTWARD ACROSS THE WESTERN GREAT LAKES
EARLY THIS MORNING. LARGE SCALE WATER VAPOR IMAGERY REVEALS THE
UPPER JET MAXIMUM IS STILL ROUNDING THE TOP OF THE WESTERN NORTH
AMERICAN RIDGE WITH THE RIDGE CONTINUING TO BUILD. AS A
RESULT...THE GREAT LAKES TROUGH WILL CONTINUE TO DIG AND PROGRESS
SOUTHEAST THROUGH TONIGHT AS THAT JET HEADS DUE SOUTH OVER THE
PLAINS. IN ADDITION...THE DEEP LOW OFF THE EASTERN SEABOARD WILL
FURTHER KEEP OUR UPPER LOW FROM PROGRESSING QUICKLY
EAST...ASSISTING IN THE BUILDING CHILL AND LONG DURATION LIGHT
SNOW.

THE PRIMARY SURFACE COLD FRONT WILL CLEAR THE AREA SOON AFTER
DAYBREAK WITH TEMPERATURES INCHING DOWNWARD A FEW DEGREES AND THEN
LIKELY NOT TO RECOVER MUCH TODAY...WITH THE AFTERNOON IN THE MID
20S TO LOWER 30S FOR MOST. STEEP LOW-LEVEL LAPSE RATES BEHIND
THIS FRONT ARE ASSISTING IN WIDESPREAD FLURRIES ENTERING NORTHERN
ILLINOIS PER RADAR AND OBSERVATIONS...WITH A SCATTERING OF
EMBEDDED HIGHER REFLECTIVITY AND MORE SNOW SHOWER-ISH ACTIVITY.
AM EXPECTING THIS TO BASICALLY BE THE CASE TODAY ACROSS OUR
AREA...THAT IS FLURRIES MORE OFTEN THAN NOT...WITH OCCASIONAL TRUE
SNOW SHOWERS AND QUICKLY VARYING VISIBILITY. THE COVERAGE OF SNOW
SHOWERS WILL BE MODULATED BY A HANDFUL OF FACTORS...WITH VORTICITY
MAXIMAS PROBABLY THE SIMPLEST TO KEY IN ON...WITH OTHERS BEING
MORE MESOSCALE /E.G. LOW-LEVEL F-GEN/. THESE FACTORS WITHIN SOME
OF THE HIGH-RES HOURLY GUIDANCE THROUGH TODAY WOULD POINT TOWARD
SLIGHTLY BETTER TRUE SNOW SHOWER COVERAGE OVER THE WESTERN AND
SOUTHERN CWA. BUT AGAIN TOUGH TO TIME EXACTLY SO A BROAD
CONSISTENT FORECAST MESSAGE FOR TODAY.

STRONGER SYNOPTIC LIFT...SLIGHTLY BETTER LAPSE RATES...AND A MORE
FAVORABLE THERMAL PROFILE FOR DENDRITES ALL ARRIVE EARLY THIS
EVENING FROM NORTH TO SOUTH AS A VORTICITY LOBE ROTATES
SOUTHWARD. THE MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH
THIS AND HAVE JUST GONE LIGHT SNOW AREAWIDE. THIS FOR NORTHERN
AREAS WILL LIKELY OVERLAP AT LEAST PART OF THE EVENING COMMUTE
AND A PERSISTENT...THOUGH LIGHT...ACCUMULATION IS LIKELY TO BEGIN
IN THAT TIME. ITS MORE CHALLENGING TO SAY WHEN THIS PERIOD WILL
END...BUT IT LOOKS TO CONTINUE INTO TUESDAY MORNING. WITH
NORTHWEST LOW-LEVEL WINDS HAVING INCREASED ON RE-ENFORCED COLD
ADVECTION...VISIBILITY COULD BE LOW TO QUITE LOW AT TIMES. SO WITH
POSSIBLE TWO COMMUTES LIKELY TO BE DEALING WITH LIGHT ACCUMULATING
SNOW AND SOME VARYING VISIBILITY HAVE GONE AHEAD AND ISSUED AN SPS
TO FURTHER THE MESSAGE.

LOW-LEVEL WINDS WILL TURN OFF THE LAKE IN NORTHWEST INDIANA WITH
LAKE ENHANCEMENT TO THE SNOW LIKELY INTO BOTH LAKE AND PORTER
COUNTY BY LATE TONIGHT...THOUGH THE LONGER FETCH WILL BE POINTED
INTO PORTER COUNTY. EQUILIBRIUM LEVELS ARE FORECAST TO BE AROUND
8000 FT THOUGH WITH A GRADUALLY DEEPENING DENDRITIC GROWTH LAYER.
SO THIS WILL HELP ACCUMULATIONS IN THIS AREA WITH 2 TO 3 INCHES
PRESENTLY FAVORED IN THE FAR NORTHEAST PART OF THE COUNTY BY
TUESDAY EVENING...AND ADDITIONAL AFTER THAT POINT LATE TUESDAY
NIGHT INTO WEDNESDAY...POSSIBLY EVEN A FEW MORE INCHES. WILL NEED
TO MONITOR IF A HEADLINE IS NEEDED...PARTICULARLY IF RATES ARE
MORE ENHANCED...ALTHOUGH THE BETTER LAKE EFFECT SETUP CONTINUES TO
LOOK FURTHER EAST...SO NOT ANTICIPATING IT AT THIS TIME.

TEMPERATURES LOOK TO NOT CLIMB AT ALL ON TUESDAY WITH WIND CHILLS
IN THE SINGLE DIGITS. CYCLONIC FLOW PERSISTS THROUGH WEDNESDAY SO
CONTINUE TO LEAN CLOUDIER THAN GUIDANCE INTO THEN. IF CLOUDS CAN
CLEAR BY WEDNESDAY NIGHT...THAT LOOKS TO BE A PARTICULARLY CHILLY
NIGHT WITH SOME OUTLYING AREAS POTENTIALLY DROPPING TO OR BELOW
ZERO.

MTF

&&

.LONG TERM...
340 AM CST

WEDNESDAY NIGHT THROUGH MONDAY...

THE PATTERN CONTINUES TO LOOK LIKE A COOLER THAN NORMAL ONE IN
THIS TIME PERIOD. THE ELEVATED BAROCLINIC ZONE ON THE WESTERN SIDE
OF THE EASTERN NORTH AMERICAN TROUGH LOOKS TO BE UNSETTLED WITH
SEVERAL RIPPLES SUPPORTING OCCASIONAL LIGHT SNOW
CHANCES...ALTHOUGH THE PLACEMENT OF THAT HAS LARGE SPREAD IN
GUIDANCE AT THIS TIME. AN EVEN MORE ANOMALOUS UPPER LEVEL LOW IS
FORECAST TO DIG INTO EASTERN CANADA BY FRIDAY OR SATURDAY...WITH
THE EC FURTHER SOUTH WITH THIS FEATURE. THIS RESULTS IN SOME
DIFFERENCES IN THE SURFACE PRESSURE FIELDS BETWEEN THE GFS AND
EC...THOUGH THE GENERAL SYNOPTIC PATTERN WITH A STRONG CANADIAN
HIGH TO THE WEST AND A STRONG COLD FRONT PUSHING SOUTH THROUGH THE
GREAT LAKES CAN SUPPORT BETTER LAKE EFFECT POTENTIAL FOR SOME OF
OUR LAKE ADJACENT AREAS...AT THIS TIME MORE SO FAR NORTHWEST
INDIANA. OVERALL THOUGH BECAUSE OF THE NORTHWEST FLOW...THE THREAT
OF WIDESPREAD HIGH IMPACT WEATHER LOOKS LOW AT THIS TIME.

MTF

&&

.AVIATION...
FOR THE 12Z TAFS...

MVFR CIGS ARE EXPECTED THROUGH THE PERIOD WITH BRIEF PERIODS OF
IFR PSBL EARLY THIS MORNING. VFR FLURRIES WILL BE AROUND
THROUGHOUT THE DAY. SCATTERED LIGHT TO MODERATE SNOW SHOWERS ARE
CURRENTLY ON RADAR AND THEY WILL CONTINUE THROUGH MID MORNING. THE
HEAVIEST SNOW SHOWERS WILL BRING VSBY DOWN TO BELOW 1SM AND
PRODUCE A QUICK DUSTING OF SNOW. ONLY A COUPLE TENTHS OF AN INCH
OF SNOW ARE EXPECTED THROUGH THIS AFTN.

MORE STEADY SNOW IS EXPECTED THIS EVENING INTO TUESDAY MORNING
WITH IFR OR LOWER VSBY. ACCUMULATING SNOW IS EXPECTED WITH TOTALS
OF 1-2 INCHES BY TUESDAY MORNING. GUSTY NORTHWEST WINDS ALSO
DEVELOP TONIGHT WITH GUSTS ARND 20 KT. THIS MAY RESULT IN BLOWING
SNOW AND CONTRIBUTE TO THE REDUCED VISIBILITIES.

HIGH CONFIDENCE IN SNOW AND SNOW TRENDS...CIGS...AND GUSTY WINDS.
MEDIUM CONFIDENCE IN HOW LOW VSBY WILL BE IN SNOW SHOWERS
OVERNIGHT...COULD BE LOWER THAN CURRENTLY FORECAST.

JEE

&&

.MARINE...
301 AM CST

ISSUED A SMALL CRAFT ADVISORY FOR TONIGHT THROUGH EARLY WEDNESDAY
NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY MORNING FOR
THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND WAVES.

A WEAK LOW OVER THE U.P. OF MI WILL DRIFT OVER THE LAKE TODAY AND
REACH THE EASTERN GREAT LAKES LATE THIS AFTERNOON.  WINDS WILL
BECOME NORTH BEHIND THE LOW AND INCREASE TO 30 KT.  HIGH PRESSURE
SINKS SOUTH OVER THE PLAINS TUESDAY NIGHT AND MOVES OVER THE
MISSISSIPPI VALLEY WEDNESDAY EVENING. THE TIGHTENED GRADIENT BETWEEN
THE HIGH AND LOW WILL RESULT IN AN EXTENDED PERIOD OF 30 KT WINDS
THROUGH WEDNESDAY NIGHT. LOW END GALE FORCE GUSTS ARE POSSIBLE LATE
TUESDAY AFTERNOON OVER THE NORTHERN HALF OF THE LAKE...AND THE GALES
REACH THE SOUTHERN END OF THE LAKE TUESDAY NIGHT.  HOWEVER...DO NOT
HAVE ENOUGH CONFIDENCE IN GALES TO ISSUE A GALE WATCH FOR TUESDAY
NIGHT INTO WEDNESDAY.  WINDS DIMINISH AS THE HIGH MOVES OVER THE
LAKE WEDNESDAY NIGHT INTO THURSDAY.

ANOTHER WEAK LOW PASSES OVER THE EASTERN GREAT LAKES THURSDAY NIGHT
AND FRIDAY WHILE HIGH PRESSURE MOVES OVER MINNESOTA FRIDAY NIGHT AND
SATURDAY.  NORTHWEST TO NORTH WINDS INCREASE TO 30 KT LATE IN THE
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 081141
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
541 AM CST MON FEB 8 2016

.SHORT TERM...
337 AM CST

THROUGH WEDNESDAY...

THE FORECAST DETAILS AND OVERALL MESSAGE REMAIN SIMILAR FOR THE
UPCOMING LONG DURATION LIGHT SNOW EVENT WITHIN A MORE BLUSTERY
AND COLDER PATTERN. HAVE HONED FURTHER IN ON THIS EVENING THROUGH
TUESDAY MORNING AS A PROBABLE TIME FOR WIDESPREAD LIGHT SNOW WITH
ACCUMULATIONS...WITH TODAY SEEING MORE FLURRIES AND OCCASIONAL
SNOW SHOWERS. WITH THE OVER 30 HOURS EXPECTED OF OFF AND ON
SNOW...ACCUMULATIONS CONTINUE TO LOOK ON THE ORDER OF ONE HALF TO
2.5 INCHES FOR MOST AREAS. IN GENERAL...HIGHER TOTALS LOOK
EAST...ALTHOUGH SNOWFALL TOTALS TEND TO END UP LIKE A WRINKLED
SHEET AND NOT NICE AND SMOOTH /BORROWED THAT FROM A COLLEAGUE/.
FINALLY...PORTER COUNTY INDIANA STILL LOOKS TO HAVE LAKE EFFECT
ENHANCEMENT THAT WILL BRING SNOWFALL TOTALS UP.

ONE OF THE MORE PRONOUNCED COLD CORE UPPER LOWS OF THIS WINTER IS
ROTATING ITS WAY SOUTHEASTWARD ACROSS THE WESTERN GREAT LAKES
EARLY THIS MORNING. LARGE SCALE WATER VAPOR IMAGERY REVEALS THE
UPPER JET MAXIMUM IS STILL ROUNDING THE TOP OF THE WESTERN NORTH
AMERICAN RIDGE WITH THE RIDGE CONTINUING TO BUILD. AS A
RESULT...THE GREAT LAKES TROUGH WILL CONTINUE TO DIG AND PROGRESS
SOUTHEAST THROUGH TONIGHT AS THAT JET HEADS DUE SOUTH OVER THE
PLAINS. IN ADDITION...THE DEEP LOW OFF THE EASTERN SEABOARD WILL
FURTHER KEEP OUR UPPER LOW FROM PROGRESSING QUICKLY
EAST...ASSISTING IN THE BUILDING CHILL AND LONG DURATION LIGHT
SNOW.

