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000
FXUS65 KRIW 221003
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
303 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

CONDITIONS CONTINUE TO GENERALLY IMPROVE ACROSS THE AREA AS ALL
HIGHLIGHTS HAVE BEEN REMOVED. PERIODS OF LIGHT SNOWFALL WILL REMAIN
POSSIBLE THROUGH THE DAY ACROSS MUCH OF THE FORECAST AREA...THOUGH
SNOWFALL WILL MOST SIGNIFICANTLY IMPACT THE EASTERN THIRD OF THE
FORECAST AREA BY THIS AFTERNOON. TEMPERATURES ARE EXPECTED TO BE
COOLER TODAY IN RESPONSE TO THIS SYSTEM.

BUILDING HIGH PRESSURE OVER THE AREA WILL HELP TO END SNOWFALL
ACROSS THE WESTERN MOUNTAINS AND VALLEYS OVERNIGHT. SNOWFALL WILL
ALSO WANE ACROSS EASTERN WYOMING AS THE INFLUENCING SYSTEM MOVES
FURTHER INTO THE CENTRAL PLAINS.

HIGH PRESSURE ACROSS THE AREA WILL GENERALLY BE SHORT LIVED...THOUGH
GENERALLY DRY CONDITIONS WILL BE AROUND LATE TUESDAY THROUGH EARLY
WEDNESDAY. SLIGHTLY WARMER TEMPERATURES WILL BE REALIZED ON
WEDNESDAY AHEAD OF THE NEXT APPROACHING SYSTEM. MODELS TRY TO SHOW
SOME WEAK DISTURBANCES WITHIN THE RIDGE THAT WOULD CREATE SOME
SNOWFALL OVER THE NORTHWESTERN MOUNTAINS BY WEDNESDAY AFTERNOON.
COVERAGE DOES NOT APPEAR TO BECOME SIGNIFICANT UNTIL THE LATE
EVENING HOURS AS A TROUGH APPROACHES THE INTERMOUNTAIN WEST.

THIS TROUGH WILL WORK TO SPREAD SNOWFALL ACROSS THE WESTERN THIRD OF
THE FORECAST AREA THROUGH WEDNESDAY NIGHT.

.LONG TERM...CHRISTMAS DAY THURSDAY THROUGH MONDAY

THE MODELS CONTINUE TO ORDER UP A WHITE CHRISTMAS WITH SOME LIGHT
SNOW ACROSS MOST OF THE AREA DURING THE DAY INTO CHRISTMAS NIGHT.
ACCUMULATIONS AT THE LOWER ELEVATIONS 1 TO 3 INCHES AND 2 TO 5
NEW INCHES FOR THE MOUNTAINS. THE GFS AND ECMWF MODELS ARE STILL
TRENDING SLOWER WITH THE ONSET OF SNOW EAST OF THE DIVIDE...NOW
ACTUALLY LOOKING AT CHRISTMAS MORNING TO AS LATE AS MIDDAY. THE MAIN
CHANCE OF SNOW FOR SOME PLACES MAY OCCUR CHRISTMAS EVENING/NIGHT.
LINGERING LIGHT SNOW ON FRIDAY MORNING THEN MOSTLY DRY FRIDAY
AFTERNOON AND NIGHT EAST OF THE DIVIDE. MOUNTAINS COULD SEE LT SNOW
UNTIL LATE FRI PM OVER THE PEAKS AND PASSES. SATURDAY THROUGH
SATURDAY NIGHT LOOKS DRY EAST OF THE DIVIDE. IN THE WEST...SOME
MOISTURE MOVES BACK SATURDAY AFTERNOON AND NIGHT FOR AN INCREASING
CHANCE OF SNOW. THE NEXT WEATHER SYSTEM IS POISED TO MOVE INTO THE
ROCKY MOUNTAIN REGION SUNDAY THROUGH MONDAY. THIS SYSTEM TAPS SOME
ARCTIC AIR AND SENDS IT INTO WY SUNDAY NIGHT THROUGH MONDAY. LIGHT
FLUFFY SNOW WOULD ALSO OCCUR SUNDAY INTO MONDAY. PLENTY OF TIME TO
WATCH HOW MUCH COLD AIR GETS PULLED SOUTH AND ADJUST FORECAST WITH
TIME. BOTTOM LINE...AN UNSETTLED WEATHER PATTERN FROM CHRISTMAS DAY
INTO THE WEEKEND...IMPACTING TRAVEL FROM TIME TO TIME. HIGH TEMPS
WILL BE AT OR BELOW SEASONAL NORMALS THROUGH THE PERIOD.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE MONDAY AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS THE
CENTRAL BASINS.  SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH BACK
FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING MONDAY
NIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR WEST
AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
MONDAY AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO DIVE SOUTH ALONG THE DIVIDE LATE MONDAY MORNING AND
MONDAY AFTERNOON...EXITING SOUTH OF INTERSTATE 80 MONDAY EVENING.
SNOW SHOWER ACTIVITY WILL INCREASE AHEAD OF THIS SYSTEM FROM NW-SE
MONDAY MORNING WITH IMPROVING CONDITIONS AND GUSTY NW WINDS
FOLLOWING THE DISTURBANCE MONDAY AFTERNOON AND MONDAY EVENING.
CLEARING CONDITIONS AND DIMINISHING WIND WILL FOLLOW OVERNIGHT
MONDAY.

&&

.FIRE WEATHER...

GUSTY WIND WILL REMAIN ACROSS MUCH OF THE FORECAST AREA TODAY...WITH
WIND WEAKENING DURING THE EVENING AND OVERNIGHT HOURS. TEMPERATURES
WILL COOL ACROSS THE AREA TODAY...AND CONTINUE TO COOL TUESDAY
BEFORE EXPERIENCING A SLIGHT WARMING ON WEDNESDAY. SNOWFALL WILL
LINGER ACROSS THE AREA TODAY...WITH MUCH OF ITS IMPACT EXPECTED TO
BE FELT ACROSS THE EASTERN THIRD OF THE FORECAST AREA. HIGH PRESSURE
WILL MOVE IN THIS EVENING AND OVERNIGHT TO HELP END MOST SHOWER
ACTIVITY. THE NEXT APPROACHING TROUGH WILL MOVE INTO NORTHWESTERN
WYOMING WEDNESDAY AFTERNOON AND EVENING...AND WILL SPREAD THROUGH
THE OVERNIGHT HOURS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM










000
FXUS65 KRIW 221003
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
303 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

CONDITIONS CONTINUE TO GENERALLY IMPROVE ACROSS THE AREA AS ALL
HIGHLIGHTS HAVE BEEN REMOVED. PERIODS OF LIGHT SNOWFALL WILL REMAIN
POSSIBLE THROUGH THE DAY ACROSS MUCH OF THE FORECAST AREA...THOUGH
SNOWFALL WILL MOST SIGNIFICANTLY IMPACT THE EASTERN THIRD OF THE
FORECAST AREA BY THIS AFTERNOON. TEMPERATURES ARE EXPECTED TO BE
COOLER TODAY IN RESPONSE TO THIS SYSTEM.

BUILDING HIGH PRESSURE OVER THE AREA WILL HELP TO END SNOWFALL
ACROSS THE WESTERN MOUNTAINS AND VALLEYS OVERNIGHT. SNOWFALL WILL
ALSO WANE ACROSS EASTERN WYOMING AS THE INFLUENCING SYSTEM MOVES
FURTHER INTO THE CENTRAL PLAINS.

HIGH PRESSURE ACROSS THE AREA WILL GENERALLY BE SHORT LIVED...THOUGH
GENERALLY DRY CONDITIONS WILL BE AROUND LATE TUESDAY THROUGH EARLY
WEDNESDAY. SLIGHTLY WARMER TEMPERATURES WILL BE REALIZED ON
WEDNESDAY AHEAD OF THE NEXT APPROACHING SYSTEM. MODELS TRY TO SHOW
SOME WEAK DISTURBANCES WITHIN THE RIDGE THAT WOULD CREATE SOME
SNOWFALL OVER THE NORTHWESTERN MOUNTAINS BY WEDNESDAY AFTERNOON.
COVERAGE DOES NOT APPEAR TO BECOME SIGNIFICANT UNTIL THE LATE
EVENING HOURS AS A TROUGH APPROACHES THE INTERMOUNTAIN WEST.

THIS TROUGH WILL WORK TO SPREAD SNOWFALL ACROSS THE WESTERN THIRD OF
THE FORECAST AREA THROUGH WEDNESDAY NIGHT.

.LONG TERM...CHRISTMAS DAY THURSDAY THROUGH MONDAY

THE MODELS CONTINUE TO ORDER UP A WHITE CHRISTMAS WITH SOME LIGHT
SNOW ACROSS MOST OF THE AREA DURING THE DAY INTO CHRISTMAS NIGHT.
ACCUMULATIONS AT THE LOWER ELEVATIONS 1 TO 3 INCHES AND 2 TO 5
NEW INCHES FOR THE MOUNTAINS. THE GFS AND ECMWF MODELS ARE STILL
TRENDING SLOWER WITH THE ONSET OF SNOW EAST OF THE DIVIDE...NOW
ACTUALLY LOOKING AT CHRISTMAS MORNING TO AS LATE AS MIDDAY. THE MAIN
CHANCE OF SNOW FOR SOME PLACES MAY OCCUR CHRISTMAS EVENING/NIGHT.
LINGERING LIGHT SNOW ON FRIDAY MORNING THEN MOSTLY DRY FRIDAY
AFTERNOON AND NIGHT EAST OF THE DIVIDE. MOUNTAINS COULD SEE LT SNOW
UNTIL LATE FRI PM OVER THE PEAKS AND PASSES. SATURDAY THROUGH
SATURDAY NIGHT LOOKS DRY EAST OF THE DIVIDE. IN THE WEST...SOME
MOISTURE MOVES BACK SATURDAY AFTERNOON AND NIGHT FOR AN INCREASING
CHANCE OF SNOW. THE NEXT WEATHER SYSTEM IS POISED TO MOVE INTO THE
ROCKY MOUNTAIN REGION SUNDAY THROUGH MONDAY. THIS SYSTEM TAPS SOME
ARCTIC AIR AND SENDS IT INTO WY SUNDAY NIGHT THROUGH MONDAY. LIGHT
FLUFFY SNOW WOULD ALSO OCCUR SUNDAY INTO MONDAY. PLENTY OF TIME TO
WATCH HOW MUCH COLD AIR GETS PULLED SOUTH AND ADJUST FORECAST WITH
TIME. BOTTOM LINE...AN UNSETTLED WEATHER PATTERN FROM CHRISTMAS DAY
INTO THE WEEKEND...IMPACTING TRAVEL FROM TIME TO TIME. HIGH TEMPS
WILL BE AT OR BELOW SEASONAL NORMALS THROUGH THE PERIOD.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE MONDAY AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS THE
CENTRAL BASINS.  SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH BACK
FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING MONDAY
NIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR WEST
AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
MONDAY AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO DIVE SOUTH ALONG THE DIVIDE LATE MONDAY MORNING AND
MONDAY AFTERNOON...EXITING SOUTH OF INTERSTATE 80 MONDAY EVENING.
SNOW SHOWER ACTIVITY WILL INCREASE AHEAD OF THIS SYSTEM FROM NW-SE
MONDAY MORNING WITH IMPROVING CONDITIONS AND GUSTY NW WINDS
FOLLOWING THE DISTURBANCE MONDAY AFTERNOON AND MONDAY EVENING.
CLEARING CONDITIONS AND DIMINISHING WIND WILL FOLLOW OVERNIGHT
MONDAY.

&&

.FIRE WEATHER...

GUSTY WIND WILL REMAIN ACROSS MUCH OF THE FORECAST AREA TODAY...WITH
WIND WEAKENING DURING THE EVENING AND OVERNIGHT HOURS. TEMPERATURES
WILL COOL ACROSS THE AREA TODAY...AND CONTINUE TO COOL TUESDAY
BEFORE EXPERIENCING A SLIGHT WARMING ON WEDNESDAY. SNOWFALL WILL
LINGER ACROSS THE AREA TODAY...WITH MUCH OF ITS IMPACT EXPECTED TO
BE FELT ACROSS THE EASTERN THIRD OF THE FORECAST AREA. HIGH PRESSURE
WILL MOVE IN THIS EVENING AND OVERNIGHT TO HELP END MOST SHOWER
ACTIVITY. THE NEXT APPROACHING TROUGH WILL MOVE INTO NORTHWESTERN
WYOMING WEDNESDAY AFTERNOON AND EVENING...AND WILL SPREAD THROUGH
THE OVERNIGHT HOURS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM









000
FXUS65 KRIW 220640
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1140 PM MST SUN DEC 21 2014

.UPDATE...

CANCELLED REMAINING HIGH WIND WARNINGS FOR SOUTHERN
WYOMING...SO NO REMAINING WINTER STORM OR HIGH WIND WARNINGS ARE IN
EFFECT ACROSS THE CWA.

AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE MONDAY AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS THE
CENTRAL BASINS.  SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH BACK
FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING MONDAY
NIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR WEST
AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
MONDAY AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO DIVE SOUTH ALONG THE DIVIDE LATE MONDAY MORNING AND
MONDAY AFTERNOON...EXITING SOUTH OF INTERSTATE 80 MONDAY EVENING.
SNOW SHOWER ACTIVITY WILL INCREASE AHEAD OF THIS SYSTEM FROM NW-SE
MONDAY MORNING WITH IMPROVING CONDITIONS AND GUSTY NW WINDS
FOLLOWING THE DISTURBANCE MONDAY AFTERNOON AND MONDAY EVENING.
CLEARING CONDITIONS AND DIMINISHING WIND WILL FOLLOW OVERNIGHT
MONDAY.

&&

.PREV DISCUSSION... /ISSUED 304 PM MST SUN DEC 21 2014/

SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

UPDATE...AEM
SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...AEM
FIRE WEATHER...ALLEN










000
FXUS65 KRIW 220640
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1140 PM MST SUN DEC 21 2014

.UPDATE...

CANCELLED REMAINING HIGH WIND WARNINGS FOR SOUTHERN
WYOMING...SO NO REMAINING WINTER STORM OR HIGH WIND WARNINGS ARE IN
EFFECT ACROSS THE CWA.

AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE MONDAY AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS THE
CENTRAL BASINS.  SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH BACK
FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING MONDAY
NIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR WEST
AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
MONDAY AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO DIVE SOUTH ALONG THE DIVIDE LATE MONDAY MORNING AND
MONDAY AFTERNOON...EXITING SOUTH OF INTERSTATE 80 MONDAY EVENING.
SNOW SHOWER ACTIVITY WILL INCREASE AHEAD OF THIS SYSTEM FROM NW-SE
MONDAY MORNING WITH IMPROVING CONDITIONS AND GUSTY NW WINDS
FOLLOWING THE DISTURBANCE MONDAY AFTERNOON AND MONDAY EVENING.
CLEARING CONDITIONS AND DIMINISHING WIND WILL FOLLOW OVERNIGHT
MONDAY.

&&

.PREV DISCUSSION... /ISSUED 304 PM MST SUN DEC 21 2014/

SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

UPDATE...AEM
SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...AEM
FIRE WEATHER...ALLEN











000
FXUS65 KRIW 220424
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
924 PM MST SUN DEC 21 2014

.UPDATE...DRIER AIRMASS IN NW FLOW HAS PREVAILED ACROSS THE WEST
WITH LITTLE IN THE WAY OF ADDITIONAL SNOWFALL OVER THE LAST FEW
HOURS. CANCELLED ALL WINTER STORM WARNINGS ACROSS THE WEST. COLD
FRONT IS MOVING SOUTH ACROSS SOUTHERN WYOMING AND HAS SHUT OFF THE
WIND MACHINE ACROSS SOUTH PASS AND BEAVER RIM AREAS...SO HIGH WIND
WARNING HAS BEEN TAKEN DOWN THERE. LOCATIONS FURTHER SOUTH ARE
STILL BLOWING HIGH WIND OR NEAR HIGH WIND SO LET THE WARNINGS
CONTINUE...BUT COLD FRONT AND NW FLOW WILL SOON END THE EVENT
THERE AS WELL.

&&

.PREV DISCUSSION... /ISSUED 304 PM MST SUN DEC 21 2014/

SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

&&

$$

UPDATE...AEM
SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...ALLEN
FIRE WEATHER...ALLEN







000
FXUS65 KRIW 220424
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
924 PM MST SUN DEC 21 2014

.UPDATE...DRIER AIRMASS IN NW FLOW HAS PREVAILED ACROSS THE WEST
WITH LITTLE IN THE WAY OF ADDITIONAL SNOWFALL OVER THE LAST FEW
HOURS. CANCELLED ALL WINTER STORM WARNINGS ACROSS THE WEST. COLD
FRONT IS MOVING SOUTH ACROSS SOUTHERN WYOMING AND HAS SHUT OFF THE
WIND MACHINE ACROSS SOUTH PASS AND BEAVER RIM AREAS...SO HIGH WIND
WARNING HAS BEEN TAKEN DOWN THERE. LOCATIONS FURTHER SOUTH ARE
STILL BLOWING HIGH WIND OR NEAR HIGH WIND SO LET THE WARNINGS
CONTINUE...BUT COLD FRONT AND NW FLOW WILL SOON END THE EVENT
THERE AS WELL.

&&

.PREV DISCUSSION... /ISSUED 304 PM MST SUN DEC 21 2014/

SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

&&

$$

UPDATE...AEM
SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...ALLEN
FIRE WEATHER...ALLEN








000
FXUS65 KRIW 212204
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
304 PM MST SUN DEC 21 2014

.SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

.LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

&&

$$

SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...ALLEN
FIRE WEATHER...ALLEN







000
FXUS65 KRIW 212204
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
304 PM MST SUN DEC 21 2014

.SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

.LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

&&

$$

SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...ALLEN
FIRE WEATHER...ALLEN






000
FXUS65 KRIW 211757 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1057 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE BEGINNING TO MIX OUT BUT UNTIL THEN...EXPECT BRIEF PERIODS OF
LLWS AT FOOTHILL AND VALLEY TERMINALS FOLLOWED BY PERIODS OF 20 TO
30KT WINDS WITH GUSTS MAINLY IN THE 35-45KT RANGE BUT A FEW MORE
WIND PRONE AREAS COULD SEE GUSTS UP TO 60KT...BUT NOT AT ANY OF
THE FORECAST TERMINALS. A STRONG NW FLOW WILL FOLLOW THIS SYSTEM
TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG
THE FRONT ACROSS THE LOWER ELEVATIONS THIS EVENING...ESPECIALLY
VCNTY AND EAST OF INTERSTATE 25. DRIER AIR PREVAIL NW-SE BUT GUSTY
NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 00Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA THIS AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
AFTERNOON WYZ010.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
MORNING WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...ALLEN
FIRE WEATHER...BRANHAM






000
FXUS65 KRIW 211757 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1057 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE BEGINNING TO MIX OUT BUT UNTIL THEN...EXPECT BRIEF PERIODS OF
LLWS AT FOOTHILL AND VALLEY TERMINALS FOLLOWED BY PERIODS OF 20 TO
30KT WINDS WITH GUSTS MAINLY IN THE 35-45KT RANGE BUT A FEW MORE
WIND PRONE AREAS COULD SEE GUSTS UP TO 60KT...BUT NOT AT ANY OF
THE FORECAST TERMINALS. A STRONG NW FLOW WILL FOLLOW THIS SYSTEM
TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG
THE FRONT ACROSS THE LOWER ELEVATIONS THIS EVENING...ESPECIALLY
VCNTY AND EAST OF INTERSTATE 25. DRIER AIR PREVAIL NW-SE BUT GUSTY
NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 00Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA THIS AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
AFTERNOON WYZ010.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
MORNING WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...ALLEN
FIRE WEATHER...BRANHAM







000
FXUS65 KRIW 211010
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
310 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM THIS MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY AFTERNOON
WYZ010.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM









000
FXUS65 KRIW 211010
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
310 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM THIS MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY AFTERNOON
WYZ010.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM








000
FXUS65 KRIW 211010
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
310 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM THIS MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY AFTERNOON
WYZ010.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM









000
FXUS65 KRIW 211010
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
310 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM THIS MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY AFTERNOON
WYZ010.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM








000
FXUS65 KRIW 210624
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1124 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESSIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../06Z ISSUANCE/

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM SUNDAY MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.


&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STORM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...AEM
FIRE WEATHER...C.BAKER













000
FXUS65 KRIW 210624
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1124 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESSIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../06Z ISSUANCE/

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM SUNDAY MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.


&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STORM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...AEM
FIRE WEATHER...C.BAKER












000
FXUS65 KRIW 202225 CCA
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER










000
FXUS65 KRIW 202225 CCA
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER









000
FXUS65 KRIW 202149
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER






000
FXUS65 KRIW 202149
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER







000
FXUS65 KRIW 201728
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1028 AM MST SAT DEC 20 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

AN INTERESTING FORECAST PERIOD WITH A LOT OF POTENTIALLY
SIGNIFICANT WEATHER DEVELOPING. A NEARLY ZONAL FLOW PATTERN IS
EXPECTED THIS MORNING AND AFTERNOON...WITH SOME MOISTURE INCREASE
SNOWFALL COVERAGE A BIT ACROSS WESTERN WYOMING.