THE PRIMARY SURFACE COLD FRONT WILL CLEAR THE AREA SOON AFTER
DAYBREAK WITH TEMPERATURES INCHING DOWNWARD A FEW DEGREES AND THEN
LIKELY NOT TO RECOVER MUCH TODAY...WITH THE AFTERNOON IN THE MID
20S TO LOWER 30S FOR MOST. STEEP LOW-LEVEL LAPSE RATES BEHIND
THIS FRONT ARE ASSISTING IN WIDESPREAD FLURRIES ENTERING NORTHERN
ILLINOIS PER RADAR AND OBSERVATIONS...WITH A SCATTERING OF
EMBEDDED HIGHER REFLECTIVITY AND MORE SNOW SHOWER-ISH ACTIVITY.
AM EXPECTING THIS TO BASICALLY BE THE CASE TODAY ACROSS OUR
AREA...THAT IS FLURRIES MORE OFTEN THAN NOT...WITH OCCASIONAL TRUE
SNOW SHOWERS AND QUICKLY VARYING VISIBILITY. THE COVERAGE OF SNOW
SHOWERS WILL BE MODULATED BY A HANDFUL OF FACTORS...WITH VORTICITY
MAXIMAS PROBABLY THE SIMPLEST TO KEY IN ON...WITH OTHERS BEING
MORE MESOSCALE /E.G. LOW-LEVEL F-GEN/. THESE FACTORS WITHIN SOME
OF THE HIGH-RES HOURLY GUIDANCE THROUGH TODAY WOULD POINT TOWARD
SLIGHTLY BETTER TRUE SNOW SHOWER COVERAGE OVER THE WESTERN AND
SOUTHERN CWA. BUT AGAIN TOUGH TO TIME EXACTLY SO A BROAD
CONSISTENT FORECAST MESSAGE FOR TODAY.

STRONGER SYNOPTIC LIFT...SLIGHTLY BETTER LAPSE RATES...AND A MORE
FAVORABLE THERMAL PROFILE FOR DENDRITES ALL ARRIVE EARLY THIS
EVENING FROM NORTH TO SOUTH AS A VORTICITY LOBE ROTATES
SOUTHWARD. THE MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH
THIS AND HAVE JUST GONE LIGHT SNOW AREAWIDE. THIS FOR NORTHERN
AREAS WILL LIKELY OVERLAP AT LEAST PART OF THE EVENING COMMUTE
AND A PERSISTENT...THOUGH LIGHT...ACCUMULATION IS LIKELY TO BEGIN
IN THAT TIME. ITS MORE CHALLENGING TO SAY WHEN THIS PERIOD WILL
END...BUT IT LOOKS TO CONTINUE INTO TUESDAY MORNING. WITH
NORTHWEST LOW-LEVEL WINDS HAVING INCREASED ON RE-ENFORCED COLD
ADVECTION...VISIBILITY COULD BE LOW TO QUITE LOW AT TIMES. SO WITH
POSSIBLE TWO COMMUTES LIKELY TO BE DEALING WITH LIGHT ACCUMULATING
SNOW AND SOME VARYING VISIBILITY HAVE GONE AHEAD AND ISSUED AN SPS
TO FURTHER THE MESSAGE.

LOW-LEVEL WINDS WILL TURN OFF THE LAKE IN NORTHWEST INDIANA WITH
LAKE ENHANCEMENT TO THE SNOW LIKELY INTO BOTH LAKE AND PORTER
COUNTY BY LATE TONIGHT...THOUGH THE LONGER FETCH WILL BE POINTED
INTO PORTER COUNTY. EQUILIBRIUM LEVELS ARE FORECAST TO BE AROUND
8000 FT THOUGH WITH A GRADUALLY DEEPENING DENDRITIC GROWTH LAYER.
SO THIS WILL HELP ACCUMULATIONS IN THIS AREA WITH 2 TO 3 INCHES
PRESENTLY FAVORED IN THE FAR NORTHEAST PART OF THE COUNTY BY
TUESDAY EVENING...AND ADDITIONAL AFTER THAT POINT LATE TUESDAY
NIGHT INTO WEDNESDAY...POSSIBLY EVEN A FEW MORE INCHES. WILL NEED
TO MONITOR IF A HEADLINE IS NEEDED...PARTICULARLY IF RATES ARE
MORE ENHANCED...ALTHOUGH THE BETTER LAKE EFFECT SETUP CONTINUES TO
LOOK FURTHER EAST...SO NOT ANTICIPATING IT AT THIS TIME.

TEMPERATURES LOOK TO NOT CLIMB AT ALL ON TUESDAY WITH WIND CHILLS
IN THE SINGLE DIGITS. CYCLONIC FLOW PERSISTS THROUGH WEDNESDAY SO
CONTINUE TO LEAN CLOUDIER THAN GUIDANCE INTO THEN. IF CLOUDS CAN
CLEAR BY WEDNESDAY NIGHT...THAT LOOKS TO BE A PARTICULARLY CHILLY
NIGHT WITH SOME OUTLYING AREAS POTENTIALLY DROPPING TO OR BELOW
ZERO.

MTF

&&

.LONG TERM...
340 AM CST

WEDNESDAY NIGHT THROUGH MONDAY...

THE PATTERN CONTINUES TO LOOK LIKE A COOLER THAN NORMAL ONE IN
THIS TIME PERIOD. THE ELEVATED BAROCLINIC ZONE ON THE WESTERN SIDE
OF THE EASTERN NORTH AMERICAN TROUGH LOOKS TO BE UNSETTLED WITH
SEVERAL RIPPLES SUPPORTING OCCASIONAL LIGHT SNOW
CHANCES...ALTHOUGH THE PLACEMENT OF THAT HAS LARGE SPREAD IN
GUIDANCE AT THIS TIME. AN EVEN MORE ANOMALOUS UPPER LEVEL LOW IS
FORECAST TO DIG INTO EASTERN CANADA BY FRIDAY OR SATURDAY...WITH
THE EC FURTHER SOUTH WITH THIS FEATURE. THIS RESULTS IN SOME
DIFFERENCES IN THE SURFACE PRESSURE FIELDS BETWEEN THE GFS AND
EC...THOUGH THE GENERAL SYNOPTIC PATTERN WITH A STRONG CANADIAN
HIGH TO THE WEST AND A STRONG COLD FRONT PUSHING SOUTH THROUGH THE
GREAT LAKES CAN SUPPORT BETTER LAKE EFFECT POTENTIAL FOR SOME OF
OUR LAKE ADJACENT AREAS...AT THIS TIME MORE SO FAR NORTHWEST
INDIANA. OVERALL THOUGH BECAUSE OF THE NORTHWEST FLOW...THE THREAT
OF WIDESPREAD HIGH IMPACT WEATHER LOOKS LOW AT THIS TIME.

MTF

&&

.AVIATION...
FOR THE 12Z TAFS...

MVFR CIGS ARE EXPECTED THROUGH THE PERIOD WITH BRIEF PERIODS OF
IFR PSBL EARLY THIS MORNING. VFR FLURRIES WILL BE AROUND
THROUGHOUT THE DAY. SCATTERED LIGHT TO MODERATE SNOW SHOWERS ARE
CURRENTLY ON RADAR AND THEY WILL CONTINUE THROUGH MID MORNING. THE
HEAVIEST SNOW SHOWERS WILL BRING VSBY DOWN TO BELOW 1SM AND
PRODUCE A QUICK DUSTING OF SNOW. ONLY A COUPLE TENTHS OF AN INCH
OF SNOW ARE EXPECTED THROUGH THIS AFTN.

MORE STEADY SNOW IS EXPECTED THIS EVENING INTO TUESDAY MORNING
WITH IFR OR LOWER VSBY. ACCUMULATING SNOW IS EXPECTED WITH TOTALS
OF 1-2 INCHES BY TUESDAY MORNING. GUSTY NORTHWEST WINDS ALSO
DEVELOP TONIGHT WITH GUSTS ARND 20 KT. THIS MAY RESULT IN BLOWING
SNOW AND CONTRIBUTE TO THE REDUCED VISIBILITIES.

HIGH CONFIDENCE IN SNOW AND SNOW TRENDS...CIGS...AND GUSTY WINDS.
MEDIUM CONFIDENCE IN HOW LOW VSBY WILL BE IN SNOW SHOWERS
OVERNIGHT...COULD BE LOWER THAN CURRENTLY FORECAST.

JEE

&&

.MARINE...
301 AM CST

ISSUED A SMALL CRAFT ADVISORY FOR TONIGHT THROUGH EARLY WEDNESDAY
NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY MORNING FOR
THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND WAVES.

A WEAK LOW OVER THE U.P. OF MI WILL DRIFT OVER THE LAKE TODAY AND
REACH THE EASTERN GREAT LAKES LATE THIS AFTERNOON.  WINDS WILL
BECOME NORTH BEHIND THE LOW AND INCREASE TO 30 KT.  HIGH PRESSURE
SINKS SOUTH OVER THE PLAINS TUESDAY NIGHT AND MOVES OVER THE
MISSISSIPPI VALLEY WEDNESDAY EVENING. THE TIGHTENED GRADIENT BETWEEN
THE HIGH AND LOW WILL RESULT IN AN EXTENDED PERIOD OF 30 KT WINDS
THROUGH WEDNESDAY NIGHT. LOW END GALE FORCE GUSTS ARE POSSIBLE LATE
TUESDAY AFTERNOON OVER THE NORTHERN HALF OF THE LAKE...AND THE GALES
REACH THE SOUTHERN END OF THE LAKE TUESDAY NIGHT.  HOWEVER...DO NOT
HAVE ENOUGH CONFIDENCE IN GALES TO ISSUE A GALE WATCH FOR TUESDAY
NIGHT INTO WEDNESDAY.  WINDS DIMINISH AS THE HIGH MOVES OVER THE
LAKE WEDNESDAY NIGHT INTO THURSDAY.

ANOTHER WEAK LOW PASSES OVER THE EASTERN GREAT LAKES THURSDAY NIGHT
AND FRIDAY WHILE HIGH PRESSURE MOVES OVER MINNESOTA FRIDAY NIGHT AND
SATURDAY.  NORTHWEST TO NORTH WINDS INCREASE TO 30 KT LATE IN THE
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 081141
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
541 AM CST MON FEB 8 2016

.SHORT TERM...
337 AM CST

THROUGH WEDNESDAY...

THE FORECAST DETAILS AND OVERALL MESSAGE REMAIN SIMILAR FOR THE
UPCOMING LONG DURATION LIGHT SNOW EVENT WITHIN A MORE BLUSTERY
AND COLDER PATTERN. HAVE HONED FURTHER IN ON THIS EVENING THROUGH
TUESDAY MORNING AS A PROBABLE TIME FOR WIDESPREAD LIGHT SNOW WITH
ACCUMULATIONS...WITH TODAY SEEING MORE FLURRIES AND OCCASIONAL
SNOW SHOWERS. WITH THE OVER 30 HOURS EXPECTED OF OFF AND ON
SNOW...ACCUMULATIONS CONTINUE TO LOOK ON THE ORDER OF ONE HALF TO
2.5 INCHES FOR MOST AREAS. IN GENERAL...HIGHER TOTALS LOOK
EAST...ALTHOUGH SNOWFALL TOTALS TEND TO END UP LIKE A WRINKLED
SHEET AND NOT NICE AND SMOOTH /BORROWED THAT FROM A COLLEAGUE/.
FINALLY...PORTER COUNTY INDIANA STILL LOOKS TO HAVE LAKE EFFECT
ENHANCEMENT THAT WILL BRING SNOWFALL TOTALS UP.

ONE OF THE MORE PRONOUNCED COLD CORE UPPER LOWS OF THIS WINTER IS
ROTATING ITS WAY SOUTHEASTWARD ACROSS THE WESTERN GREAT LAKES
EARLY THIS MORNING. LARGE SCALE WATER VAPOR IMAGERY REVEALS THE
UPPER JET MAXIMUM IS STILL ROUNDING THE TOP OF THE WESTERN NORTH
AMERICAN RIDGE WITH THE RIDGE CONTINUING TO BUILD. AS A
RESULT...THE GREAT LAKES TROUGH WILL CONTINUE TO DIG AND PROGRESS
SOUTHEAST THROUGH TONIGHT AS THAT JET HEADS DUE SOUTH OVER THE
PLAINS. IN ADDITION...THE DEEP LOW OFF THE EASTERN SEABOARD WILL
FURTHER KEEP OUR UPPER LOW FROM PROGRESSING QUICKLY
EAST...ASSISTING IN THE BUILDING CHILL AND LONG DURATION LIGHT
SNOW.

THE PRIMARY SURFACE COLD FRONT WILL CLEAR THE AREA SOON AFTER
DAYBREAK WITH TEMPERATURES INCHING DOWNWARD A FEW DEGREES AND THEN
LIKELY NOT TO RECOVER MUCH TODAY...WITH THE AFTERNOON IN THE MID
20S TO LOWER 30S FOR MOST. STEEP LOW-LEVEL LAPSE RATES BEHIND
THIS FRONT ARE ASSISTING IN WIDESPREAD FLURRIES ENTERING NORTHERN
ILLINOIS PER RADAR AND OBSERVATIONS...WITH A SCATTERING OF
EMBEDDED HIGHER REFLECTIVITY AND MORE SNOW SHOWER-ISH ACTIVITY.
AM EXPECTING THIS TO BASICALLY BE THE CASE TODAY ACROSS OUR
AREA...THAT IS FLURRIES MORE OFTEN THAN NOT...WITH OCCASIONAL TRUE
SNOW SHOWERS AND QUICKLY VARYING VISIBILITY. THE COVERAGE OF SNOW
SHOWERS WILL BE MODULATED BY A HANDFUL OF FACTORS...WITH VORTICITY
MAXIMAS PROBABLY THE SIMPLEST TO KEY IN ON...WITH OTHERS BEING
MORE MESOSCALE /E.G. LOW-LEVEL F-GEN/. THESE FACTORS WITHIN SOME
OF THE HIGH-RES HOURLY GUIDANCE THROUGH TODAY WOULD POINT TOWARD
SLIGHTLY BETTER TRUE SNOW SHOWER COVERAGE OVER THE WESTERN AND
SOUTHERN CWA. BUT AGAIN TOUGH TO TIME EXACTLY SO A BROAD
CONSISTENT FORECAST MESSAGE FOR TODAY.