A PACIFIC STORM SYSTEM WILL CONTINUE TO MOVE THROUGH THE
INTERMOUNTAIN WEST SATURDAY EVENING...WITH SNOWFALL INCREASING
ACROSS WESTERN WYOMING. ADDITIONALLY...AN INCREASED TEMPERATURE
GRADIENT IS EXPECTED BETWEEN CODY AND THE EASTERN PORTION OF
YELLOWSTONE NATIONAL PARK. ADDITIONAL MOUNTAIN WAVE SIGNATURES ARE
BEING DEMONSTRATED IN CURRENT MODEL ANALYSIS...WITH VERY STRONG
WIND POSSIBLE AROUND THE FAVORED CLARK AREA. A HIGH WIND WATCH IS
IN EFFECT FOR THIS LOCATION.

SNOWFALL IS EXPECTED TO INCREASE TONIGHT AND PERSIST THROUGH
MONDAY MORNING. SNOWFALL IS LOOKING TO BECOME HEAVY AT TIMES WITH
SIGNIFICANT ACCUMULATIONS POSSIBLE ACROSS THE WESTERN MOUNTAINS
AND VALLEYS. THE WINTER STORM WATCH REMAINS ACROSS THE AREA.
ADDITIONAL LOCATIONS LOOK FAVORABLE FOR THE NEED OF WINTER WEATHER
ADVISORIES...AND SNOWFALL TOTALS SHOULD BE ABLE TO BE FINALIZED
DURING THE UPCOMING SHIFT. SIMULTANEOUSLY...MODELS CONTINUE TO
INDICATE THE POTENTIAL FOR VERY STRONG WINDS ACROSS SWEETWATER
COUNTY AND INTO THE GREEN MOUNTAINS AND RATTLESNAKE RANGE SUNDAY
AFTERNOON AND EVENING. ANOTHER HIGH WIND WATCH HAS BEEN ISSUED TO
ACCOUNT FOR THESE POTENTIALLY STRONG WINDS.

SNOWFALL AND WIND IS EXPECTED TO WEAKEN MONDAY AS NORTHWEST FLOW
WORKS TO BUILD OVER THE AREA...WITH MOST ACTIVITY WANED BY MONDAY
AFTERNOON. SOME LIGHT SNOWFALL WILL REMAIN POSSIBLE ACROSS AREAS
EAST OF THE DIVIDE LATE MONDAY AS THE SYSTEM CONTINUES TO MOVE
INTO THE CENTRAL PLAINS.

.LONG TERM...TUESDAY THROUGH SATURDAY

QUITE THE MODEL DIVERGENCE TONIGHT BETWEEN THE GFS AND THE ECMWF.
THE MODELS START OUT PRETTY CLOSE THROUGH TUESDAY WITH TRANSITORY
RIDGE MOVING ACROSS THE AREA AFTER OUR SUN/MON SNOW AND WIND EVENT.
ECMWF HAS SOME MOISTURE AND UPGLIDE IN THE PATTERN ALREADY TUESDAY
SO SOME CHANCE POPS REMAIN...ESPECIALLY BY TUESDAY NIGHT. AFTER
THAT...THE CHANGES BECOME VERY SIGNIFICANT. THE 00Z GFS ALLOWS THE
CHRISTMAS EVE/CHRISTMAS DAY SYSTEM TO COME IN AT A HIGHER LATITUDE
WITH LESS RIDGING BEHIND IT. THIS SOLUTION HAS A SEWD MOVING
DISTURBANCE COMING THROUGH WITH THE MAIN EFFECT BEING STRONG TO HIGH
WIND ACROSS THE LOWER ELEVATIONS AND A QUICK SHOT OF SNOW...MAINLY
IN THE MOUNTAINS. THE ECMWF ON THE OTHER HAND IS STILL SHOWING THIS
SYSTEM DROPPING INTO THE PACNW AND THEN THE NRN GREAT BASIN AS
RIDGING DEVELOPS QUICKLY BEHIND IT. THE SYSTEM THEN CLOSES OFF OVER
SRN WYOMING ON CHRISTMAS DAY WITH WIDESPREAD SNOW SPREADING EWD AND
SWD CHRISTMAS EVE INTO EARLY CHRISTMAS DAY. THE DEVELOPMENT OF THIS
SYSTEM IS STILL A COMBINATION OF THE CURRENT TROUGH OVER THE
CENTRAL PACIFIC ACCOMPANIED BY AT LEAST A 170-180KT JET AND A
POCKET OF COLD AIR POURING SOUTH IN THE KAMCHATKA REGION. A STRONG
TROUGH WITH VERY COLD AIR BEHIND THIS SYSTEM AND A LEAD
DISTURBANCE ARE RESPONSIBLE FOR THE UPSTREAM RIDGE ALONG THE COAST
THAT THE ECMWF ESPECIALLY SHOWS. THE GFS HAS A SIMILAR SCENARIO
BUT DIVERGES SLIGHTLY NOT ALLOWING THE RIDGE TO BUILD UPSTREAM AS
MUCH. THAT MAKES ALL THE DIFFERENCE IN THE WORLD FOR OUR SENSIBLE
WEATHER. STICKING CLOSER TO THE MORE CONSISTENT ECMWF AND USUALLY
BETTER EURO IN THIS SCENARIO WHICH MEANS LITTLE CHANGE FOR OUR
GOING FORECAST. COLD BEHIND THIS SYSTEM...ESPECIALLY WITH THE
ECMWF SOLUTION FRIDAY NIGHT. ANOTHER POTENTIAL SEWD COLD MOVING
SHORTWAVE MAY MOVE INTO THE NWRN PARTS AT THE END OF THIS PERIOD.
THIS SYSTEM IS ACTUALLY THE ONE EXPECTED TO PUMP SOME WARM AIR
INTO OUR RIDGE ALONG THE COAST AND AID IN THE DIGGING OUR
CHRISTMAS SYSTEM.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 18Z SUNDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS.  STRONG WEST WINDS WILL PRODUCE
AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST SLOPES OF
THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR ALONG AND NEAR THE SLOPES OF THE MOUNTAINS.

.FIRE WEATHER...

A PLETHORA OF POTENTIALLY ADVERSE WEATHER CONDITIONS ARE POSSIBLE
OVER THE NEXT COUPLE DAYS. STRONG WIND MAY DEVELOP ACROSS THE CODY
FOOTHILLS LATE THIS EVENING...AND CONTINUE INTO SUNDAY MORNING.
MEANWHILE...SNOWFALL WILL INTENSIFY ACROSS THE WESTERN MOUNTAINS
AND VALLEYS...AND WILL PERSIST THROUGH MONDAY MORNING. SNOWFALL
MAY COMBINE WITH GUSTY WIND AT TIMES. AS THE SYSTEM CONTINUES TO
IMPACT THE STATE...STRONG WIND IS POSSIBLE TO DEVELOP ACROSS GREEN
MOUNTAIN AND RATTLESNAKE RANGE...ALONG WITH THE INTERSTATE 80
CORRIDOR THROUGH SWEETWATER COUNTY. THESE STRONG WINDS AND
COMBINED SNOW AND WIND WILL MAKE FOR GENERALLY UNFAVORABLE BURN
CONDITIONS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING
WYZ019-028>030.

WINTER STORM WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ002-014-015-025.

WINTER STORM WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
MORNING WYZ001-012-013-023-024.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH SUNDAY
MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...SKRBAC
AVIATION...C.BAKER
FIRE WEATHER...BRANHAM







000
FXUS65 KRIW 201728
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1028 AM MST SAT DEC 20 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

AN INTERESTING FORECAST PERIOD WITH A LOT OF POTENTIALLY
SIGNIFICANT WEATHER DEVELOPING. A NEARLY ZONAL FLOW PATTERN IS
EXPECTED THIS MORNING AND AFTERNOON...WITH SOME MOISTURE INCREASE
SNOWFALL COVERAGE A BIT ACROSS WESTERN WYOMING.

A PACIFIC STORM SYSTEM WILL CONTINUE TO MOVE THROUGH THE
INTERMOUNTAIN WEST SATURDAY EVENING...WITH SNOWFALL INCREASING
ACROSS WESTERN WYOMING. ADDITIONALLY...AN INCREASED TEMPERATURE
GRADIENT IS EXPECTED BETWEEN CODY AND THE EASTERN PORTION OF
YELLOWSTONE NATIONAL PARK. ADDITIONAL MOUNTAIN WAVE SIGNATURES ARE
BEING DEMONSTRATED IN CURRENT MODEL ANALYSIS...WITH VERY STRONG
WIND POSSIBLE AROUND THE FAVORED CLARK AREA. A HIGH WIND WATCH IS
IN EFFECT FOR THIS LOCATION.

SNOWFALL IS EXPECTED TO INCREASE TONIGHT AND PERSIST THROUGH
MONDAY MORNING. SNOWFALL IS LOOKING TO BECOME HEAVY AT TIMES WITH
SIGNIFICANT ACCUMULATIONS POSSIBLE ACROSS THE WESTERN MOUNTAINS
AND VALLEYS. THE WINTER STORM WATCH REMAINS ACROSS THE AREA.
ADDITIONAL LOCATIONS LOOK FAVORABLE FOR THE NEED OF WINTER WEATHER
ADVISORIES...AND SNOWFALL TOTALS SHOULD BE ABLE TO BE FINALIZED
DURING THE UPCOMING SHIFT. SIMULTANEOUSLY...MODELS CONTINUE TO
INDICATE THE POTENTIAL FOR VERY STRONG WINDS ACROSS SWEETWATER
COUNTY AND INTO THE GREEN MOUNTAINS AND RATTLESNAKE RANGE SUNDAY
AFTERNOON AND EVENING. ANOTHER HIGH WIND WATCH HAS BEEN ISSUED TO
ACCOUNT FOR THESE POTENTIALLY STRONG WINDS.

SNOWFALL AND WIND IS EXPECTED TO WEAKEN MONDAY AS NORTHWEST FLOW
WORKS TO BUILD OVER THE AREA...WITH MOST ACTIVITY WANED BY MONDAY
AFTERNOON. SOME LIGHT SNOWFALL WILL REMAIN POSSIBLE ACROSS AREAS
EAST OF THE DIVIDE LATE MONDAY AS THE SYSTEM CONTINUES TO MOVE
INTO THE CENTRAL PLAINS.