STRONGER SYNOPTIC LIFT...SLIGHTLY BETTER LAPSE RATES...AND A MORE
FAVORABLE THERMAL PROFILE FOR DENDRITES ALL ARRIVE EARLY THIS
EVENING FROM NORTH TO SOUTH AS A VORTICITY LOBE ROTATES
SOUTHWARD. THE MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH
THIS AND HAVE JUST GONE LIGHT SNOW AREAWIDE. THIS FOR NORTHERN
AREAS WILL LIKELY OVERLAP AT LEAST PART OF THE EVENING COMMUTE
AND A PERSISTENT...THOUGH LIGHT...ACCUMULATION IS LIKELY TO BEGIN
IN THAT TIME. ITS MORE CHALLENGING TO SAY WHEN THIS PERIOD WILL
END...BUT IT LOOKS TO CONTINUE INTO TUESDAY MORNING. WITH
NORTHWEST LOW-LEVEL WINDS HAVING INCREASED ON RE-ENFORCED COLD
ADVECTION...VISIBILITY COULD BE LOW TO QUITE LOW AT TIMES. SO WITH
POSSIBLE TWO COMMUTES LIKELY TO BE DEALING WITH LIGHT ACCUMULATING
SNOW AND SOME VARYING VISIBILITY HAVE GONE AHEAD AND ISSUED AN SPS
TO FURTHER THE MESSAGE.

LOW-LEVEL WINDS WILL TURN OFF THE LAKE IN NORTHWEST INDIANA WITH
LAKE ENHANCEMENT TO THE SNOW LIKELY INTO BOTH LAKE AND PORTER
COUNTY BY LATE TONIGHT...THOUGH THE LONGER FETCH WILL BE POINTED
INTO PORTER COUNTY. EQUILIBRIUM LEVELS ARE FORECAST TO BE AROUND
8000 FT THOUGH WITH A GRADUALLY DEEPENING DENDRITIC GROWTH LAYER.
SO THIS WILL HELP ACCUMULATIONS IN THIS AREA WITH 2 TO 3 INCHES
PRESENTLY FAVORED IN THE FAR NORTHEAST PART OF THE COUNTY BY
TUESDAY EVENING...AND ADDITIONAL AFTER THAT POINT LATE TUESDAY
NIGHT INTO WEDNESDAY...POSSIBLY EVEN A FEW MORE INCHES. WILL NEED
TO MONITOR IF A HEADLINE IS NEEDED...PARTICULARLY IF RATES ARE
MORE ENHANCED...ALTHOUGH THE BETTER LAKE EFFECT SETUP CONTINUES TO
LOOK FURTHER EAST...SO NOT ANTICIPATING IT AT THIS TIME.

TEMPERATURES LOOK TO NOT CLIMB AT ALL ON TUESDAY WITH WIND CHILLS
IN THE SINGLE DIGITS. CYCLONIC FLOW PERSISTS THROUGH WEDNESDAY SO
CONTINUE TO LEAN CLOUDIER THAN GUIDANCE INTO THEN. IF CLOUDS CAN
CLEAR BY WEDNESDAY NIGHT...THAT LOOKS TO BE A PARTICULARLY CHILLY
NIGHT WITH SOME OUTLYING AREAS POTENTIALLY DROPPING TO OR BELOW
ZERO.

MTF

&&

.LONG TERM...
340 AM CST

WEDNESDAY NIGHT THROUGH MONDAY...

THE PATTERN CONTINUES TO LOOK LIKE A COOLER THAN NORMAL ONE IN
THIS TIME PERIOD. THE ELEVATED BAROCLINIC ZONE ON THE WESTERN SIDE
OF THE EASTERN NORTH AMERICAN TROUGH LOOKS TO BE UNSETTLED WITH
SEVERAL RIPPLES SUPPORTING OCCASIONAL LIGHT SNOW
CHANCES...ALTHOUGH THE PLACEMENT OF THAT HAS LARGE SPREAD IN
GUIDANCE AT THIS TIME. AN EVEN MORE ANOMALOUS UPPER LEVEL LOW IS
FORECAST TO DIG INTO EASTERN CANADA BY FRIDAY OR SATURDAY...WITH
THE EC FURTHER SOUTH WITH THIS FEATURE. THIS RESULTS IN SOME
DIFFERENCES IN THE SURFACE PRESSURE FIELDS BETWEEN THE GFS AND
EC...THOUGH THE GENERAL SYNOPTIC PATTERN WITH A STRONG CANADIAN
HIGH TO THE WEST AND A STRONG COLD FRONT PUSHING SOUTH THROUGH THE
GREAT LAKES CAN SUPPORT BETTER LAKE EFFECT POTENTIAL FOR SOME OF
OUR LAKE ADJACENT AREAS...AT THIS TIME MORE SO FAR NORTHWEST
INDIANA. OVERALL THOUGH BECAUSE OF THE NORTHWEST FLOW...THE THREAT
OF WIDESPREAD HIGH IMPACT WEATHER LOOKS LOW AT THIS TIME.

MTF

&&

.AVIATION...
FOR THE 12Z TAFS...

MVFR CIGS ARE EXPECTED THROUGH THE PERIOD WITH BRIEF PERIODS OF
IFR PSBL EARLY THIS MORNING. VFR FLURRIES WILL BE AROUND
THROUGHOUT THE DAY. SCATTERED LIGHT TO MODERATE SNOW SHOWERS ARE
CURRENTLY ON RADAR AND THEY WILL CONTINUE THROUGH MID MORNING. THE
HEAVIEST SNOW SHOWERS WILL BRING VSBY DOWN TO BELOW 1SM AND
PRODUCE A QUICK DUSTING OF SNOW. ONLY A COUPLE TENTHS OF AN INCH
OF SNOW ARE EXPECTED THROUGH THIS AFTN.

MORE STEADY SNOW IS EXPECTED THIS EVENING INTO TUESDAY MORNING
WITH IFR OR LOWER VSBY. ACCUMULATING SNOW IS EXPECTED WITH TOTALS
OF 1-2 INCHES BY TUESDAY MORNING. GUSTY NORTHWEST WINDS ALSO
DEVELOP TONIGHT WITH GUSTS ARND 20 KT. THIS MAY RESULT IN BLOWING
SNOW AND CONTRIBUTE TO THE REDUCED VISIBILITIES.

HIGH CONFIDENCE IN SNOW AND SNOW TRENDS...CIGS...AND GUSTY WINDS.
MEDIUM CONFIDENCE IN HOW LOW VSBY WILL BE IN SNOW SHOWERS
OVERNIGHT...COULD BE LOWER THAN CURRENTLY FORECAST.

JEE

&&

.MARINE...
301 AM CST

ISSUED A SMALL CRAFT ADVISORY FOR TONIGHT THROUGH EARLY WEDNESDAY
NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY MORNING FOR
THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND WAVES.

A WEAK LOW OVER THE U.P. OF MI WILL DRIFT OVER THE LAKE TODAY AND
REACH THE EASTERN GREAT LAKES LATE THIS AFTERNOON.  WINDS WILL
BECOME NORTH BEHIND THE LOW AND INCREASE TO 30 KT.  HIGH PRESSURE
SINKS SOUTH OVER THE PLAINS TUESDAY NIGHT AND MOVES OVER THE
MISSISSIPPI VALLEY WEDNESDAY EVENING. THE TIGHTENED GRADIENT BETWEEN
THE HIGH AND LOW WILL RESULT IN AN EXTENDED PERIOD OF 30 KT WINDS
THROUGH WEDNESDAY NIGHT. LOW END GALE FORCE GUSTS ARE POSSIBLE LATE
TUESDAY AFTERNOON OVER THE NORTHERN HALF OF THE LAKE...AND THE GALES
REACH THE SOUTHERN END OF THE LAKE TUESDAY NIGHT.  HOWEVER...DO NOT
HAVE ENOUGH CONFIDENCE IN GALES TO ISSUE A GALE WATCH FOR TUESDAY
NIGHT INTO WEDNESDAY.  WINDS DIMINISH AS THE HIGH MOVES OVER THE
LAKE WEDNESDAY NIGHT INTO THURSDAY.

ANOTHER WEAK LOW PASSES OVER THE EASTERN GREAT LAKES THURSDAY NIGHT
AND FRIDAY WHILE HIGH PRESSURE MOVES OVER MINNESOTA FRIDAY NIGHT AND
SATURDAY.  NORTHWEST TO NORTH WINDS INCREASE TO 30 KT LATE IN THE
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 081141
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
541 AM CST MON FEB 8 2016

.SHORT TERM...
337 AM CST

THROUGH WEDNESDAY...

THE FORECAST DETAILS AND OVERALL MESSAGE REMAIN SIMILAR FOR THE
UPCOMING LONG DURATION LIGHT SNOW EVENT WITHIN A MORE BLUSTERY
AND COLDER PATTERN. HAVE HONED FURTHER IN ON THIS EVENING THROUGH
TUESDAY MORNING AS A PROBABLE TIME FOR WIDESPREAD LIGHT SNOW WITH
ACCUMULATIONS...WITH TODAY SEEING MORE FLURRIES AND OCCASIONAL
SNOW SHOWERS. WITH THE OVER 30 HOURS EXPECTED OF OFF AND ON
SNOW...ACCUMULATIONS CONTINUE TO LOOK ON THE ORDER OF ONE HALF TO
2.5 INCHES FOR MOST AREAS. IN GENERAL...HIGHER TOTALS LOOK
EAST...ALTHOUGH SNOWFALL TOTALS TEND TO END UP LIKE A WRINKLED
SHEET AND NOT NICE AND SMOOTH /BORROWED THAT FROM A COLLEAGUE/.
FINALLY...PORTER COUNTY INDIANA STILL LOOKS TO HAVE LAKE EFFECT
ENHANCEMENT THAT WILL BRING SNOWFALL TOTALS UP.

ONE OF THE MORE PRONOUNCED COLD CORE UPPER LOWS OF THIS WINTER IS
ROTATING ITS WAY SOUTHEASTWARD ACROSS THE WESTERN GREAT LAKES
EARLY THIS MORNING. LARGE SCALE WATER VAPOR IMAGERY REVEALS THE
UPPER JET MAXIMUM IS STILL ROUNDING THE TOP OF THE WESTERN NORTH
AMERICAN RIDGE WITH THE RIDGE CONTINUING TO BUILD. AS A
RESULT...THE GREAT LAKES TROUGH WILL CONTINUE TO DIG AND PROGRESS
SOUTHEAST THROUGH TONIGHT AS THAT JET HEADS DUE SOUTH OVER THE
PLAINS. IN ADDITION...THE DEEP LOW OFF THE EASTERN SEABOARD WILL
FURTHER KEEP OUR UPPER LOW FROM PROGRESSING QUICKLY
EAST...ASSISTING IN THE BUILDING CHILL AND LONG DURATION LIGHT
SNOW.

THE PRIMARY SURFACE COLD FRONT WILL CLEAR THE AREA SOON AFTER
DAYBREAK WITH TEMPERATURES INCHING DOWNWARD A FEW DEGREES AND THEN
LIKELY NOT TO RECOVER MUCH TODAY...WITH THE AFTERNOON IN THE MID
20S TO LOWER 30S FOR MOST. STEEP LOW-LEVEL LAPSE RATES BEHIND
THIS FRONT ARE ASSISTING IN WIDESPREAD FLURRIES ENTERING NORTHERN
ILLINOIS PER RADAR AND OBSERVATIONS...WITH A SCATTERING OF
EMBEDDED HIGHER REFLECTIVITY AND MORE SNOW SHOWER-ISH ACTIVITY.
AM EXPECTING THIS TO BASICALLY BE THE CASE TODAY ACROSS OUR
AREA...THAT IS FLURRIES MORE OFTEN THAN NOT...WITH OCCASIONAL TRUE
SNOW SHOWERS AND QUICKLY VARYING VISIBILITY. THE COVERAGE OF SNOW
SHOWERS WILL BE MODULATED BY A HANDFUL OF FACTORS...WITH VORTICITY
MAXIMAS PROBABLY THE SIMPLEST TO KEY IN ON...WITH OTHERS BEING
MORE MESOSCALE /E.G. LOW-LEVEL F-GEN/. THESE FACTORS WITHIN SOME
OF THE HIGH-RES HOURLY GUIDANCE THROUGH TODAY WOULD POINT TOWARD
SLIGHTLY BETTER TRUE SNOW SHOWER COVERAGE OVER THE WESTERN AND
SOUTHERN CWA. BUT AGAIN TOUGH TO TIME EXACTLY SO A BROAD
CONSISTENT FORECAST MESSAGE FOR TODAY.

STRONGER SYNOPTIC LIFT...SLIGHTLY BETTER LAPSE RATES...AND A MORE
FAVORABLE THERMAL PROFILE FOR DENDRITES ALL ARRIVE EARLY THIS
EVENING FROM NORTH TO SOUTH AS A VORTICITY LOBE ROTATES
SOUTHWARD. THE MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH
THIS AND HAVE JUST GONE LIGHT SNOW AREAWIDE. THIS FOR NORTHERN
AREAS WILL LIKELY OVERLAP AT LEAST PART OF THE EVENING COMMUTE
AND A PERSISTENT...THOUGH LIGHT...ACCUMULATION IS LIKELY TO BEGIN
IN THAT TIME. ITS MORE CHALLENGING TO SAY WHEN THIS PERIOD WILL
END...BUT IT LOOKS TO CONTINUE INTO TUESDAY MORNING. WITH
NORTHWEST LOW-LEVEL WINDS HAVING INCREASED ON RE-ENFORCED COLD
ADVECTION...VISIBILITY COULD BE LOW TO QUITE LOW AT TIMES. SO WITH
POSSIBLE TWO COMMUTES LIKELY TO BE DEALING WITH LIGHT ACCUMULATING
SNOW AND SOME VARYING VISIBILITY HAVE GONE AHEAD AND ISSUED AN SPS
TO FURTHER THE MESSAGE.

LOW-LEVEL WINDS WILL TURN OFF THE LAKE IN NORTHWEST INDIANA WITH
LAKE ENHANCEMENT TO THE SNOW LIKELY INTO BOTH LAKE AND PORTER
COUNTY BY LATE TONIGHT...THOUGH THE LONGER FETCH WILL BE POINTED
INTO PORTER COUNTY. EQUILIBRIUM LEVELS ARE FORECAST TO BE AROUND
8000 FT THOUGH WITH A GRADUALLY DEEPENING DENDRITIC GROWTH LAYER.
SO THIS WILL HELP ACCUMULATIONS IN THIS AREA WITH 2 TO 3 INCHES
PRESENTLY FAVORED IN THE FAR NORTHEAST PART OF THE COUNTY BY
TUESDAY EVENING...AND ADDITIONAL AFTER THAT POINT LATE TUESDAY
NIGHT INTO WEDNESDAY...POSSIBLY EVEN A FEW MORE INCHES. WILL NEED
TO MONITOR IF A HEADLINE IS NEEDED...PARTICULARLY IF RATES ARE
MORE ENHANCED...ALTHOUGH THE BETTER LAKE EFFECT SETUP CONTINUES TO
LOOK FURTHER EAST...SO NOT ANTICIPATING IT AT THIS TIME.

TEMPERATURES LOOK TO NOT CLIMB AT ALL ON TUESDAY WITH WIND CHILLS
IN THE SINGLE DIGITS. CYCLONIC FLOW PERSISTS THROUGH WEDNESDAY SO
CONTINUE TO LEAN CLOUDIER THAN GUIDANCE INTO THEN. IF CLOUDS CAN
CLEAR BY WEDNESDAY NIGHT...THAT LOOKS TO BE A PARTICULARLY CHILLY
NIGHT WITH SOME OUTLYING AREAS POTENTIALLY DROPPING TO OR BELOW
ZERO.

MTF

&&

.LONG TERM...
340 AM CST

WEDNESDAY NIGHT THROUGH MONDAY...

THE PATTERN CONTINUES TO LOOK LIKE A COOLER THAN NORMAL ONE IN
THIS TIME PERIOD. THE ELEVATED BAROCLINIC ZONE ON THE WESTERN SIDE
OF THE EASTERN NORTH AMERICAN TROUGH LOOKS TO BE UNSETTLED WITH
SEVERAL RIPPLES SUPPORTING OCCASIONAL LIGHT SNOW
CHANCES...ALTHOUGH THE PLACEMENT OF THAT HAS LARGE SPREAD IN
GUIDANCE AT THIS TIME. AN EVEN MORE ANOMALOUS UPPER LEVEL LOW IS
FORECAST TO DIG INTO EASTERN CANADA BY FRIDAY OR SATURDAY...WITH
THE EC FURTHER SOUTH WITH THIS FEATURE. THIS RESULTS IN SOME
DIFFERENCES IN THE SURFACE PRESSURE FIELDS BETWEEN THE GFS AND
EC...THOUGH THE GENERAL SYNOPTIC PATTERN WITH A STRONG CANADIAN
HIGH TO THE WEST AND A STRONG COLD FRONT PUSHING SOUTH THROUGH THE
GREAT LAKES CAN SUPPORT BETTER LAKE EFFECT POTENTIAL FOR SOME OF
OUR LAKE ADJACENT AREAS...AT THIS TIME MORE SO FAR NORTHWEST
INDIANA. OVERALL THOUGH BECAUSE OF THE NORTHWEST FLOW...THE THREAT
OF WIDESPREAD HIGH IMPACT WEATHER LOOKS LOW AT THIS TIME.

MTF

&&

.AVIATION...
FOR THE 12Z TAFS...

MVFR CIGS ARE EXPECTED THROUGH THE PERIOD WITH BRIEF PERIODS OF
IFR PSBL EARLY THIS MORNING. VFR FLURRIES WILL BE AROUND
THROUGHOUT THE DAY. SCATTERED LIGHT TO MODERATE SNOW SHOWERS ARE
CURRENTLY ON RADAR AND THEY WILL CONTINUE THROUGH MID MORNING. THE
HEAVIEST SNOW SHOWERS WILL BRING VSBY DOWN TO BELOW 1SM AND
PRODUCE A QUICK DUSTING OF SNOW. ONLY A COUPLE TENTHS OF AN INCH
OF SNOW ARE EXPECTED THROUGH THIS AFTN.

MORE STEADY SNOW IS EXPECTED THIS EVENING INTO TUESDAY MORNING
WITH IFR OR LOWER VSBY. ACCUMULATING SNOW IS EXPECTED WITH TOTALS
OF 1-2 INCHES BY TUESDAY MORNING. GUSTY NORTHWEST WINDS ALSO
DEVELOP TONIGHT WITH GUSTS ARND 20 KT. THIS MAY RESULT IN BLOWING
SNOW AND CONTRIBUTE TO THE REDUCED VISIBILITIES.

HIGH CONFIDENCE IN SNOW AND SNOW TRENDS...CIGS...AND GUSTY WINDS.
MEDIUM CONFIDENCE IN HOW LOW VSBY WILL BE IN SNOW SHOWERS
OVERNIGHT...COULD BE LOWER THAN CURRENTLY FORECAST.

JEE

&&

.MARINE...
301 AM CST

ISSUED A SMALL CRAFT ADVISORY FOR TONIGHT THROUGH EARLY WEDNESDAY
NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY MORNING FOR
THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND WAVES.

A WEAK LOW OVER THE U.P. OF MI WILL DRIFT OVER THE LAKE TODAY AND
REACH THE EASTERN GREAT LAKES LATE THIS AFTERNOON.  WINDS WILL
BECOME NORTH BEHIND THE LOW AND INCREASE TO 30 KT.  HIGH PRESSURE
SINKS SOUTH OVER THE PLAINS TUESDAY NIGHT AND MOVES OVER THE
MISSISSIPPI VALLEY WEDNESDAY EVENING. THE TIGHTENED GRADIENT BETWEEN
THE HIGH AND LOW WILL RESULT IN AN EXTENDED PERIOD OF 30 KT WINDS
THROUGH WEDNESDAY NIGHT. LOW END GALE FORCE GUSTS ARE POSSIBLE LATE
TUESDAY AFTERNOON OVER THE NORTHERN HALF OF THE LAKE...AND THE GALES
REACH THE SOUTHERN END OF THE LAKE TUESDAY NIGHT.  HOWEVER...DO NOT
HAVE ENOUGH CONFIDENCE IN GALES TO ISSUE A GALE WATCH FOR TUESDAY
NIGHT INTO WEDNESDAY.  WINDS DIMINISH AS THE HIGH MOVES OVER THE
LAKE WEDNESDAY NIGHT INTO THURSDAY.

ANOTHER WEAK LOW PASSES OVER THE EASTERN GREAT LAKES THURSDAY NIGHT
AND FRIDAY WHILE HIGH PRESSURE MOVES OVER MINNESOTA FRIDAY NIGHT AND
SATURDAY.  NORTHWEST TO NORTH WINDS INCREASE TO 30 KT LATE IN THE
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 080946
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
346 AM CST MON FEB 8 2016

.SHORT TERM...
337 AM CST

THROUGH WEDNESDAY...

THE FORECAST DETAILS AND OVERALL MESSAGE REMAIN SIMILAR FOR THE
UPCOMING LONG DURATION LIGHT SNOW EVENT WITHIN A MORE BLUSTERY
AND COLDER PATTERN. HAVE HONED FURTHER IN ON THIS EVENING THROUGH
TUESDAY MORNING AS A PROBABLE TIME FOR WIDESPREAD LIGHT SNOW WITH
ACCUMULATIONS...WITH TODAY SEEING MORE FLURRIES AND OCCASIONAL
SNOW SHOWERS. WITH THE OVER 30 HOURS EXPECTED OF OFF AND ON
SNOW...ACCUMULATIONS CONTINUE TO LOOK ON THE ORDER OF ONE HALF TO
2.5 INCHES FOR MOST AREAS. IN GENERAL...HIGHER TOTALS LOOK
EAST...ALTHOUGH SNOWFALL TOTALS TEND TO END UP LIKE A WRINKLED
SHEET AND NOT NICE AND SMOOTH /BORROWED THAT FROM A COLLEAGUE/.
FINALLY...PORTER COUNTY INDIANA STILL LOOKS TO HAVE LAKE EFFECT
ENHANCEMENT THAT WILL BRING SNOWFALL TOTALS UP.

ONE OF THE MORE PRONOUNCED COLD CORE UPPER LOWS OF THIS WINTER IS
ROTATING ITS WAY SOUTHEASTWARD ACROSS THE WESTERN GREAT LAKES
EARLY THIS MORNING. LARGE SCALE WATER VAPOR IMAGERY REVEALS THE
UPPER JET MAXIMUM IS STILL ROUNDING THE TOP OF THE WESTERN NORTH
AMERICAN RIDGE WITH THE RIDGE CONTINUING TO BUILD. AS A
RESULT...THE GREAT LAKES TROUGH WILL CONTINUE TO DIG AND PROGRESS
SOUTHEAST THROUGH TONIGHT AS THAT JET HEADS DUE SOUTH OVER THE
PLAINS. IN ADDITION...THE DEEP LOW OFF THE EASTERN SEABOARD WILL
FURTHER KEEP OUR UPPER LOW FROM PROGRESSING QUICKLY
EAST...ASSISTING IN THE BUILDING CHILL AND LONG DURATION LIGHT
SNOW.

THE PRIMARY SURFACE COLD FRONT WILL CLEAR THE AREA SOON AFTER
DAYBREAK WITH TEMPERATURES INCHING DOWNWARD A FEW DEGREES AND THEN
LIKELY NOT TO RECOVER MUCH TODAY...WITH THE AFTERNOON IN THE MID
20S TO LOWER 30S FOR MOST. STEEP LOW-LEVEL LAPSE RATES BEHIND
THIS FRONT ARE ASSISTING IN WIDESPREAD FLURRIES ENTERING NORTHERN
ILLINOIS PER RADAR AND OBSERVATIONS...WITH A SCATTERING OF
EMBEDDED HIGHER REFLECTIVITY AND MORE SNOW SHOWER-ISH ACTIVITY.
AM EXPECTING THIS TO BASICALLY BE THE CASE TODAY ACROSS OUR
AREA...THAT IS FLURRIES MORE OFTEN THAN NOT...WITH OCCASIONAL TRUE
SNOW SHOWERS AND QUICKLY VARYING VISIBILITY. THE COVERAGE OF SNOW
SHOWERS WILL BE MODULATED BY A HANDFUL OF FACTORS...WITH VORTICITY
MAXIMAS PROBABLY THE SIMPLEST TO KEY IN ON...WITH OTHERS BEING
MORE MESOSCALE /E.G. LOW-LEVEL F-GEN/. THESE FACTORS WITHIN SOME
OF THE HIGH-RES HOURLY GUIDANCE THROUGH TODAY WOULD POINT TOWARD
SLIGHTLY BETTER TRUE SNOW SHOWER COVERAGE OVER THE WESTERN AND
SOUTHERN CWA. BUT AGAIN TOUGH TO TIME EXACTLY SO A BROAD
CONSISTENT FORECAST MESSAGE FOR TODAY.

STRONGER SYNOPTIC LIFT...SLIGHTLY BETTER LAPSE RATES...AND A MORE
FAVORABLE THERMAL PROFILE FOR DENDRITES ALL ARRIVE EARLY THIS
EVENING FROM NORTH TO SOUTH AS A VORTICITY LOBE ROTATES
SOUTHWARD. THE MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH
THIS AND HAVE JUST GONE LIGHT SNOW AREAWIDE. THIS FOR NORTHERN
AREAS WILL LIKELY OVERLAP AT LEAST PART OF THE EVENING COMMUTE
AND A PERSISTENT...THOUGH LIGHT...ACCUMULATION IS LIKELY TO BEGIN
IN THAT TIME. ITS MORE CHALLENGING TO SAY WHEN THIS PERIOD WILL
END...BUT IT LOOKS TO CONTINUE INTO TUESDAY MORNING. WITH
NORTHWEST LOW-LEVEL WINDS HAVING INCREASED ON RE-ENFORCED COLD
ADVECTION...VISIBILITY COULD BE LOW TO QUITE LOW AT TIMES. SO WITH
POSSIBLE TWO COMMUTES LIKELY TO BE DEALING WITH LIGHT ACCUMULATING
SNOW AND SOME VARYING VISIBILITY HAVE GONE AHEAD AND ISSUED AN SPS
TO FURTHER THE MESSAGE.