.LONG TERM...TUESDAY THROUGH SATURDAY

QUITE THE MODEL DIVERGENCE TONIGHT BETWEEN THE GFS AND THE ECMWF.
THE MODELS START OUT PRETTY CLOSE THROUGH TUESDAY WITH TRANSITORY
RIDGE MOVING ACROSS THE AREA AFTER OUR SUN/MON SNOW AND WIND EVENT.
ECMWF HAS SOME MOISTURE AND UPGLIDE IN THE PATTERN ALREADY TUESDAY
SO SOME CHANCE POPS REMAIN...ESPECIALLY BY TUESDAY NIGHT. AFTER
THAT...THE CHANGES BECOME VERY SIGNIFICANT. THE 00Z GFS ALLOWS THE
CHRISTMAS EVE/CHRISTMAS DAY SYSTEM TO COME IN AT A HIGHER LATITUDE
WITH LESS RIDGING BEHIND IT. THIS SOLUTION HAS A SEWD MOVING
DISTURBANCE COMING THROUGH WITH THE MAIN EFFECT BEING STRONG TO HIGH
WIND ACROSS THE LOWER ELEVATIONS AND A QUICK SHOT OF SNOW...MAINLY
IN THE MOUNTAINS. THE ECMWF ON THE OTHER HAND IS STILL SHOWING THIS
SYSTEM DROPPING INTO THE PACNW AND THEN THE NRN GREAT BASIN AS
RIDGING DEVELOPS QUICKLY BEHIND IT. THE SYSTEM THEN CLOSES OFF OVER
SRN WYOMING ON CHRISTMAS DAY WITH WIDESPREAD SNOW SPREADING EWD AND
SWD CHRISTMAS EVE INTO EARLY CHRISTMAS DAY. THE DEVELOPMENT OF THIS
SYSTEM IS STILL A COMBINATION OF THE CURRENT TROUGH OVER THE
CENTRAL PACIFIC ACCOMPANIED BY AT LEAST A 170-180KT JET AND A
POCKET OF COLD AIR POURING SOUTH IN THE KAMCHATKA REGION. A STRONG
TROUGH WITH VERY COLD AIR BEHIND THIS SYSTEM AND A LEAD
DISTURBANCE ARE RESPONSIBLE FOR THE UPSTREAM RIDGE ALONG THE COAST
THAT THE ECMWF ESPECIALLY SHOWS. THE GFS HAS A SIMILAR SCENARIO
BUT DIVERGES SLIGHTLY NOT ALLOWING THE RIDGE TO BUILD UPSTREAM AS
MUCH. THAT MAKES ALL THE DIFFERENCE IN THE WORLD FOR OUR SENSIBLE
WEATHER. STICKING CLOSER TO THE MORE CONSISTENT ECMWF AND USUALLY
BETTER EURO IN THIS SCENARIO WHICH MEANS LITTLE CHANGE FOR OUR
GOING FORECAST. COLD BEHIND THIS SYSTEM...ESPECIALLY WITH THE
ECMWF SOLUTION FRIDAY NIGHT. ANOTHER POTENTIAL SEWD COLD MOVING
SHORTWAVE MAY MOVE INTO THE NWRN PARTS AT THE END OF THIS PERIOD.
THIS SYSTEM IS ACTUALLY THE ONE EXPECTED TO PUMP SOME WARM AIR
INTO OUR RIDGE ALONG THE COAST AND AID IN THE DIGGING OUR
CHRISTMAS SYSTEM.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 18Z SUNDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS.  STRONG WEST WINDS WILL PRODUCE
AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST SLOPES OF
THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR ALONG AND NEAR THE SLOPES OF THE MOUNTAINS.

.FIRE WEATHER...

A PLETHORA OF POTENTIALLY ADVERSE WEATHER CONDITIONS ARE POSSIBLE
OVER THE NEXT COUPLE DAYS. STRONG WIND MAY DEVELOP ACROSS THE CODY
FOOTHILLS LATE THIS EVENING...AND CONTINUE INTO SUNDAY MORNING.
MEANWHILE...SNOWFALL WILL INTENSIFY ACROSS THE WESTERN MOUNTAINS
AND VALLEYS...AND WILL PERSIST THROUGH MONDAY MORNING. SNOWFALL
MAY COMBINE WITH GUSTY WIND AT TIMES. AS THE SYSTEM CONTINUES TO
IMPACT THE STATE...STRONG WIND IS POSSIBLE TO DEVELOP ACROSS GREEN
MOUNTAIN AND RATTLESNAKE RANGE...ALONG WITH THE INTERSTATE 80
CORRIDOR THROUGH SWEETWATER COUNTY. THESE STRONG WINDS AND
COMBINED SNOW AND WIND WILL MAKE FOR GENERALLY UNFAVORABLE BURN
CONDITIONS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING
WYZ019-028>030.

WINTER STORM WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ002-014-015-025.

WINTER STORM WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
MORNING WYZ001-012-013-023-024.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH SUNDAY
MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...SKRBAC
AVIATION...C.BAKER
FIRE WEATHER...BRANHAM








000
FXUS65 KRIW 201013
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
313 AM MST SAT DEC 20 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

AN INTERESTING FORECAST PERIOD WITH A LOT OF POTENTIALLY
SIGNIFICANT WEATHER DEVELOPING. A NEARLY ZONAL FLOW PATTERN IS
EXPECTED THIS MORNING AND AFTERNOON...WITH SOME MOISTURE INCREASE
SNOWFALL COVERAGE A BIT ACROSS WESTERN WYOMING.

A PACIFIC STORM SYSTEM WILL CONTINUE TO MOVE THROUGH THE
INTERMOUNTAIN WEST SATURDAY EVENING...WITH SNOWFALL INCREASING
ACROSS WESTERN WYOMING. ADDITIONALLY...AN INCREASED TEMPERATURE
GRADIENT IS EXPECTED BETWEEN CODY AND THE EASTERN PORTION OF
YELLOWSTONE NATIONAL PARK. ADDITIONAL MOUNTAIN WAVE SIGNATURES ARE
BEING DEMONSTRATED IN CURRENT MODEL ANALYSIS...WITH VERY STRONG
WIND POSSIBLE AROUND THE FAVORED CLARK AREA. A HIGH WIND WATCH IS
IN EFFECT FOR THIS LOCATION.

SNOWFALL IS EXPECTED TO INCREASE TONIGHT AND PERSIST THROUGH
MONDAY MORNING. SNOWFALL IS LOOKING TO BECOME HEAVY AT TIMES WITH
SIGNIFICANT ACCUMULATIONS POSSIBLE ACROSS THE WESTERN MOUNTAINS
AND VALLEYS. THE WINTER STORM WATCH REMAINS ACROSS THE AREA.
ADDITIONAL LOCATIONS LOOK FAVORABLE FOR THE NEED OF WINTER WEATHER
ADVISORIES...AND SNOWFALL TOTALS SHOULD BE ABLE TO BE FINALIZED
DURING THE UPCOMING SHIFT. SIMULTANEOUSLY...MODELS CONTINUE TO
INDICATE THE POTENTIAL FOR VERY STRONG WINDS ACROSS SWEETWATER
COUNTY AND INTO THE GREEN MOUNTAINS AND RATTLESNAKE RANGE SUNDAY
AFTERNOON AND EVENING. ANOTHER HIGH WIND WATCH HAS BEEN ISSUED TO
ACCOUNT FOR THESE POTENTIALLY STRONG WINDS.

SNOWFALL AND WIND IS EXPECTED TO WEAKEN MONDAY AS NORTHWEST FLOW
WORKS TO BUILD OVER THE AREA...WITH MOST ACTIVITY WANED BY MONDAY
AFTERNOON. SOME LIGHT SNOWFALL WILL REMAIN POSSIBLE ACROSS AREAS
EAST OF THE DIVIDE LATE MONDAY AS THE SYSTEM CONTINUES TO MOVE
INTO THE CENTRAL PLAINS.

.LONG TERM...TUESDAY THROUGH SATURDAY

QUITE THE MODEL DIVERGENCE TONIGHT BETWEEN THE GFS AND THE ECMWF.
THE MODELS START OUT PRETTY CLOSE THROUGH TUESDAY WITH TRANSITORY
RIDGE MOVING ACROSS THE AREA AFTER OUR SUN/MON SNOW AND WIND EVENT.
ECMWF HAS SOME MOISTURE AND UPGLIDE IN THE PATTERN ALREADY TUESDAY
SO SOME CHANCE POPS REMAIN...ESPECIALLY BY TUESDAY NIGHT. AFTER
THAT...THE CHANGES BECOME VERY SIGNIFICANT. THE 00Z GFS ALLOWS THE
CHRISTMAS EVE/CHRISTMAS DAY SYSTEM TO COME IN AT A HIGHER LATITUDE
WITH LESS RIDGING BEHIND IT. THIS SOLUTION HAS A SEWD MOVING
DISTURBANCE COMING THROUGH WITH THE MAIN EFFECT BEING STRONG TO HIGH
WIND ACROSS THE LOWER ELEVATIONS AND A QUICK SHOT OF SNOW...MAINLY
IN THE MOUNTAINS. THE ECMWF ON THE OTHER HAND IS STILL SHOWING THIS
SYSTEM DROPPING INTO THE PACNW AND THEN THE NRN GREAT BASIN AS
RIDGING DEVELOPS QUICKLY BEHIND IT. THE SYSTEM THEN CLOSES OFF OVER
SRN WYOMING ON CHRISTMAS DAY WITH WIDESPREAD SNOW SPREADING EWD AND
SWD CHRISTMAS EVE INTO EARLY CHRISTMAS DAY. THE DEVELOPMENT OF THIS
SYSTEM IS STILL A COMBINATION OF THE CURRENT TROUGH OVER THE
CENTRAL PACIFIC ACCOMPANIED BY AT LEAST A 170-180KT JET AND A
POCKET OF COLD AIR POURING SOUTH IN THE KAMCHATKA REGION. A STRONG
TROUGH WITH VERY COLD AIR BEHIND THIS SYSTEM AND A LEAD
DISTURBANCE ARE RESPONSIBLE FOR THE UPSTREAM RIDGE ALONG THE COAST
THAT THE ECMWF ESPECIALLY SHOWS. THE GFS HAS A SIMILAR SCENARIO
BUT DIVERGES SLIGHTLY NOT ALLOWING THE RIDGE TO BUILD UPSTREAM AS
MUCH. THAT MAKES ALL THE DIFFERENCE IN THE WORLD FOR OUR SENSIBLE
WEATHER. STICKING CLOSER TO THE MORE CONSISTENT ECMWF AND USUALLY
BETTER EURO IN THIS SCENARIO WHICH MEANS LITTLE CHANGE FOR OUR
GOING FORECAST. COLD BEHIND THIS SYSTEM...ESPECIALLY WITH THE
ECMWF SOLUTION FRIDAY NIGHT. ANOTHER POTENTIAL SEWD COLD MOVING
SHORTWAVE MAY MOVE INTO THE NWRN PARTS AT THE END OF THIS PERIOD.
THIS SYSTEM IS ACTUALLY THE ONE EXPECTED TO PUMP SOME WARM AIR
INTO OUR RIDGE ALONG THE COAST AND AID IN THE DIGGING OUR
CHRISTMAS SYSTEM.

&&

.AVIATION.../12Z ISSUANCE/

INCREASING MOISTURE PER MODELS INTO WESTERN WYOMING ON SATURDAY.
SNOW WILL INCREASE AND BECOME MODERATE TO HEAVY BY SATURDAY
NIGHT...ESPECIALLY IN THE MOUNTAINS AND POSSIBLY NEAR KJAC. THIS
WILL RESULT IN MOUNTAIN OBSCURATION FOR ALL MOUNTAIN RANGES.