LOW-LEVEL WINDS WILL TURN OFF THE LAKE IN NORTHWEST INDIANA WITH
LAKE ENHANCEMENT TO THE SNOW LIKELY INTO BOTH LAKE AND PORTER
COUNTY BY LATE TONIGHT...THOUGH THE LONGER FETCH WILL BE POINTED
INTO PORTER COUNTY. EQUILIBRIUM LEVELS ARE FORECAST TO BE AROUND
8000 FT THOUGH WITH A GRADUALLY DEEPENING DENDRITIC GROWTH LAYER.
SO THIS WILL HELP ACCUMULATIONS IN THIS AREA WITH 2 TO 3 INCHES
PRESENTLY FAVORED IN THE FAR NORTHEAST PART OF THE COUNTY BY
TUESDAY EVENING...AND ADDITIONAL AFTER THAT POINT LATE TUESDAY
NIGHT INTO WEDNESDAY...POSSIBLY EVEN A FEW MORE INCHES. WILL NEED
TO MONITOR IF A HEADLINE IS NEEDED...PARTICULARLY IF RATES ARE
MORE ENHANCED...ALTHOUGH THE BETTER LAKE EFFECT SETUP CONTINUES TO
LOOK FURTHER EAST...SO NOT ANTICIPATING IT AT THIS TIME.

TEMPERATURES LOOK TO NOT CLIMB AT ALL ON TUESDAY WITH WIND CHILLS
IN THE SINGLE DIGITS. CYCLONIC FLOW PERSISTS THROUGH WEDNESDAY SO
CONTINUE TO LEAN CLOUDIER THAN GUIDANCE INTO THEN. IF CLOUDS CAN
CLEAR BY WEDNESDAY NIGHT...THAT LOOKS TO BE A PARTICULARLY CHILLY
NIGHT WITH SOME OUTLYING AREAS POTENTIALLY DROPPING TO OR BELOW
ZERO.

MTF

&&

.LONG TERM...
340 AM CST

WEDNESDAY NIGHT THROUGH MONDAY...

THE PATTERN CONTINUES TO LOOK LIKE A COOLER THAN NORMAL ONE IN
THIS TIME PERIOD. THE ELEVATED BAROCLINIC ZONE ON THE WESTERN SIDE
OF THE EASTERN NORTH AMERICAN TROUGH LOOKS TO BE UNSETTLED WITH
SEVERAL RIPPLES SUPPORTING OCCASIONAL LIGHT SNOW
CHANCES...ALTHOUGH THE PLACEMENT OF THAT HAS LARGE SPREAD IN
GUIDANCE AT THIS TIME. AN EVEN MORE ANOMALOUS UPPER LEVEL LOW IS
FORECAST TO DIG INTO EASTERN CANADA BY FRIDAY OR SATURDAY...WITH
THE EC FURTHER SOUTH WITH THIS FEATURE. THIS RESULTS IN SOME
DIFFERENCES IN THE SURFACE PRESSURE FIELDS BETWEEN THE GFS AND
EC...THOUGH THE GENERAL SYNOPTIC PATTERN WITH A STRONG CANADIAN
HIGH TO THE WEST AND A STRONG COLD FRONT PUSHING SOUTH THROUGH THE
GREAT LAKES CAN SUPPORT BETTER LAKE EFFECT POTENTIAL FOR SOME OF
OUR LAKE ADJACENT AREAS...AT THIS TIME MORE SO FAR NORTHWEST
INDIANA. OVERALL THOUGH BECAUSE OF THE NORTHWEST FLOW...THE THREAT
OF WIDESPREAD HIGH IMPACT WEATHER LOOKS LOW AT THIS TIME.

MTF

&&

.AVIATION...
FOR THE 06Z TAFS...

LIGHT REFLECTIVITIES CAN BE SEEN ON RADAR ALONG THE WESTERN IL AND
WI STATE LINES...WITH ONLY A FEW SITES REPORTING FLURRIES. THE
MORE WIDESPREAD SNOW IS ACROSS SOUTHEAST MN AND CENTRAL IOWA
ASSOCIATED WITH THE LOW/S VORTICITY STREAMER. GUIDANCE SUGGESTS
THAT IT WILL TAKE SOME TIME FOR THE COLUMN TO SATURATE AND SNOW TO
REACH THE GROUND...SO PUSHED BACK THE SNOW START TIME BY AN HOUR.
SNOW COULD TAKE EVEN LONGER TO START FALLING ESPECIALLY AT THE
EASTERN TERMINALS. SOME GUIDANCE MEMBERS SUGGEST SNOW WILL NOT
REACH THE GROUND UNTIL THIS EVENING...HOWEVER HAVE LOW CONFIDENCE
IN THOSE MEMBERS. FORCING FROM THE LOW WILL AT LEAST PRODUCE
FLURRIES THROUGHOUT THE DAY. A PERIOD OF MODERATE SNOW AND IFR
VSBY IS PSBL EARLY THIS MORNING. MVFR CIGS WILL ACCOMPANY THE SNOW
SHOWERS.

SOUTHWEST WINDS BECOME GUSTY NORTHWEST WINDS THIS EVENING.

HAVE HIGH CONFIDENCE IN MVFR CIGS AND SNOW FALLING FROM EARLY THIS
MORNING ONWARD. HAVE MEDIUM CONFIDENCE IN PERIODS OF MODERATE SNOW
AND IFR VSBY...BUT LOW CONFIDENCE IN EXACT TIMING. ALSO HAVE LOW
CONFIDENCE IN THE EXACT START TIME OF THE SNOW.

JEE

&&

.MARINE...
301 AM CST

ISSUED A SMALL CRAFT ADVISORY FOR TONIGHT THROUGH EARLY WEDNESDAY
NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY MORNING FOR
THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND WAVES.

A WEAK LOW OVER THE U.P. OF MI WILL DRIFT OVER THE LAKE TODAY AND
REACH THE EASTERN GREAT LAKES LATE THIS AFTERNOON.  WINDS WILL
BECOME NORTH BEHIND THE LOW AND INCREASE TO 30 KT.  HIGH PRESSURE
SINKS SOUTH OVER THE PLAINS TUESDAY NIGHT AND MOVES OVER THE
MISSISSIPPI VALLEY WEDNESDAY EVENING. THE TIGHTENED GRADIENT BETWEEN
THE HIGH AND LOW WILL RESULT IN AN EXTENDED PERIOD OF 30 KT WINDS
THROUGH WEDNESDAY NIGHT. LOW END GALE FORCE GUSTS ARE POSSIBLE LATE
TUESDAY AFTERNOON OVER THE NORTHERN HALF OF THE LAKE...AND THE GALES
REACH THE SOUTHERN END OF THE LAKE TUESDAY NIGHT.  HOWEVER...DO NOT
HAVE ENOUGH CONFIDENCE IN GALES TO ISSUE A GALE WATCH FOR TUESDAY
NIGHT INTO WEDNESDAY.  WINDS DIMINISH AS THE HIGH MOVES OVER THE
LAKE WEDNESDAY NIGHT INTO THURSDAY.

ANOTHER WEAK LOW PASSES OVER THE EASTERN GREAT LAKES THURSDAY NIGHT
AND FRIDAY WHILE HIGH PRESSURE MOVES OVER MINNESOTA FRIDAY NIGHT AND
SATURDAY.  NORTHWEST TO NORTH WINDS INCREASE TO 30 KT LATE IN THE
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 080902
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
302 AM CST MON FEB 8 2016

.UPDATE...
841 PM CST

NO BIG CHANGES NEEDED TO GOING FORECAST. AREA OF FLURRIES AND
EMBEDDED SNOW SHOWERS CONTINUES TO ADVANCE TO TOWARD THE AREA FROM
THE WEST AND NORTHWEST. LEADING EDGE IS SHOWING UP NICELY ONE KARX
WSR-88D WITH EXTRAPOLATION BRINGING THAT ACTIVITY INTO OUR FAR NW
CWA BY AROUND MIDNIGHT...SPREADING SOUTHEAST ACROSS THE REST OF
THE AREA OVERNIGHT. STEEP LOW-MID LEVEL LAPSE RATES AND
RESPECTABLE CONDITIONAL INSTABILITY SHOULD ALLOW FOR SOME EMBEDDED
HEAVIER SNOW SHOWERS...WHICH HAS ALREADY BEEN THE CASE UPSTREAM
WITH NUMEROUS AWOS/ASOS SITES DROPPING TO 1-2SM IN SHSN WITH ONE
OR TWO BRIEFLY DROPPING BELOW 1SM. TOUCHED UP THE PRECIP WORDING
BUT OTHERWISE MADE NO REAL CHANGES TO GOING FORECAST OTHER THAN
MINOR COSMETIC TIMING TWEAKS.

IZZI

&&

.SHORT TERM...
316 PM CST

TONIGHT THROUGH MONDAY...

MAIN FORECAST CONCERN IS WITH SNOW SHOWER ACTIVITY EXPECTED TO
OCCUR OVERNIGHT THROUGH MONDAY. LARGE VERTICALLY STACKED MID/UPPER
LOW CLEARLY NOTED ON AFTERNOON W/V IMAGERY WILL VERY GRADUALLY
SLIDE SOUTHEAST THROUGH THE PERIOD. SECONDARY COLD FRONT/THERMAL
TROUGH WILL PUSH ACROSS THE AREA OVERNIGHT. COLUMN WILL START OUT
QUITE DRY WHILE FORCING FROM UPPER LOW IS OVERHEAD THIS EVENING.
HOWEVER...WHEN BETTER SATURATION AND LOWERING OF CLOUDS OCCURS
LATE TONIGHT THROUGH THE OVERNIGHT...A SOMEWHAT SHEARED VORT MAX
ROTATING AROUND THE ULL WILL PIVOT ACROSS THE AREA. EXPECTING SNOW
SHOWER ACTIVITY TO BREAK OUT IN RESPONSE FROM NORTHWEST TO
SOUTHEAST. SETUP SHOULD ALSO FAVOR A NARROW MORE CONCENTRATED BAND
OF SNOW SHOWERS THAT WILL DEVELOP OVER THE AREA AND THEN MOVE
SOUTHEAST IN THE PREDAWN THROUGH EARLY MORNING HOURS. EXPERIMENTAL
HRRR HAS BEEN CONSISTENTLY DEPICTING THIS SCENARIO. STEEPENING LOW
LEVEL LAPSE RATES AND SOME 850 MB FGEN COULD POTENTIALLY YIELD
SOME BRIEFLY MODERATE SNOWFALL RATES AND VSBY REDUCTIONS BUT
OVERALL ACCUMS SHOULD BE MINIMAL AT BEST BY THE MONDAY MORNING
RUSH. IF THIS SNOW BAND DOES OCCUR...A FEW TENTHS COULD FALL.
TEMPERATURES ARE EXPECTED TO FALL INTO THE MID 20S TO AROUND 30 BY
DAYBREAK. WARM ROAD TEMPS FROM THE MILD WEEKEND SHOULD ALSO
PRECLUDE SIGNIFICANT TRAVEL IMPACTS.

DURING THE DAY ON MONDAY...IT`S CONCEIVABLE THAT THERE WILL BE NO
REAL BREAK IN THE FLURRIES AND SNOW SHOWERS AS BROAD SYNOPTIC LIFT
AND CAA REMAINS OVER THE AREA. HOWEVER...ASSESSING GUIDANCE...BEST
FOCUS FOR CONCENTRATED/POSSIBLY HEAVIER SNOW SHOWERS LOOKS TO BE
ASSOCIATED WITH A STRONG VORT MAX SHIFTING FROM NW IL AROUND 12Z
TO CENTRAL IL BY 18Z. INTRODUCED A SWATH OF CATEGORICAL POPS INTO
THE WESTERN AND SOUTHWEST CWA LATE AM THRU EARLY AFTERNOON. FOR
THE REST OF THE AREA...AS MENTIONED EARLIER...STUCK WITH LIKELY
POPS BUT COULD JUST BE FLURRIES/OCCASIONAL SNOW SHOWERS AND BRIEF
VSBY REDUCTIONS UNDER ANY STEADIER SNOW SHOWERS. TOTAL DAYTIME
SNOWFALL ACCUMULATIONS MAY BE UP TO A HALF INCH OR SO...BUT THERE
WILL LIKELY BE MORE VARIANCE THAN IS SHOWN IN OFFICIAL FORECAST.
ROAD IMPACTS...ESPECIALLY ON HEAVILY TRAVELED ROADS...WILL LIKELY
BE MITIGATED BY LINGERING SURFACE WARMTH FROM THE WEEKEND. GUSTY
WEST-N0RTHWEST WINDS...STRONGEST IN THE WESTERN HALF OF THE
CWA...COULD RESULT IN LOWER VSBY THAN FROM THE FALLING SNOW
ALONE. CLOUDS AND COLD AIR ADVECTION WILL NOT ENABLE TEMPERATURES
TO WARM MUCH FROM OVERNIGHT LOWS. ALL IN ALL...NOT EXPECTING
SIGNIFICANT IMPACTS FROM THE SNOW SHOWERS ON MONDAY...BUT LEAVE
SOME EXTRA TRAVEL TIME JUST IN CASE.

RC

&&

.LONG TERM...
241 PM CST

LONG TERM...

MONDAY NIGHT THROUGH SUNDAY...

FORECAST CONCERNS THROUGH THE EXTENDED PERIOD INCLUDE SNOW
SHOWERS ACROSS THE FORECAST AREA INTO WEDNESDAY...LAKE EFFECT SNOW
ACROSS PARTS OF NORTHWEST INDIANA...AND COLDER TEMPERATURES
THROUGH PERIOD.