OUTSIDE OF THE WIND RIVER BASIN OF CENTRAL WYOMING...VFR CONDITIONS
CAN BE EXPECTED THROUGH SATURDAY EAST OF THE DIVIDE. WITH A
TIGHTENING PRESSURE GRADIENT WINDS WILL INCREASE
SATURDAY...ESPECIALLY ACROSS THE SOUTHWESTERN WIND CORRIDOR FROM
KRKS TO KCPR. ANY FOG AT KLND AND KRIW SHOULD BEGIN TO LEFT AROUND
15 TO 16Z AND BE FULLY LIFTED BY 19Z.

&&

.FIRE WEATHER...

A PLETHORA OF POTENTIALLY ADVERSE WEATHER CONDITIONS ARE POSSIBLE
OVER THE NEXT COUPLE DAYS. STRONG WIND MAY DEVELOP ACROSS THE CODY
FOOTHILLS LATE THIS EVENING...AND CONTINUE INTO SUNDAY MORNING.
MEANWHILE...SNOWFALL WILL INTENSIFY ACROSS THE WESTERN MOUNTAINS
AND VALLEYS...AND WILL PERSIST THROUGH MONDAY MORNING. SNOWFALL
MAY COMBINE WITH GUSTY WIND AT TIMES. AS THE SYSTEM CONTINUES TO
IMPACT THE STATE...STRONG WIND IS POSSIBLE TO DEVELOP ACROSS GREEN
MOUNTAIN AND RATTLESNAKE RANGE...ALONG WITH THE INTERSTATE 80
CORRIDOR THROUGH SWEETWATER COUNTY. THESE STRONG WINDS AND
COMBINED SNOW AND WIND WILL MAKE FOR GENERALLY UNFAVORABLE BURN
CONDITIONS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING
WYZ019-028>030.

WINTER STORM WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ002-014-015-025.

WINTER STORM WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM THIS EVENING THROUGH SUNDAY MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...SKRBAC
AVIATION...HATTINGS
FIRE WEATHER...BRANHAM









000
FXUS65 KRIW 201013
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
313 AM MST SAT DEC 20 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

AN INTERESTING FORECAST PERIOD WITH A LOT OF POTENTIALLY
SIGNIFICANT WEATHER DEVELOPING. A NEARLY ZONAL FLOW PATTERN IS
EXPECTED THIS MORNING AND AFTERNOON...WITH SOME MOISTURE INCREASE
SNOWFALL COVERAGE A BIT ACROSS WESTERN WYOMING.

A PACIFIC STORM SYSTEM WILL CONTINUE TO MOVE THROUGH THE
INTERMOUNTAIN WEST SATURDAY EVENING...WITH SNOWFALL INCREASING
ACROSS WESTERN WYOMING. ADDITIONALLY...AN INCREASED TEMPERATURE
GRADIENT IS EXPECTED BETWEEN CODY AND THE EASTERN PORTION OF
YELLOWSTONE NATIONAL PARK. ADDITIONAL MOUNTAIN WAVE SIGNATURES ARE
BEING DEMONSTRATED IN CURRENT MODEL ANALYSIS...WITH VERY STRONG
WIND POSSIBLE AROUND THE FAVORED CLARK AREA. A HIGH WIND WATCH IS
IN EFFECT FOR THIS LOCATION.

SNOWFALL IS EXPECTED TO INCREASE TONIGHT AND PERSIST THROUGH
MONDAY MORNING. SNOWFALL IS LOOKING TO BECOME HEAVY AT TIMES WITH
SIGNIFICANT ACCUMULATIONS POSSIBLE ACROSS THE WESTERN MOUNTAINS
AND VALLEYS. THE WINTER STORM WATCH REMAINS ACROSS THE AREA.
ADDITIONAL LOCATIONS LOOK FAVORABLE FOR THE NEED OF WINTER WEATHER
ADVISORIES...AND SNOWFALL TOTALS SHOULD BE ABLE TO BE FINALIZED
DURING THE UPCOMING SHIFT. SIMULTANEOUSLY...MODELS CONTINUE TO
INDICATE THE POTENTIAL FOR VERY STRONG WINDS ACROSS SWEETWATER
COUNTY AND INTO THE GREEN MOUNTAINS AND RATTLESNAKE RANGE SUNDAY
AFTERNOON AND EVENING. ANOTHER HIGH WIND WATCH HAS BEEN ISSUED TO
ACCOUNT FOR THESE POTENTIALLY STRONG WINDS.

SNOWFALL AND WIND IS EXPECTED TO WEAKEN MONDAY AS NORTHWEST FLOW
WORKS TO BUILD OVER THE AREA...WITH MOST ACTIVITY WANED BY MONDAY
AFTERNOON. SOME LIGHT SNOWFALL WILL REMAIN POSSIBLE ACROSS AREAS
EAST OF THE DIVIDE LATE MONDAY AS THE SYSTEM CONTINUES TO MOVE
INTO THE CENTRAL PLAINS.

.LONG TERM...TUESDAY THROUGH SATURDAY

QUITE THE MODEL DIVERGENCE TONIGHT BETWEEN THE GFS AND THE ECMWF.
THE MODELS START OUT PRETTY CLOSE THROUGH TUESDAY WITH TRANSITORY
RIDGE MOVING ACROSS THE AREA AFTER OUR SUN/MON SNOW AND WIND EVENT.
ECMWF HAS SOME MOISTURE AND UPGLIDE IN THE PATTERN ALREADY TUESDAY
SO SOME CHANCE POPS REMAIN...ESPECIALLY BY TUESDAY NIGHT. AFTER
THAT...THE CHANGES BECOME VERY SIGNIFICANT. THE 00Z GFS ALLOWS THE
CHRISTMAS EVE/CHRISTMAS DAY SYSTEM TO COME IN AT A HIGHER LATITUDE
WITH LESS RIDGING BEHIND IT. THIS SOLUTION HAS A SEWD MOVING
DISTURBANCE COMING THROUGH WITH THE MAIN EFFECT BEING STRONG TO HIGH
WIND ACROSS THE LOWER ELEVATIONS AND A QUICK SHOT OF SNOW...MAINLY
IN THE MOUNTAINS. THE ECMWF ON THE OTHER HAND IS STILL SHOWING THIS
SYSTEM DROPPING INTO THE PACNW AND THEN THE NRN GREAT BASIN AS
RIDGING DEVELOPS QUICKLY BEHIND IT. THE SYSTEM THEN CLOSES OFF OVER
SRN WYOMING ON CHRISTMAS DAY WITH WIDESPREAD SNOW SPREADING EWD AND
SWD CHRISTMAS EVE INTO EARLY CHRISTMAS DAY. THE DEVELOPMENT OF THIS
SYSTEM IS STILL A COMBINATION OF THE CURRENT TROUGH OVER THE
CENTRAL PACIFIC ACCOMPANIED BY AT LEAST A 170-180KT JET AND A
POCKET OF COLD AIR POURING SOUTH IN THE KAMCHATKA REGION. A STRONG
TROUGH WITH VERY COLD AIR BEHIND THIS SYSTEM AND A LEAD
DISTURBANCE ARE RESPONSIBLE FOR THE UPSTREAM RIDGE ALONG THE COAST
THAT THE ECMWF ESPECIALLY SHOWS. THE GFS HAS A SIMILAR SCENARIO
BUT DIVERGES SLIGHTLY NOT ALLOWING THE RIDGE TO BUILD UPSTREAM AS
MUCH. THAT MAKES ALL THE DIFFERENCE IN THE WORLD FOR OUR SENSIBLE
WEATHER. STICKING CLOSER TO THE MORE CONSISTENT ECMWF AND USUALLY
BETTER EURO IN THIS SCENARIO WHICH MEANS LITTLE CHANGE FOR OUR
GOING FORECAST. COLD BEHIND THIS SYSTEM...ESPECIALLY WITH THE
ECMWF SOLUTION FRIDAY NIGHT. ANOTHER POTENTIAL SEWD COLD MOVING
SHORTWAVE MAY MOVE INTO THE NWRN PARTS AT THE END OF THIS PERIOD.
THIS SYSTEM IS ACTUALLY THE ONE EXPECTED TO PUMP SOME WARM AIR
INTO OUR RIDGE ALONG THE COAST AND AID IN THE DIGGING OUR
CHRISTMAS SYSTEM.

&&

.AVIATION.../12Z ISSUANCE/

INCREASING MOISTURE PER MODELS INTO WESTERN WYOMING ON SATURDAY.
SNOW WILL INCREASE AND BECOME MODERATE TO HEAVY BY SATURDAY
NIGHT...ESPECIALLY IN THE MOUNTAINS AND POSSIBLY NEAR KJAC. THIS
WILL RESULT IN MOUNTAIN OBSCURATION FOR ALL MOUNTAIN RANGES.

OUTSIDE OF THE WIND RIVER BASIN OF CENTRAL WYOMING...VFR CONDITIONS
CAN BE EXPECTED THROUGH SATURDAY EAST OF THE DIVIDE. WITH A
TIGHTENING PRESSURE GRADIENT WINDS WILL INCREASE
SATURDAY...ESPECIALLY ACROSS THE SOUTHWESTERN WIND CORRIDOR FROM
KRKS TO KCPR. ANY FOG AT KLND AND KRIW SHOULD BEGIN TO LEFT AROUND
15 TO 16Z AND BE FULLY LIFTED BY 19Z.

&&

.FIRE WEATHER...

A PLETHORA OF POTENTIALLY ADVERSE WEATHER CONDITIONS ARE POSSIBLE
OVER THE NEXT COUPLE DAYS. STRONG WIND MAY DEVELOP ACROSS THE CODY
FOOTHILLS LATE THIS EVENING...AND CONTINUE INTO SUNDAY MORNING.
MEANWHILE...SNOWFALL WILL INTENSIFY ACROSS THE WESTERN MOUNTAINS
AND VALLEYS...AND WILL PERSIST THROUGH MONDAY MORNING. SNOWFALL
MAY COMBINE WITH GUSTY WIND AT TIMES. AS THE SYSTEM CONTINUES TO
IMPACT THE STATE...STRONG WIND IS POSSIBLE TO DEVELOP ACROSS GREEN
MOUNTAIN AND RATTLESNAKE RANGE...ALONG WITH THE INTERSTATE 80
CORRIDOR THROUGH SWEETWATER COUNTY. THESE STRONG WINDS AND
COMBINED SNOW AND WIND WILL MAKE FOR GENERALLY UNFAVORABLE BURN
CONDITIONS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING
WYZ019-028>030.

WINTER STORM WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ002-014-015-025.