DEEP CLOSED UPPER LOW DRIFTS SLOWLY SOUTHEAST FROM THE WESTERN
GREAT LAKES TO THE UPPER OHIO VALLEY THROUGH MID-WEEK...WITHIN
MASSIVE LARGE SCALE UPPER TROUGH ACROSS EASTERN NORTH AMERICA.
DEEP AND PERSISTENT NORTH-NORTHWESTERLY FLOW WEST OF THE TROUGH
AXIS PRODUCES AN INFLUX OF COLD ARCTIC AIR WITH 850 MB TEMPS
DROPPING INTO THE -15 TO -20 C RANGE AND WHICH LINGERS THROUGH
NEXT WEEKEND. STEEP LOW LEVEL LAPSE RATES AND A SERIES OF MID-
LEVEL VORTICITY MAXIMA WILL SET THE STAGE FOR PERIODIC SNOW
SHOWERS...ESPECIALLY FROM MONDAY NIGHT THROUGH EARLY WEDNESDAY
AFTER WHICH THE STRONG VORTICITY CHANNEL SHIFTS OFF TO THE EAST
AND MODELS INDICATE SUBSTANTIAL DRYING OF THE LOW-MID LEVELS BY
WEDNESDAY NIGHT. INTERMITTENT SNOW SHOWERS APPEAR FAIRLY LIKELY
WITHIN THIS REGIME ESPECIALLY EAST...WITH COVERAGE AND INTENSITY
MODULATED BY SMALLER AMPLITUDE SHORT WAVES/VORT MAXIMA ROTATING
THROUGH THE FLOW. WHILE LOW LEVEL LAPSE RATES AND INSTABILITY ARE
STRONGER MONDAY NIGHT...A STRONGER PUSH OF LOW LEVEL COLD AIR
ARRIVES TUESDAY WITH FORECAST SOUNDINGS FROM THE NAM/GFS/ECMWF ALL
INDICATING WEAK FORCING WITHIN A FAIRLY DEEP (200 MB) SATURATED
ISOTHERMAL PROFILE IN THE -10 TO -20 C DENDRITIC GROWTH ZONE FROM
EARLY TUESDAY MORNING INTO TUESDAY EVENING. THUS WHILE HIGHEST
POPS IN THE EXTENDED PERIOD ARE IN THE MONDAY NIGHT-EARLY TUESDAY
PERIOD...LIGHT ACCUMULATIONS WILL LIKELY CONTINUE INTO TUESDAY
AFTERNOON OR EVENING ACROSS THE EASTERN HALF OF THE CWA. MODEL QPF
GENERALLY RANGES FROM 0.05-0.10 INCHES MON NGT/TUESDAY... AND 0.05
INCHES OR LESS TUES NIGHT AND WEDNESDAY WITH LOWEST AMOUNTS
FARTHER WEST. SNOW TO LIQUID RATIOS INCREASING TO NEAR 20 TO 1
WOULD SUGGEST THE POTENTIAL FOR AS MUCH AS 2-3 INCHES OF
ACCUMULATION (OUTSIDE OF LAKE EFFECT AREAS) ACROSS THE EASTERN CWA
OVER ABOUT A 36 HOUR PERIOD...LESS TO THE WEST.

WITH COLD NORTH-NORTHWEST LOW LEVEL FLOW...THE LAKE SNOW BELT
REGION OF EASTERN LAKE AND PORTER COUNTIES WILL SEE LAKE EFFECT
SNOW DURING THE PERIOD...WITH THE FETCH FAVORABLE MAINLY EAST OF
GARY AS WINDS VEER MORE NORTHERLY. LAKE-INDUCED INSTABILITY RAMPS
UP QUICKLY DURING THE EVENING WITH EQUILIBRIUM LEVELS OF 8000-9000
FT...WEAKENING A BIT OVERNIGHT INTO TUESDAY AS LOW LEVELS COOL AND
STRENGTHEN INVERSION NEAR 850 MB. CONTINUED COOLING OF THE COLUMN
LEADS TO INCREASING INSTABILITY AGAIN LATER TUESDAY AFTERNOON INTO
WEDNESDAY...THOUGH GUIDANCE GENERALLY MAINTAINS THE STRONGEST LOW
LEVEL CONVERGENCE JUST EAST OF THE CWA FROM NORTHEAST PORTER INTO
LA PORTE AND BERRIEN COUNTIES. RISING MID-LEVEL HEIGHTS AND
SUBSIDENCE ALONG WITH WEAKENING FLOW/CONVERGENCE AND BACKING OF
LOW LEVEL WINDS TO A MORE WESTERLY DIRECTION SHOULD GRADUALLY
REDUCE ACCUMULATIONS WEDNESDAY AFTERNOON AND NIGHT. SEVERAL INCHES
OF ACCUMULATION DO APPEAR POSSIBLE BY THAT TIME MAINLY ACROSS
NORTHEAST PORTER COUNTY. LOW LEVEL WINDS EVENTUALLY BACK MORE
WESTERLY BY THURSDAY ENDING LIGHTER LAKE SNOW SHOWERS IN PORTER
COUNTY.

UPPER TROUGH SLOWLY DRIFTS EAST THROUGH THE END OF THE WEEK AND
NEXT WEEKEND...WITH SURFACE HIGH PRESSURE EVENTUALLY MOVING ACROSS
THE WESTERN LAKES LATE SATURDAY INTO SUNDAY. ARCTIC AIR WILL KEEP
TEMPERATURES BELOW NORMAL DURING THE TUESDAY-SUNDAY PERIOD HOWEVER
AS WE REMAIN IN NORTHWEST FLOW ALOFT BETWEEN EAST COAST TROUGH AND
DOWNSTREAM OF RIDGING ACROSS THE CENTRAL CONUS. TEMPS THROUGH THE
PERIOD GENERALLY EXPECTED TO SEE LOWS IN THE SINGLE DIGITS AND
HIGHS IN THE TEENS TO LOW 20S. SUB-ZERO MORNING WIND CHILLS ARE
EXPECTED PARTICULARLY WEDNESDAY AND THURSDAY MORNINGS.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

LIGHT REFLECTIVITIES CAN BE SEEN ON RADAR ALONG THE WESTERN IL AND
WI STATE LINES...WITH ONLY A FEW SITES REPORTING FLURRIES. THE
MORE WIDESPREAD SNOW IS ACROSS SOUTHEAST MN AND CENTRAL IOWA
ASSOCIATED WITH THE LOW/S VORTICITY STREAMER. GUIDANCE SUGGESTS
THAT IT WILL TAKE SOME TIME FOR THE COLUMN TO SATURATE AND SNOW TO
REACH THE GROUND...SO PUSHED BACK THE SNOW START TIME BY AN HOUR.
SNOW COULD TAKE EVEN LONGER TO START FALLING ESPECIALLY AT THE
EASTERN TERMINALS. SOME GUIDANCE MEMBERS SUGGEST SNOW WILL NOT
REACH THE GROUND UNTIL THIS EVENING...HOWEVER HAVE LOW CONFIDENCE
IN THOSE MEMBERS. FORCING FROM THE LOW WILL AT LEAST PRODUCE
FLURRIES THROUGHOUT THE DAY. A PERIOD OF MODERATE SNOW AND IFR
VSBY IS PSBL EARLY THIS MORNING. MVFR CIGS WILL ACCOMPANY THE SNOW
SHOWERS.

SOUTHWEST WINDS BECOME GUSTY NORTHWEST WINDS THIS EVENING.

HAVE HIGH CONFIDENCE IN MVFR CIGS AND SNOW FALLING FROM EARLY THIS
MORNING ONWARD. HAVE MEDIUM CONFIDENCE IN PERIODS OF MODERATE SNOW
AND IFR VSBY...BUT LOW CONFIDENCE IN EXACT TIMING. ALSO HAVE LOW
CONFIDENCE IN THE EXACT START TIME OF THE SNOW.

JEE

&&

.MARINE...
301 AM CST

ISSUED A SMALL CRAFT ADVISORY FOR TONIGHT THROUGH EARLY WEDNESDAY
NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY MORNING FOR
THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND WAVES.

A WEAK LOW OVER THE U.P. OF MI WILL DRIFT OVER THE LAKE TODAY AND
REACH THE EASTERN GREAT LAKES LATE THIS AFTERNOON.  WINDS WILL
BECOME NORTH BEHIND THE LOW AND INCREASE TO 30 KT.  HIGH PRESSURE
SINKS SOUTH OVER THE PLAINS TUESDAY NIGHT AND MOVES OVER THE
MISSISSIPPI VALLEY WEDNESDAY EVENING. THE TIGHTENED GRADIENT BETWEEN
THE HIGH AND LOW WILL RESULT IN AN EXTENDED PERIOD OF 30 KT WINDS
THROUGH WEDNESDAY NIGHT. LOW END GALE FORCE GUSTS ARE POSSIBLE LATE
TUESDAY AFTERNOON OVER THE NORTHERN HALF OF THE LAKE...AND THE GALES
REACH THE SOUTHERN END OF THE LAKE TUESDAY NIGHT.  HOWEVER...DO NOT
HAVE ENOUGH CONFIDENCE IN GALES TO ISSUE A GALE WATCH FOR TUESDAY
NIGHT INTO WEDNESDAY.  WINDS DIMINISH AS THE HIGH MOVES OVER THE
LAKE WEDNESDAY NIGHT INTO THURSDAY.

ANOTHER WEAK LOW PASSES OVER THE EASTERN GREAT LAKES THURSDAY NIGHT
AND FRIDAY WHILE HIGH PRESSURE MOVES OVER MINNESOTA FRIDAY NIGHT AND
SATURDAY.  NORTHWEST TO NORTH WINDS INCREASE TO 30 KT LATE IN THE
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 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 080525
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1125 PM CST SUN FEB 7 2016

.UPDATE...
841 PM CST

NO BIG CHANGES NEEDED TO GOING FORECAST. AREA OF FLURRIES AND
EMBEDDED SNOW SHOWERS CONTINUES TO ADVANCE TO TOWARD THE AREA FROM
THE WEST AND NORTHWEST. LEADING EDGE IS SHOWING UP NICELY ONE KARX
WSR-88D WITH EXTRAPOLATION BRINGING THAT ACTIVITY INTO OUR FAR NW
CWA BY AROUND MIDNIGHT...SPREADING SOUTHEAST ACROSS THE REST OF
THE AREA OVERNIGHT. STEEP LOW-MID LEVEL LAPSE RATES AND
RESPECTABLE CONDITIONAL INSTABILITY SHOULD ALLOW FOR SOME EMBEDDED
HEAVIER SNOW SHOWERS...WHICH HAS ALREADY BEEN THE CASE UPSTREAM
WITH NUMEROUS AWOS/ASOS SITES DROPPING TO 1-2SM IN SHSN WITH ONE
OR TWO BRIEFLY DROPPING BELOW 1SM. TOUCHED UP THE PRECIP WORDING
BUT OTHERWISE MADE NO REAL CHANGES TO GOING FORECAST OTHER THAN
MINOR COSMETIC TIMING TWEAKS.

IZZI

&&

.SHORT TERM...
316 PM CST

TONIGHT THROUGH MONDAY...

MAIN FORECAST CONCERN IS WITH SNOW SHOWER ACTIVITY EXPECTED TO
OCCUR OVERNIGHT THROUGH MONDAY. LARGE VERTICALLY STACKED MID/UPPER
LOW CLEARLY NOTED ON AFTERNOON W/V IMAGERY WILL VERY GRADUALLY
SLIDE SOUTHEAST THROUGH THE PERIOD. SECONDARY COLD FRONT/THERMAL
TROUGH WILL PUSH ACROSS THE AREA OVERNIGHT. COLUMN WILL START OUT
QUITE DRY WHILE FORCING FROM UPPER LOW IS OVERHEAD THIS EVENING.
HOWEVER...WHEN BETTER SATURATION AND LOWERING OF CLOUDS OCCURS
LATE TONIGHT THROUGH THE OVERNIGHT...A SOMEWHAT SHEARED VORT MAX
ROTATING AROUND THE ULL WILL PIVOT ACROSS THE AREA. EXPECTING SNOW
SHOWER ACTIVITY TO BREAK OUT IN RESPONSE FROM NORTHWEST TO
SOUTHEAST. SETUP SHOULD ALSO FAVOR A NARROW MORE CONCENTRATED BAND
OF SNOW SHOWERS THAT WILL DEVELOP OVER THE AREA AND THEN MOVE
SOUTHEAST IN THE PREDAWN THROUGH EARLY MORNING HOURS. EXPERIMENTAL
HRRR HAS BEEN CONSISTENTLY DEPICTING THIS SCENARIO. STEEPENING LOW
LEVEL LAPSE RATES AND SOME 850 MB FGEN COULD POTENTIALLY YIELD
SOME BRIEFLY MODERATE SNOWFALL RATES AND VSBY REDUCTIONS BUT
OVERALL ACCUMS SHOULD BE MINIMAL AT BEST BY THE MONDAY MORNING
RUSH. IF THIS SNOW BAND DOES OCCUR...A FEW TENTHS COULD FALL.
TEMPERATURES ARE EXPECTED TO FALL INTO THE MID 20S TO AROUND 30 BY
DAYBREAK. WARM ROAD TEMPS FROM THE MILD WEEKEND SHOULD ALSO
PRECLUDE SIGNIFICANT TRAVEL IMPACTS.