WINTER STORM WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM THIS EVENING THROUGH SUNDAY MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...SKRBAC
AVIATION...HATTINGS
FIRE WEATHER...BRANHAM










000
FXUS65 KRIW 200645
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1145 PM MST FRI DEC 19 2014

.SHORT TERM...TONIGHT THROUGH SATURDAY
UPDATED TO REMOVE THE DENSE FOG ADVISORY FOR THE LANDER FOOTHILLS
AND WIND RIVER BASIN. CONSIDERABLE MID AND HIGH CLOUDS HAS
INTERRUPTED THE DIURNAL CYCLE AND DIMINISHED THE CHANCE OF
WIDESPREAD DENSE FOG.

IMPRESSIVE WEEK FOR FOG ACROSS PARTS OF THE WIND RIVER BASIN OF
WEST CENTRAL WYOMING. THE ENVIRONMENT IS STILL CONDUCIVE FOR
FREEZING FOG TO CONTINUE ONE MORE NIGHT...ESPECIALLY NEAR
RIVERTON. IT MAY NOT BE AS WIDESPREAD AS PAST FEW NIGHTS.
NONETHELESS...WILL REISSUE DENSE FOG ADVISORY UNTIL 8 AM MST
SATURDAY MORNING. THINKING IS THAT MORE WESTERLY FLOW ABOVE THE
SURFACE AND WEAK SHORTWAVE ALOFT WILL HELP ERODE ALL FOG/LOW
STRATUS BY MID MORNING SATURDAY. EXPECT UNLIMITED VISIBILITY BY
SATURDAY AFTERNOON.

OTHERWISE...SHORTWAVE RIDGING THIS EVENING GIVES WAY TO WESTERLY
FLOW ALOFT. THIS FLOW ALOFT WILL INCREASE DURING THE DAY SATURDAY.
ISENTROPIC LIFT OVER FAR WESTERN MOUNTAINS THROUGH MUCH OF THE DAY
SATURDAY WILL RESULT IN AREAS OF LIGHT TO MODERATE SNOW.
THIS WILL BE THE APPETIZER TO WHAT IS ABOUT TO OCCUR WEST OF THE
DIVIDE FOR THE REMAINDER OF WEEKEND. THESE WINTRY DETAILS ARE
INTRODUCED IN THE LONG TERM DISCUSSION.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

THE BEGINNING OF THE LONG TERM MARKS THE ONSLAUGHT OF MOISTURE TO
WESTERN WYOMING FOR THE NEXT 36 HOURS.  AS NOTED BY THE PREVIOUS
SHIFT...A WINTER STORM WATCH IS CURRENTLY IN EFFECT FOR FAR WESTERN
WYOMING STARTING 800PM SATURDAY NIGHT...AND THEN INCLUDES THE
ABSAROKAS...WIND RIVERS...AND GREEN RIVER FOOTHILLS ZONES AT 1100PM.
THE WEST TO SOUTHWEST SATURATED FLOW WILL FIRST IMPACT THE WEST SIDE
OF THE TETONS AND SW PORTION OF YNP.  AFTER MIDNIGHT...THE INTENSITY
SHOULD INCREASE IN THE WESTERN MOUNTAINS AS THE LAPSE RATES INCREASE
ALONG WITH THE MID LEVEL FLOW AROUND 40 KNOTS.  THE MODELS ARE ALL
IN QUITE GOOD AGREEMENT WITH THE OVERALL STORM MOVEMENT AND
PRECIPITATION EXPECTATIONS.  FOR THE WESTERN MOUNTAINS...THE
OROGRAPHIC SNOW MODEL ESTIMATES 18-30 INCHES POTENTIAL SNOW ON THE
WESTERN SLOPES OF THE TETONS UNDER PRIME CONDITIONS.  THE
NEIGHBORING VALLEYS ARE LIKELY TO SEE 8-10 INCHES WITH 12-14 IN
LOCALLY FAVORABLE LOCATIONS LIKE MOOSE AND SMOOT. AS THE FLOW
BECOMES MORE WEST NORTHWEST LATER ON SUNDAY...THE MODELS ARE
INDICATING BETTER OROGRAPHICS ALONG THE SALT AND WYOMING RANGES AS
WELL AS INTO THE BONDURANT AND CORA AREAS.

THE GFS HOWEVER INDICATES MORE POTENTIAL FORCING WITH A STRONGER
SHORTWAVE TROUGH MOVING THROUGH MONTANA INTO THE NORTHERN PLAINS ON
SUNDAY.  THE RESULTING MID LEVEL BAROCLINIC BOUNDARY FROM SOUTHERN
MT INTO NE WY ALLOWS FOR ENHANCED PRECIPITATION IN THE NORTHERN BIG
HORN BASIN AND BIGHORN MOUNTAINS INTO JOHNSON COUNTY.  IF THIS
SITUATION PANS OUT WITH THE NORTHWEST FLOW...SOME MORE INTERESTING
HIGH SNOW AMOUNTS COULD OCCUR IN THE NORTHERN BIGHORNS AND ALONG THE
NORTH AND EAST SIDES OF THE BIG HORN BASIN.

THE ACCOMPANYING 120+ KNOT JET WITH THIS STORM SYSTEM WILL MAKE FOR
VERY INTERESTING CONDITIONS AT THE MID AND HIGHER ELEVATIONS.
MOUNTAIN TOP AND SLOPE WINDS ACROSS WESTERN WYOMING ARE LIKELY TO BE
WINDY THROUGHOUT THE PERIOD.  HAVE EVALUATED THE POTENTIAL FOR
STRONG WINDS IN THE CODY FOOTHILLS FROM SAT NIGHT INTO SUN MORN.
CROSS SECTIONS OF SEVERAL MODELS INDICATE AT THIS TIME THAT STRONGER
WINDS OF 50 KNOTS SHOULD STAY IN THE HIGHER ELEVATIONS OF THE
EASTERN ABSAROKAS WITH AROUND 30-40 KNOTS IN THE FOOTHILL
LOCATIONS.  AGREE WITH THE PREVIOUS SHIFT THAT WEST TO NORTHWEST
WIND WILL STRENGTHEN ON SUNDAY FROM DUBOIS INTO THE WIND RIVER
BASIN...AS WELL AS ACROSS SWEETWATER COUNTY INTO CENTRAL WYOMING.

BOTH THE GFS AND ECMWF MOVE THE SYSTEM INTO THE PLAINS BY MONDAY
NIGHT WITH RESIDUAL SHOWERS OVER EASTERN WYOMING MONDAY NIGHT.
WHILE BOTH MODELS DEVELOP THE RIDGE ACROSS THE WESTERN US ON
TUESDAY...THE GFS SOLUTION IS SHARPER...AND THE FLATTER ECMWF ALLOWS
OVER-THE-TOP MOISTURE AND WEAK ENERGY TO SLIDE INTO NW WY TUESDAY
NIGHT.  NOT CONFIDENT IN EITHER SOLUTION TO HAVE INDICATED SLIGHT
CHANCE OF SNOW IN THE FORECAST.  BOTH MODELS THEN BRING ANOTHER
PACIFIC TROUGH INTO OUR AREA LATE WEDNESDAY NIGHT INTO CHRISTMAS
DAY. THE ECMWF STILL DIGS THE SYSTEM FURTHER SOUTH THAN THE
GFS...YET IS SLIGHTLY FURTHER NORTH THAN 24 HOURS AGO.  THE GFS IS
KEEPING WITH A MORE OPEN PROGRESSIVE TROUGH THROUGH THE NORTHERN
ROCKIES.  AND THE PARALLEL GFS IS EVEN MORE PROGRESSIVE.  EITHER
WAY...A STORM WILL IMPACT WYOMING ON CHRISTMAS...BUT THERE IS MUCH
UNCERTAINTY AS TO THE PRECIPITATION...TEMPERATURE..AND WIND IMPACTS
AT THIS TIME DUE TO THE LOCATION AND TIMING DIFFERENCES.
REGARDLESS...FRIDAY LOOKS TO BE COLDER THAN EARLIER IN THE WEEK.

.AVIATION.../06Z ISSUANCE/

INCREASING MOISTURE PER MODELS INTO WESTERN WYOMING THIS WEEKEND.
SNOW WILL INCREASE AND BECOME MODERATE TO HEAVY BY LATE SATURDAY.
THIS WILL RESULT IN MOUNTAIN OBSCURATION FOR ALL MOUNTAIN RANGES.
IN ADDITION...WESTERN VALLEYS WILL BECOME IFR SATURDAY NIGHT AND
REMAIN THAT WAY THROUGH SUNDAY WITH LOW STRATUS AND SNOW.

OUTSIDE OF THE WIND RIVER BASIN OF CENTRAL WYOMING...VFR CONDITIONS
CAN BE EXPECTED THIS WEEKEND EAST OF THE DIVIDE. WITH A TIGHTENING
PRESSURE GRADIENT WINDS WILL INCREASE SATURDAY...ESPECIALLY ACROSS
THE SOUTHWESTERN WIND CORRIDOR FROM KRKS TO KCPR.

FOG HAS YET TO FORM AS OF 5Z AT KLND AND KRIW. LOCAL MODELS STILL
INDICATE FOG TO FORM AFTER MIDNIGHT AND LAST INTO THE EARLY MORNING
ALTHOUGH NOT AS WIDESPREAD AS PREVIOUS NIGHTS. WILL HAVE TO BE
MONITORED HOWEVER.

.FIRE WEATHER...

NO FIRE WEATHER CONCERNS OR ACTIVITIES SHOULD BE CONSIDERED THIS
WEEKEND. A POTENT WINTER STORM WILL MOVE INTO WESTERN WYOMING...
BRINGING MODERATE TO HEAVY SNOW BY SATURDAY NIGHT. IN FACT...A WINTER
STORM WATCH REMAINS IN EFFECT AND DETAILS ON THIS WATCH CAN BE
SEEN IN OUR WINTER WEATHER PRODUCT. WESTERLY SURFACE WIND WILL
ALSO INCREASE MOST LOCATIONS BY SATURDAY AFTERNOON. UNSETTLED
WEATHER WITH SNOW AND VERY GUSTY WIND WILL CONTINUE ACROSS WEST
CENTRAL WYOMING ON SUNDAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ002-014-015-025.

WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ001-012-013-023-024.

&&

$$

UPDATE...PS
SHORT TERM...KPL
LONG TERM...MCDONALD
AVIATION...HATTINGS
FIRE WEATHER...KPL








000
FXUS65 KRIW 200645
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1145 PM MST FRI DEC 19 2014

.SHORT TERM...TONIGHT THROUGH SATURDAY
UPDATED TO REMOVE THE DENSE FOG ADVISORY FOR THE LANDER FOOTHILLS
AND WIND RIVER BASIN. CONSIDERABLE MID AND HIGH CLOUDS HAS
INTERRUPTED THE DIURNAL CYCLE AND DIMINISHED THE CHANCE OF
WIDESPREAD DENSE FOG.

IMPRESSIVE WEEK FOR FOG ACROSS PARTS OF THE WIND RIVER BASIN OF
WEST CENTRAL WYOMING. THE ENVIRONMENT IS STILL CONDUCIVE FOR
FREEZING FOG TO CONTINUE ONE MORE NIGHT...ESPECIALLY NEAR
RIVERTON. IT MAY NOT BE AS WIDESPREAD AS PAST FEW NIGHTS.
NONETHELESS...WILL REISSUE DENSE FOG ADVISORY UNTIL 8 AM MST
SATURDAY MORNING. THINKING IS THAT MORE WESTERLY FLOW ABOVE THE
SURFACE AND WEAK SHORTWAVE ALOFT WILL HELP ERODE ALL FOG/LOW
STRATUS BY MID MORNING SATURDAY. EXPECT UNLIMITED VISIBILITY BY
SATURDAY AFTERNOON.

OTHERWISE...SHORTWAVE RIDGING THIS EVENING GIVES WAY TO WESTERLY
FLOW ALOFT. THIS FLOW ALOFT WILL INCREASE DURING THE DAY SATURDAY.
ISENTROPIC LIFT OVER FAR WESTERN MOUNTAINS THROUGH MUCH OF THE DAY
SATURDAY WILL RESULT IN AREAS OF LIGHT TO MODERATE SNOW.
THIS WILL BE THE APPETIZER TO WHAT IS ABOUT TO OCCUR WEST OF THE
DIVIDE FOR THE REMAINDER OF WEEKEND. THESE WINTRY DETAILS ARE
INTRODUCED IN THE LONG TERM DISCUSSION.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

THE BEGINNING OF THE LONG TERM MARKS THE ONSLAUGHT OF MOISTURE TO
WESTERN WYOMING FOR THE NEXT 36 HOURS.  AS NOTED BY THE PREVIOUS
SHIFT...A WINTER STORM WATCH IS CURRENTLY IN EFFECT FOR FAR WESTERN
WYOMING STARTING 800PM SATURDAY NIGHT...AND THEN INCLUDES THE
ABSAROKAS...WIND RIVERS...AND GREEN RIVER FOOTHILLS ZONES AT 1100PM.
THE WEST TO SOUTHWEST SATURATED FLOW WILL FIRST IMPACT THE WEST SIDE
OF THE TETONS AND SW PORTION OF YNP.  AFTER MIDNIGHT...THE INTENSITY
SHOULD INCREASE IN THE WESTERN MOUNTAINS AS THE LAPSE RATES INCREASE
ALONG WITH THE MID LEVEL FLOW AROUND 40 KNOTS.  THE MODELS ARE ALL
IN QUITE GOOD AGREEMENT WITH THE OVERALL STORM MOVEMENT AND
PRECIPITATION EXPECTATIONS.  FOR THE WESTERN MOUNTAINS...THE
OROGRAPHIC SNOW MODEL ESTIMATES 18-30 INCHES POTENTIAL SNOW ON THE
WESTERN SLOPES OF THE TETONS UNDER PRIME CONDITIONS.  THE
NEIGHBORING VALLEYS ARE LIKELY TO SEE 8-10 INCHES WITH 12-14 IN
LOCALLY FAVORABLE LOCATIONS LIKE MOOSE AND SMOOT. AS THE FLOW
BECOMES MORE WEST NORTHWEST LATER ON SUNDAY...THE MODELS ARE
INDICATING BETTER OROGRAPHICS ALONG THE SALT AND WYOMING RANGES AS
WELL AS INTO THE BONDURANT AND CORA AREAS.

THE GFS HOWEVER INDICATES MORE POTENTIAL FORCING WITH A STRONGER
SHORTWAVE TROUGH MOVING THROUGH MONTANA INTO THE NORTHERN PLAINS ON
SUNDAY.  THE RESULTING MID LEVEL BAROCLINIC BOUNDARY FROM SOUTHERN
MT INTO NE WY ALLOWS FOR ENHANCED PRECIPITATION IN THE NORTHERN BIG
HORN BASIN AND BIGHORN MOUNTAINS INTO JOHNSON COUNTY.  IF THIS
SITUATION PANS OUT WITH THE NORTHWEST FLOW...SOME MORE INTERESTING
HIGH SNOW AMOUNTS COULD OCCUR IN THE NORTHERN BIGHORNS AND ALONG THE
NORTH AND EAST SIDES OF THE BIG HORN BASIN.

THE ACCOMPANYING 120+ KNOT JET WITH THIS STORM SYSTEM WILL MAKE FOR
VERY INTERESTING CONDITIONS AT THE MID AND HIGHER ELEVATIONS.
MOUNTAIN TOP AND SLOPE WINDS ACROSS WESTERN WYOMING ARE LIKELY TO BE
WINDY THROUGHOUT THE PERIOD.  HAVE EVALUATED THE POTENTIAL FOR
STRONG WINDS IN THE CODY FOOTHILLS FROM SAT NIGHT INTO SUN MORN.
CROSS SECTIONS OF SEVERAL MODELS INDICATE AT THIS TIME THAT STRONGER
WINDS OF 50 KNOTS SHOULD STAY IN THE HIGHER ELEVATIONS OF THE
EASTERN ABSAROKAS WITH AROUND 30-40 KNOTS IN THE FOOTHILL
LOCATIONS.  AGREE WITH THE PREVIOUS SHIFT THAT WEST TO NORTHWEST
WIND WILL STRENGTHEN ON SUNDAY FROM DUBOIS INTO THE WIND RIVER
BASIN...AS WELL AS ACROSS SWEETWATER COUNTY INTO CENTRAL WYOMING.

BOTH THE GFS AND ECMWF MOVE THE SYSTEM INTO THE PLAINS BY MONDAY
NIGHT WITH RESIDUAL SHOWERS OVER EASTERN WYOMING MONDAY NIGHT.
WHILE BOTH MODELS DEVELOP THE RIDGE ACROSS THE WESTERN US ON
TUESDAY...THE GFS SOLUTION IS SHARPER...AND THE FLATTER ECMWF ALLOWS
OVER-THE-TOP MOISTURE AND WEAK ENERGY TO SLIDE INTO NW WY TUESDAY
NIGHT.  NOT CONFIDENT IN EITHER SOLUTION TO HAVE INDICATED SLIGHT
CHANCE OF SNOW IN THE FORECAST.  BOTH MODELS THEN BRING ANOTHER
PACIFIC TROUGH INTO OUR AREA LATE WEDNESDAY NIGHT INTO CHRISTMAS
DAY. THE ECMWF STILL DIGS THE SYSTEM FURTHER SOUTH THAN THE
GFS...YET IS SLIGHTLY FURTHER NORTH THAN 24 HOURS AGO.  THE GFS IS
KEEPING WITH A MORE OPEN PROGRESSIVE TROUGH THROUGH THE NORTHERN
ROCKIES.  AND THE PARALLEL GFS IS EVEN MORE PROGRESSIVE.  EITHER
WAY...A STORM WILL IMPACT WYOMING ON CHRISTMAS...BUT THERE IS MUCH
UNCERTAINTY AS TO THE PRECIPITATION...TEMPERATURE..AND WIND IMPACTS
AT THIS TIME DUE TO THE LOCATION AND TIMING DIFFERENCES.
REGARDLESS...FRIDAY LOOKS TO BE COLDER THAN EARLIER IN THE WEEK.

.AVIATION.../06Z ISSUANCE/

INCREASING MOISTURE PER MODELS INTO WESTERN WYOMING THIS WEEKEND.
SNOW WILL INCREASE AND BECOME MODERATE TO HEAVY BY LATE SATURDAY.
THIS WILL RESULT IN MOUNTAIN OBSCURATION FOR ALL MOUNTAIN RANGES.
IN ADDITION...WESTERN VALLEYS WILL BECOME IFR SATURDAY NIGHT AND
REMAIN THAT WAY THROUGH SUNDAY WITH LOW STRATUS AND SNOW.

OUTSIDE OF THE WIND RIVER BASIN OF CENTRAL WYOMING...VFR CONDITIONS
CAN BE EXPECTED THIS WEEKEND EAST OF THE DIVIDE. WITH A TIGHTENING
PRESSURE GRADIENT WINDS WILL INCREASE SATURDAY...ESPECIALLY ACROSS
THE SOUTHWESTERN WIND CORRIDOR FROM KRKS TO KCPR.

FOG HAS YET TO FORM AS OF 5Z AT KLND AND KRIW. LOCAL MODELS STILL
INDICATE FOG TO FORM AFTER MIDNIGHT AND LAST INTO THE EARLY MORNING
ALTHOUGH NOT AS WIDESPREAD AS PREVIOUS NIGHTS. WILL HAVE TO BE
MONITORED HOWEVER.

.FIRE WEATHER...

NO FIRE WEATHER CONCERNS OR ACTIVITIES SHOULD BE CONSIDERED THIS
WEEKEND. A POTENT WINTER STORM WILL MOVE INTO WESTERN WYOMING...
BRINGING MODERATE TO HEAVY SNOW BY SATURDAY NIGHT. IN FACT...A WINTER
STORM WATCH REMAINS IN EFFECT AND DETAILS ON THIS WATCH CAN BE
SEEN IN OUR WINTER WEATHER PRODUCT. WESTERLY SURFACE WIND WILL
ALSO INCREASE MOST LOCATIONS BY SATURDAY AFTERNOON. UNSETTLED
WEATHER WITH SNOW AND VERY GUSTY WIND WILL CONTINUE ACROSS WEST
CENTRAL WYOMING ON SUNDAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ002-014-015-025.

WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ001-012-013-023-024.

&&

$$

UPDATE...PS
SHORT TERM...KPL
LONG TERM...MCDONALD
AVIATION...HATTINGS
FIRE WEATHER...KPL







000
FXUS65 KRIW 200531
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1030 PM MST FRI DEC 19 2014


.SHORT TERM...TONIGHT THROUGH SATURDAY

IMPRESSIVE WEEK FOR FOG ACROSS PARTS OF THE WIND RIVER BASIN OF
WEST CENTRAL WYOMING. THE ENVIRONMENT IS STILL CONDUCIVE FOR
FREEZING FOG TO CONTINUE ONE MORE NIGHT...ESPECIALLY NEAR
RIVERTON. IT MAY NOT BE AS WIDESPREAD AS PAST FEW NIGHTS.
NONETHELESS...WILL REISSUE DENSE FOG ADVISORY UNTIL 8 AM MST
SATURDAY MORNING. THINKING IS THAT MORE WESTERLY FLOW ABOVE THE
SURFACE AND WEAK SHORTWAVE ALOFT WILL HELP ERODE ALL FOG/LOW
STRATUS BY MID MORNING SATURDAY. EXPECT UNLIMITED VISIBILITY BY
SATURDAY AFTERNOON.