DURING THE DAY ON MONDAY...IT`S CONCEIVABLE THAT THERE WILL BE NO
REAL BREAK IN THE FLURRIES AND SNOW SHOWERS AS BROAD SYNOPTIC LIFT
AND CAA REMAINS OVER THE AREA. HOWEVER...ASSESSING GUIDANCE...BEST
FOCUS FOR CONCENTRATED/POSSIBLY HEAVIER SNOW SHOWERS LOOKS TO BE
ASSOCIATED WITH A STRONG VORT MAX SHIFTING FROM NW IL AROUND 12Z
TO CENTRAL IL BY 18Z. INTRODUCED A SWATH OF CATEGORICAL POPS INTO
THE WESTERN AND SOUTHWEST CWA LATE AM THRU EARLY AFTERNOON. FOR
THE REST OF THE AREA...AS MENTIONED EARLIER...STUCK WITH LIKELY
POPS BUT COULD JUST BE FLURRIES/OCCASIONAL SNOW SHOWERS AND BRIEF
VSBY REDUCTIONS UNDER ANY STEADIER SNOW SHOWERS. TOTAL DAYTIME
SNOWFALL ACCUMULATIONS MAY BE UP TO A HALF INCH OR SO...BUT THERE
WILL LIKELY BE MORE VARIANCE THAN IS SHOWN IN OFFICIAL FORECAST.
ROAD IMPACTS...ESPECIALLY ON HEAVILY TRAVELED ROADS...WILL LIKELY
BE MITIGATED BY LINGERING SURFACE WARMTH FROM THE WEEKEND. GUSTY
WEST-N0RTHWEST WINDS...STRONGEST IN THE WESTERN HALF OF THE
CWA...COULD RESULT IN LOWER VSBY THAN FROM THE FALLING SNOW
ALONE. CLOUDS AND COLD AIR ADVECTION WILL NOT ENABLE TEMPERATURES
TO WARM MUCH FROM OVERNIGHT LOWS. ALL IN ALL...NOT EXPECTING
SIGNIFICANT IMPACTS FROM THE SNOW SHOWERS ON MONDAY...BUT LEAVE
SOME EXTRA TRAVEL TIME JUST IN CASE.

RC

&&

.LONG TERM...
241 PM CST

LONG TERM...

MONDAY NIGHT THROUGH SUNDAY...

FORECAST CONCERNS THROUGH THE EXTENDED PERIOD INCLUDE SNOW
SHOWERS ACROSS THE FORECAST AREA INTO WEDNESDAY...LAKE EFFECT SNOW
ACROSS PARTS OF NORTHWEST INDIANA...AND COLDER TEMPERATURES
THROUGH PERIOD.

DEEP CLOSED UPPER LOW DRIFTS SLOWLY SOUTHEAST FROM THE WESTERN
GREAT LAKES TO THE UPPER OHIO VALLEY THROUGH MID-WEEK...WITHIN
MASSIVE LARGE SCALE UPPER TROUGH ACROSS EASTERN NORTH AMERICA.
DEEP AND PERSISTENT NORTH-NORTHWESTERLY FLOW WEST OF THE TROUGH
AXIS PRODUCES AN INFLUX OF COLD ARCTIC AIR WITH 850 MB TEMPS
DROPPING INTO THE -15 TO -20 C RANGE AND WHICH LINGERS THROUGH
NEXT WEEKEND. STEEP LOW LEVEL LAPSE RATES AND A SERIES OF MID-
LEVEL VORTICITY MAXIMA WILL SET THE STAGE FOR PERIODIC SNOW
SHOWERS...ESPECIALLY FROM MONDAY NIGHT THROUGH EARLY WEDNESDAY
AFTER WHICH THE STRONG VORTICITY CHANNEL SHIFTS OFF TO THE EAST
AND MODELS INDICATE SUBSTANTIAL DRYING OF THE LOW-MID LEVELS BY
WEDNESDAY NIGHT. INTERMITTENT SNOW SHOWERS APPEAR FAIRLY LIKELY
WITHIN THIS REGIME ESPECIALLY EAST...WITH COVERAGE AND INTENSITY
MODULATED BY SMALLER AMPLITUDE SHORT WAVES/VORT MAXIMA ROTATING
THROUGH THE FLOW. WHILE LOW LEVEL LAPSE RATES AND INSTABILITY ARE
STRONGER MONDAY NIGHT...A STRONGER PUSH OF LOW LEVEL COLD AIR
ARRIVES TUESDAY WITH FORECAST SOUNDINGS FROM THE NAM/GFS/ECMWF ALL
INDICATING WEAK FORCING WITHIN A FAIRLY DEEP (200 MB) SATURATED
ISOTHERMAL PROFILE IN THE -10 TO -20 C DENDRITIC GROWTH ZONE FROM
EARLY TUESDAY MORNING INTO TUESDAY EVENING. THUS WHILE HIGHEST
POPS IN THE EXTENDED PERIOD ARE IN THE MONDAY NIGHT-EARLY TUESDAY
PERIOD...LIGHT ACCUMULATIONS WILL LIKELY CONTINUE INTO TUESDAY
AFTERNOON OR EVENING ACROSS THE EASTERN HALF OF THE CWA. MODEL QPF
GENERALLY RANGES FROM 0.05-0.10 INCHES MON NGT/TUESDAY... AND 0.05
INCHES OR LESS TUES NIGHT AND WEDNESDAY WITH LOWEST AMOUNTS
FARTHER WEST. SNOW TO LIQUID RATIOS INCREASING TO NEAR 20 TO 1
WOULD SUGGEST THE POTENTIAL FOR AS MUCH AS 2-3 INCHES OF
ACCUMULATION (OUTSIDE OF LAKE EFFECT AREAS) ACROSS THE EASTERN CWA
OVER ABOUT A 36 HOUR PERIOD...LESS TO THE WEST.

WITH COLD NORTH-NORTHWEST LOW LEVEL FLOW...THE LAKE SNOW BELT
REGION OF EASTERN LAKE AND PORTER COUNTIES WILL SEE LAKE EFFECT
SNOW DURING THE PERIOD...WITH THE FETCH FAVORABLE MAINLY EAST OF
GARY AS WINDS VEER MORE NORTHERLY. LAKE-INDUCED INSTABILITY RAMPS
UP QUICKLY DURING THE EVENING WITH EQUILIBRIUM LEVELS OF 8000-9000
FT...WEAKENING A BIT OVERNIGHT INTO TUESDAY AS LOW LEVELS COOL AND
STRENGTHEN INVERSION NEAR 850 MB. CONTINUED COOLING OF THE COLUMN
LEADS TO INCREASING INSTABILITY AGAIN LATER TUESDAY AFTERNOON INTO
WEDNESDAY...THOUGH GUIDANCE GENERALLY MAINTAINS THE STRONGEST LOW
LEVEL CONVERGENCE JUST EAST OF THE CWA FROM NORTHEAST PORTER INTO
LA PORTE AND BERRIEN COUNTIES. RISING MID-LEVEL HEIGHTS AND
SUBSIDENCE ALONG WITH WEAKENING FLOW/CONVERGENCE AND BACKING OF
LOW LEVEL WINDS TO A MORE WESTERLY DIRECTION SHOULD GRADUALLY
REDUCE ACCUMULATIONS WEDNESDAY AFTERNOON AND NIGHT. SEVERAL INCHES
OF ACCUMULATION DO APPEAR POSSIBLE BY THAT TIME MAINLY ACROSS
NORTHEAST PORTER COUNTY. LOW LEVEL WINDS EVENTUALLY BACK MORE
WESTERLY BY THURSDAY ENDING LIGHTER LAKE SNOW SHOWERS IN PORTER
COUNTY.

UPPER TROUGH SLOWLY DRIFTS EAST THROUGH THE END OF THE WEEK AND
NEXT WEEKEND...WITH SURFACE HIGH PRESSURE EVENTUALLY MOVING ACROSS
THE WESTERN LAKES LATE SATURDAY INTO SUNDAY. ARCTIC AIR WILL KEEP
TEMPERATURES BELOW NORMAL DURING THE TUESDAY-SUNDAY PERIOD HOWEVER
AS WE REMAIN IN NORTHWEST FLOW ALOFT BETWEEN EAST COAST TROUGH AND
DOWNSTREAM OF RIDGING ACROSS THE CENTRAL CONUS. TEMPS THROUGH THE
PERIOD GENERALLY EXPECTED TO SEE LOWS IN THE SINGLE DIGITS AND
HIGHS IN THE TEENS TO LOW 20S. SUB-ZERO MORNING WIND CHILLS ARE
EXPECTED PARTICULARLY WEDNESDAY AND THURSDAY MORNINGS.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

LIGHT REFLECTIVITIES CAN BE SEEN ON RADAR ALONG THE WESTERN IL AND
WI STATE LINES...WITH ONLY A FEW SITES REPORTING FLURRIES. THE
MORE WIDESPREAD SNOW IS ACROSS SOUTHEAST MN AND CENTRAL IOWA
ASSOCIATED WITH THE LOW/S VORTICITY STREAMER. GUIDANCE SUGGESTS
THAT IT WILL TAKE SOME TIME FOR THE COLUMN TO SATURATE AND SNOW TO
REACH THE GROUND...SO PUSHED BACK THE SNOW START TIME BY AN HOUR.
SNOW COULD TAKE EVEN LONGER TO START FALLING ESPECIALLY AT THE
EASTERN TERMINALS. SOME GUIDANCE MEMBERS SUGGEST SNOW WILL NOT
REACH THE GROUND UNTIL THIS EVENING...HOWEVER HAVE LOW CONFIDENCE
IN THOSE MEMBERS. FORCING FROM THE LOW WILL AT LEAST PRODUCE
FLURRIES THROUGHOUT THE DAY. A PERIOD OF MODERATE SNOW AND IFR
VSBY IS PSBL EARLY THIS MORNING. MVFR CIGS WILL ACCOMPANY THE SNOW
SHOWERS.

SOUTHWEST WINDS BECOME GUSTY NORTHWEST WINDS THIS EVENING.

HAVE HIGH CONFIDENCE IN MVFR CIGS AND SNOW FALLING FROM EARLY THIS
MORNING ONWARD. HAVE MEDIUM CONFIDENCE IN PERIODS OF MODERATE SNOW
AND IFR VSBY...BUT LOW CONFIDENCE IN EXACT TIMING. ALSO HAVE LOW
CONFIDENCE IN THE EXACT START TIME OF THE SNOW.

JEE

&&

.MARINE...
309 PM CST

MAIN MARINE CONCERN IS WITH A PROLONGED PERIOD OF STRONG NORTH-
NORTHWEST WINDS DEVELOPING LATE MONDAY AND CONTINUING INTO MID-
WEEK.

LOW PRESSURE WAS OVER FAR WESTERN LAKE SUPERIOR THIS
AFTERNOON...AND THIS LOW WILL MOVE SOUTHEAST ACROSS LAKE ST CLAIR
BY EARLY MONDAY. A COLD FRONT WILL TRAIL THE LOW ACROSS LAKE
MICHIGAN TONIGHT...WITH A STRONGER SECONDARY COLD FRONT PUSHING
SOUTHEAST ACROSS THE LAKE ON MONDAY. COLD ARCTIC AIR WILL SPILL IN
FROM THE NORTHWEST BEHIND THIS SECOND COLD FRONT...WHICH COMBINED
WITH A STRONG PRESSURE GRADIENT WILL PRODUCE NORTH-NORTHWEST WINDS
AROUND 30 KT FROM MONDAY EVENING INTO WEDNESDAY AS THE LOWS
EASTWARD PROGRESSION IS SLOWED BY ANOTHER STORM OFF THE ATLANTIC
COAST. MARGINAL GALE FORCE GUSTS MAY OCCASIONALLY OCCUR DURING
THIS PERIOD...WITH FREEZING SPRAY LIKELY. HIGH PRESSURE RIDGING
WILL EVENTUALLY SPREAD SOUTHEAST FROM CENTRAL CANADA INTO THE
MISSISSIPPI VALLEY THURSDAY AND THURSDAY NIGHT...ALLOWING WINDS TO
EASE.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 080525
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1125 PM CST SUN FEB 7 2016

.UPDATE...
841 PM CST

NO BIG CHANGES NEEDED TO GOING FORECAST. AREA OF FLURRIES AND
EMBEDDED SNOW SHOWERS CONTINUES TO ADVANCE TO TOWARD THE AREA FROM
THE WEST AND NORTHWEST. LEADING EDGE IS SHOWING UP NICELY ONE KARX
WSR-88D WITH EXTRAPOLATION BRINGING THAT ACTIVITY INTO OUR FAR NW
CWA BY AROUND MIDNIGHT...SPREADING SOUTHEAST ACROSS THE REST OF
THE AREA OVERNIGHT. STEEP LOW-MID LEVEL LAPSE RATES AND
RESPECTABLE CONDITIONAL INSTABILITY SHOULD ALLOW FOR SOME EMBEDDED
HEAVIER SNOW SHOWERS...WHICH HAS ALREADY BEEN THE CASE UPSTREAM
WITH NUMEROUS AWOS/ASOS SITES DROPPING TO 1-2SM IN SHSN WITH ONE
OR TWO BRIEFLY DROPPING BELOW 1SM. TOUCHED UP THE PRECIP WORDING
BUT OTHERWISE MADE NO REAL CHANGES TO GOING FORECAST OTHER THAN
MINOR COSMETIC TIMING TWEAKS.

IZZI

&&

.SHORT TERM...
316 PM CST

TONIGHT THROUGH MONDAY...

MAIN FORECAST CONCERN IS WITH SNOW SHOWER ACTIVITY EXPECTED TO
OCCUR OVERNIGHT THROUGH MONDAY. LARGE VERTICALLY STACKED MID/UPPER
LOW CLEARLY NOTED ON AFTERNOON W/V IMAGERY WILL VERY GRADUALLY
SLIDE SOUTHEAST THROUGH THE PERIOD. SECONDARY COLD FRONT/THERMAL
TROUGH WILL PUSH ACROSS THE AREA OVERNIGHT. COLUMN WILL START OUT
QUITE DRY WHILE FORCING FROM UPPER LOW IS OVERHEAD THIS EVENING.
HOWEVER...WHEN BETTER SATURATION AND LOWERING OF CLOUDS OCCURS
LATE TONIGHT THROUGH THE OVERNIGHT...A SOMEWHAT SHEARED VORT MAX
ROTATING AROUND THE ULL WILL PIVOT ACROSS THE AREA. EXPECTING SNOW
SHOWER ACTIVITY TO BREAK OUT IN RESPONSE FROM NORTHWEST TO
SOUTHEAST. SETUP SHOULD ALSO FAVOR A NARROW MORE CONCENTRATED BAND
OF SNOW SHOWERS THAT WILL DEVELOP OVER THE AREA AND THEN MOVE
SOUTHEAST IN THE PREDAWN THROUGH EARLY MORNING HOURS. EXPERIMENTAL
HRRR HAS BEEN CONSISTENTLY DEPICTING THIS SCENARIO. STEEPENING LOW
LEVEL LAPSE RATES AND SOME 850 MB FGEN COULD POTENTIALLY YIELD
SOME BRIEFLY MODERATE SNOWFALL RATES AND VSBY REDUCTIONS BUT
OVERALL ACCUMS SHOULD BE MINIMAL AT BEST BY THE MONDAY MORNING
RUSH. IF THIS SNOW BAND DOES OCCUR...A FEW TENTHS COULD FALL.
TEMPERATURES ARE EXPECTED TO FALL INTO THE MID 20S TO AROUND 30 BY
DAYBREAK. WARM ROAD TEMPS FROM THE MILD WEEKEND SHOULD ALSO
PRECLUDE SIGNIFICANT TRAVEL IMPACTS.

DURING THE DAY ON MONDAY...IT`S CONCEIVABLE THAT THERE WILL BE NO
REAL BREAK IN THE FLURRIES AND SNOW SHOWERS AS BROAD SYNOPTIC LIFT
AND CAA REMAINS OVER THE AREA. HOWEVER...ASSESSING GUIDANCE...BEST
FOCUS FOR CONCENTRATED/POSSIBLY HEAVIER SNOW SHOWERS LOOKS TO BE
ASSOCIATED WITH A STRONG VORT MAX SHIFTING FROM NW IL AROUND 12Z
TO CENTRAL IL BY 18Z. INTRODUCED A SWATH OF CATEGORICAL POPS INTO
THE WESTERN AND SOUTHWEST CWA LATE AM THRU EARLY AFTERNOON. FOR
THE REST OF THE AREA...AS MENTIONED EARLIER...STUCK WITH LIKELY
POPS BUT COULD JUST BE FLURRIES/OCCASIONAL SNOW SHOWERS AND BRIEF
VSBY REDUCTIONS UNDER ANY STEADIER SNOW SHOWERS. TOTAL DAYTIME
SNOWFALL ACCUMULATIONS MAY BE UP TO A HALF INCH OR SO...BUT THERE
WILL LIKELY BE MORE VARIANCE THAN IS SHOWN IN OFFICIAL FORECAST.
ROAD IMPACTS...ESPECIALLY ON HEAVILY TRAVELED ROADS...WILL LIKELY
BE MITIGATED BY LINGERING SURFACE WARMTH FROM THE WEEKEND. GUSTY
WEST-N0RTHWEST WINDS...STRONGEST IN THE WESTERN HALF OF THE
CWA...COULD RESULT IN LOWER VSBY THAN FROM THE FALLING SNOW
ALONE. CLOUDS AND COLD AIR ADVECTION WILL NOT ENABLE TEMPERATURES
TO WARM MUCH FROM OVERNIGHT LOWS. ALL IN ALL...NOT EXPECTING
SIGNIFICANT IMPACTS FROM THE SNOW SHOWERS ON MONDAY...BUT LEAVE
SOME EXTRA TRAVEL TIME JUST IN CASE.

RC

&&

.LONG TERM...
241 PM CST

LONG TERM...

MONDAY NIGHT THROUGH SUNDAY...

FORECAST CONCERNS THROUGH THE EXTENDED PERIOD INCLUDE SNOW
SHOWERS ACROSS THE FORECAST AREA INTO WEDNESDAY...LAKE EFFECT SNOW
ACROSS PARTS OF NORTHWEST INDIANA...AND COLDER TEMPERATURES
THROUGH PERIOD.

DEEP CLOSED UPPER LOW DRIFTS SLOWLY SOUTHEAST FROM THE WESTERN
GREAT LAKES TO THE UPPER OHIO VALLEY THROUGH MID-WEEK...WITHIN
MASSIVE LARGE SCALE UPPER TROUGH ACROSS EASTERN NORTH AMERICA.
DEEP AND PERSISTENT NORTH-NORTHWESTERLY FLOW WEST OF THE TROUGH
AXIS PRODUCES AN INFLUX OF COLD ARCTIC AIR WITH 850 MB TEMPS
DROPPING INTO THE -15 TO -20 C RANGE AND WHICH LINGERS THROUGH
NEXT WEEKEND. STEEP LOW LEVEL LAPSE RATES AND A SERIES OF MID-
LEVEL VORTICITY MAXIMA WILL SET THE STAGE FOR PERIODIC SNOW
SHOWERS...ESPECIALLY FROM MONDAY NIGHT THROUGH EARLY WEDNESDAY
AFTER WHICH THE STRONG VORTICITY CHANNEL SHIFTS OFF TO THE EAST
AND MODELS INDICATE SUBSTANTIAL DRYING OF THE LOW-MID LEVELS BY
WEDNESDAY NIGHT. INTERMITTENT SNOW SHOWERS APPEAR FAIRLY LIKELY
WITHIN THIS REGIME ESPECIALLY EAST...WITH COVERAGE AND INTENSITY
MODULATED BY SMALLER AMPLITUDE SHORT WAVES/VORT MAXIMA ROTATING
THROUGH THE FLOW. WHILE LOW LEVEL LAPSE RATES AND INSTABILITY ARE
STRONGER MONDAY NIGHT...A STRONGER PUSH OF LOW LEVEL COLD AIR
ARRIVES TUESDAY WITH FORECAST SOUNDINGS FROM THE NAM/GFS/ECMWF ALL
INDICATING WEAK FORCING WITHIN A FAIRLY DEEP (200 MB) SATURATED
ISOTHERMAL PROFILE IN THE -10 TO -20 C DENDRITIC GROWTH ZONE FROM
EARLY TUESDAY MORNING INTO TUESDAY EVENING. THUS WHILE HIGHEST
POPS IN THE EXTENDED PERIOD ARE IN THE MONDAY NIGHT-EARLY TUESDAY
PERIOD...LIGHT ACCUMULATIONS WILL LIKELY CONTINUE INTO TUESDAY
AFTERNOON OR EVENING ACROSS THE EASTERN HALF OF THE CWA. MODEL QPF
GENERALLY RANGES FROM 0.05-0.10 INCHES MON NGT/TUESDAY... AND 0.05
INCHES OR LESS TUES NIGHT AND WEDNESDAY WITH LOWEST AMOUNTS
FARTHER WEST. SNOW TO LIQUID RATIOS INCREASING TO NEAR 20 TO 1
WOULD SUGGEST THE POTENTIAL FOR AS MUCH AS 2-3 INCHES OF
ACCUMULATION (OUTSIDE OF LAKE EFFECT AREAS) ACROSS THE EASTERN CWA
OVER ABOUT A 36 HOUR PERIOD...LESS TO THE WEST.

WITH COLD NORTH-NORTHWEST LOW LEVEL FLOW...THE LAKE SNOW BELT
REGION OF EASTERN LAKE AND PORTER COUNTIES WILL SEE LAKE EFFECT
SNOW DURING THE PERIOD...WITH THE FETCH FAVORABLE MAINLY EAST OF
GARY AS WINDS VEER MORE NORTHERLY. LAKE-INDUCED INSTABILITY RAMPS
UP QUICKLY DURING THE EVENING WITH EQUILIBRIUM LEVELS OF 8000-9000
FT...WEAKENING A BIT OVERNIGHT INTO TUESDAY AS LOW LEVELS COOL AND
STRENGTHEN INVERSION NEAR 850 MB. CONTINUED COOLING OF THE COLUMN
LEADS TO INCREASING INSTABILITY AGAIN LATER TUESDAY AFTERNOON INTO
WEDNESDAY...THOUGH GUIDANCE GENERALLY MAINTAINS THE STRONGEST LOW
LEVEL CONVERGENCE JUST EAST OF THE CWA FROM NORTHEAST PORTER INTO
LA PORTE AND BERRIEN COUNTIES. RISING MID-LEVEL HEIGHTS AND
SUBSIDENCE ALONG WITH WEAKENING FLOW/CONVERGENCE AND BACKING OF
LOW LEVEL WINDS TO A MORE WESTERLY DIRECTION SHOULD GRADUALLY
REDUCE ACCUMULATIONS WEDNESDAY AFTERNOON AND NIGHT. SEVERAL INCHES
OF ACCUMULATION DO APPEAR POSSIBLE BY THAT TIME MAINLY ACROSS
NORTHEAST PORTER COUNTY. LOW LEVEL WINDS EVENTUALLY BACK MORE
WESTERLY BY THURSDAY ENDING LIGHTER LAKE SNOW SHOWERS IN PORTER
COUNTY.

UPPER TROUGH SLOWLY DRIFTS EAST THROUGH THE END OF THE WEEK AND
NEXT WEEKEND...WITH SURFACE HIGH PRESSURE EVENTUALLY MOVING ACROSS
THE WESTERN LAKES LATE SATURDAY INTO SUNDAY. ARCTIC AIR WILL KEEP
TEMPERATURES BELOW NORMAL DURING THE TUESDAY-SUNDAY PERIOD HOWEVER
AS WE REMAIN IN NORTHWEST FLOW ALOFT BETWEEN EAST COAST TROUGH AND
DOWNSTREAM OF RIDGING ACROSS THE CENTRAL CONUS. TEMPS THROUGH THE
PERIOD GENERALLY EXPECTED TO SEE LOWS IN THE SINGLE DIGITS AND
HIGHS IN THE TEENS TO LOW 20S. SUB-ZERO MORNING WIND CHILLS ARE
EXPECTED PARTICULARLY WEDNESDAY AND THURSDAY MORNINGS.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

LIGHT REFLECTIVITIES CAN BE SEEN ON RADAR ALONG THE WESTERN IL AND
WI STATE LINES...WITH ONLY A FEW SITES REPORTING FLURRIES. THE
MORE WIDESPREAD SNOW IS ACROSS SOUTHEAST MN AND CENTRAL IOWA
ASSOCIATED WITH THE LOW/S VORTICITY STREAMER. GUIDANCE SUGGESTS
THAT IT WILL TAKE SOME TIME FOR THE COLUMN TO SATURATE AND SNOW TO
REACH THE GROUND...SO PUSHED BACK THE SNOW START TIME BY AN HOUR.
SNOW COULD TAKE EVEN LONGER TO START FALLING ESPECIALLY AT THE
EASTERN TERMINALS. SOME GUIDANCE MEMBERS SUGGEST SNOW WILL NOT
REACH THE GROUND UNTIL THIS EVENING...HOWEVER HAVE LOW CONFIDENCE
IN THOSE MEMBERS. FORCING FROM THE LOW WILL AT LEAST PRODUCE
FLURRIES THROUGHOUT THE DAY. A PERIOD OF MODERATE SNOW AND IFR
VSBY IS PSBL EARLY THIS MORNING. MVFR CIGS WILL ACCOMPANY THE SNOW
SHOWERS.

SOUTHWEST WINDS BECOME GUSTY NORTHWEST WINDS THIS EVENING.

HAVE HIGH CONFIDENCE IN MVFR CIGS AND SNOW FALLING FROM EARLY THIS
MORNING ONWARD. HAVE MEDIUM CONFIDENCE IN PERIODS OF MODERATE SNOW
AND IFR VSBY...BUT LOW CONFIDENCE IN EXACT TIMING. ALSO HAVE LOW
CONFIDENCE IN THE EXACT START TIME OF THE SNOW.

JEE

&&

.MARINE...
309 PM CST

MAIN MARINE CONCERN IS WITH A PROLONGED PERIOD OF STRONG NORTH-
NORTHWEST WINDS DEVELOPING LATE MONDAY AND CONTINUING INTO MID-
WEEK.

LOW PRESSURE WAS OVER FAR WESTERN LAKE SUPERIOR THIS
AFTERNOON...AND THIS LOW WILL MOVE SOUTHEAST ACROSS LAKE ST CLAIR
BY EARLY MONDAY. A COLD FRONT WILL TRAIL THE LOW ACROSS LAKE
MICHIGAN TONIGHT...WITH A STRONGER SECONDARY COLD FRONT PUSHING
SOUTHEAST ACROSS THE LAKE ON MONDAY. COLD ARCTIC AIR WILL SPILL IN
FROM THE NORTHWEST BEHIND THIS SECOND COLD FRONT...WHICH COMBINED
WITH A STRONG PRESSURE GRADIENT WILL PRODUCE NORTH-NORTHWEST WINDS
AROUND 30 KT FROM MONDAY EVENING INTO WEDNESDAY AS THE LOWS
EASTWARD PROGRESSION IS SLOWED BY ANOTHER STORM OFF THE ATLANTIC
COAST. MARGINAL GALE FORCE GUSTS MAY OCCASIONALLY OCCUR DURING
THIS PERIOD...WITH FREEZING SPRAY LIKELY. HIGH PRESSURE RIDGING
WILL EVENTUALLY SPREAD SOUTHEAST FROM CENTRAL CANADA INTO THE
MISSISSIPPI VALLEY THURSDAY AND THURSDAY NIGHT...ALLOWING WINDS TO
EASE.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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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