OTHERWISE...SHORTWAVE RIDGING THIS EVENING GIVES WAY TO WESTERLY
FLOW ALOFT. THIS FLOW ALOFT WILL INCREASE DURING THE DAY SATURDAY.
ISENTROPIC LIFT OVER FAR WESTERN MOUNTAINS THROUGH MUCH OF THE DAY
SATURDAY WILL RESULT IN AREAS OF LIGHT TO MODERATE SNOW.
THIS WILL BE THE APPETIZER TO WHAT IS ABOUT TO OCCUR WEST OF THE
DIVIDE FOR THE REMAINDER OF WEEKEND. THESE WINTRY DETAILS ARE
INTRODUCED IN THE LONG TERM DISCUSSION.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

THE BEGINNING OF THE LONG TERM MARKS THE ONSLAUGHT OF MOISTURE TO
WESTERN WYOMING FOR THE NEXT 36 HOURS.  AS NOTED BY THE PREVIOUS
SHIFT...A WINTER STORM WATCH IS CURRENTLY IN EFFECT FOR FAR WESTERN
WYOMING STARTING 800PM SATURDAY NIGHT...AND THEN INCLUDES THE
ABSAROKAS...WIND RIVERS...AND GREEN RIVER FOOTHILLS ZONES AT 1100PM.
THE WEST TO SOUTHWEST SATURATED FLOW WILL FIRST IMPACT THE WEST SIDE
OF THE TETONS AND SW PORTION OF YNP.  AFTER MIDNIGHT...THE INTENSITY
SHOULD INCREASE IN THE WESTERN MOUNTAINS AS THE LAPSE RATES INCREASE
ALONG WITH THE MID LEVEL FLOW AROUND 40 KNOTS.  THE MODELS ARE ALL
IN QUITE GOOD AGREEMENT WITH THE OVERALL STORM MOVEMENT AND
PRECIPITATION EXPECTATIONS.  FOR THE WESTERN MOUNTAINS...THE
OROGRAPHIC SNOW MODEL ESTIMATES 18-30 INCHES POTENTIAL SNOW ON THE
WESTERN SLOPES OF THE TETONS UNDER PRIME CONDITIONS.  THE
NEIGHBORING VALLEYS ARE LIKELY TO SEE 8-10 INCHES WITH 12-14 IN
LOCALLY FAVORABLE LOCATIONS LIKE MOOSE AND SMOOT. AS THE FLOW
BECOMES MORE WEST NORTHWEST LATER ON SUNDAY...THE MODELS ARE
INDICATING BETTER OROGRAPHICS ALONG THE SALT AND WYOMING RANGES AS
WELL AS INTO THE BONDURANT AND CORA AREAS.

THE GFS HOWEVER INDICATES MORE POTENTIAL FORCING WITH A STRONGER
SHORTWAVE TROUGH MOVING THROUGH MONTANA INTO THE NORTHERN PLAINS ON
SUNDAY.  THE RESULTING MID LEVEL BAROCLINIC BOUNDARY FROM SOUTHERN
MT INTO NE WY ALLOWS FOR ENHANCED PRECIPITATION IN THE NORTHERN BIG
HORN BASIN AND BIGHORN MOUNTAINS INTO JOHNSON COUNTY.  IF THIS
SITUATION PANS OUT WITH THE NORTHWEST FLOW...SOME MORE INTERESTING
HIGH SNOW AMOUNTS COULD OCCUR IN THE NORTHERN BIGHORNS AND ALONG THE
NORTH AND EAST SIDES OF THE BIG HORN BASIN.

THE ACCOMPANYING 120+ KNOT JET WITH THIS STORM SYSTEM WILL MAKE FOR
VERY INTERESTING CONDITIONS AT THE MID AND HIGHER ELEVATIONS.
MOUNTAIN TOP AND SLOPE WINDS ACROSS WESTERN WYOMING ARE LIKELY TO BE
WINDY THROUGHOUT THE PERIOD.  HAVE EVALUATED THE POTENTIAL FOR
STRONG WINDS IN THE CODY FOOTHILLS FROM SAT NIGHT INTO SUN MORN.
CROSS SECTIONS OF SEVERAL MODELS INDICATE AT THIS TIME THAT STRONGER
WINDS OF 50 KNOTS SHOULD STAY IN THE HIGHER ELEVATIONS OF THE
EASTERN ABSAROKAS WITH AROUND 30-40 KNOTS IN THE FOOTHILL
LOCATIONS.  AGREE WITH THE PREVIOUS SHIFT THAT WEST TO NORTHWEST
WIND WILL STRENGTHEN ON SUNDAY FROM DUBOIS INTO THE WIND RIVER
BASIN...AS WELL AS ACROSS SWEETWATER COUNTY INTO CENTRAL WYOMING.

BOTH THE GFS AND ECMWF MOVE THE SYSTEM INTO THE PLAINS BY MONDAY
NIGHT WITH RESIDUAL SHOWERS OVER EASTERN WYOMING MONDAY NIGHT.
WHILE BOTH MODELS DEVELOP THE RIDGE ACROSS THE WESTERN US ON
TUESDAY...THE GFS SOLUTION IS SHARPER...AND THE FLATTER ECMWF ALLOWS
OVER-THE-TOP MOISTURE AND WEAK ENERGY TO SLIDE INTO NW WY TUESDAY
NIGHT.  NOT CONFIDENT IN EITHER SOLUTION TO HAVE INDICATED SLIGHT
CHANCE OF SNOW IN THE FORECAST.  BOTH MODELS THEN BRING ANOTHER
PACIFIC TROUGH INTO OUR AREA LATE WEDNESDAY NIGHT INTO CHRISTMAS
DAY. THE ECMWF STILL DIGS THE SYSTEM FURTHER SOUTH THAN THE
GFS...YET IS SLIGHTLY FURTHER NORTH THAN 24 HOURS AGO.  THE GFS IS
KEEPING WITH A MORE OPEN PROGRESSIVE TROUGH THROUGH THE NORTHERN
ROCKIES.  AND THE PARALLEL GFS IS EVEN MORE PROGRESSIVE.  EITHER
WAY...A STORM WILL IMPACT WYOMING ON CHRISTMAS...BUT THERE IS MUCH
UNCERTAINTY AS TO THE PRECIPITATION...TEMPERATURE..AND WIND IMPACTS
AT THIS TIME DUE TO THE LOCATION AND TIMING DIFFERENCES.
REGARDLESS...FRIDAY LOOKS TO BE COLDER THAN EARLIER IN THE WEEK.

&&

.AVIATION.../06Z ISSUANCE/

INCREASING MOISTURE PER MODELS INTO WESTERN WYOMING THIS WEEKEND.
SNOW WILL INCREASE AND BECOME MODERATE TO HEAVY BY LATE SATURDAY.
THIS WILL RESULT IN MOUNTAIN OBSCURATION FOR ALL MOUNTAIN RANGES.
IN ADDITION...WESTERN VALLEYS WILL BECOME IFR SATURDAY NIGHT AND
REMAIN THAT WAY THROUGH SUNDAY WITH LOW STRATUS AND SNOW.

OUTSIDE OF THE WIND RIVER BASIN OF CENTRAL WYOMING...VFR CONDITIONS
CAN BE EXPECTED THIS WEEKEND EAST OF THE DIVIDE. WITH A TIGHTENING
PRESSURE GRADIENT WINDS WILL INCREASE SATURDAY...ESPECIALLY ACROSS
THE SOUTHWESTERN WIND CORRIDOR FROM KRKS TO KCPR.

FOG HAS YET TO FORM AS OF 5Z AT KLND AND KRIW. LOCAL MODELS STILL
INDICATE FOG TO FORM AFTER MIDNIGHT AND LAST INTO THE EARLY MORNING
ALTHOUGH NOT AS WIDESPREAD AS PREVIOUS NIGHTS. WILL HAVE TO BE
MONITORED HOWEVER.

&&

.FIRE WEATHER...

NO FIRE WEATHER CONCERNS OR ACTIVITIES SHOULD BE CONSIDERED THIS
WEEKEND. A POTENT WINTER STORM WILL MOVE INTO WESTERN WYOMING...
BRINGING MODERATE TO HEAVY SNOW BY SATURDAY NIGHT. IN FACT...A WINTER
STORM WATCH REMAINS IN EFFECT AND DETAILS ON THIS WATCH CAN BE
SEEN IN OUR WINTER WEATHER PRODUCT. WESTERLY SURFACE WIND WILL
ALSO INCREASE MOST LOCATIONS BY SATURDAY AFTERNOON. UNSETTLED
WEATHER WITH SNOW AND VERY GUSTY WIND WILL CONTINUE ACROSS WEST
CENTRAL WYOMING ON SUNDAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ002-014-015-025.

WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ001-012-013-023-024.

DENSE FOG ADVISORY FROM 8 PM THIS EVENING TO 8 AM MST SATURDAY
WYZ017-018.

&&

$$

SHORT TERM...KPL
LONG TERM...MCDONALD
AVIATION...HATTINGS
FIRE WEATHER...KPL








000
FXUS65 KRIW 192156
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
256 PM MST FRI DEC 19 2014


.SHORT TERM...TONIGHT THROUGH SATURDAY

IMPRESSIVE WEEK FOR FOG ACROSS PARTS OF THE WIND RIVER BASIN OF
WEST CENTRAL WYOMING. THE ENVIRONMENT IS STILL CONDUSIVE FOR
FREEZING FOG TO CONTINUE ONE MORE NIGHT...ESPECIALLY NEAR
RIVERTON. IT MAY NOT BE AS WIDESPREAD AS PAST FEW NIGHTS.
NONETHELESS...WILL REISSUE DENSE FOG ADVISORY UNTIL 8 AM MST
SATURDAY MORNING. THINKING IS THAT MORE WESTERLY FLOW ABOVE THE
SURFACE AND WEAK SHORTWAVE ALOFT WILL HELP ERODE ALL FOG/LOW
STRATUS BY MID MORNING SATURDAY. EXPECT UNLIMITED VISIBILITY BY
SATURDAY AFTERNOON.

OTHERWISE...SHORTWAVE RIDGING THIS EVENING GIVES WAY TO WESTERLY
FLOW ALOFT. THIS FLOW ALOFT WILL INCREASE DURING THE DAY SATURDAY.
ISENTROPIC LIFT OVER FAR WESTERN MOUNTAINS THROUGH MUCH OF THE DAY
SATURDAY WILL RESULT IN AREAS OF LIGHT TO MODERATE SNOW.
THIS WILL BE THE APPETIZER TO WHAT IS ABOUT TO OCCUR WEST OF THE
DIVIDE FOR THE REMAINDER OF WEEKEND. THESE WINTERY DETAILS ARE
INTRODUCED IN THE LONG TERM DISCUSSION.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

THE BEGINNING OF THE LONG TERM MARKS THE ONSLAUGHT OF MOISTURE TO
WESTERN WYOMING FOR THE NEXT 36 HOURS.  AS NOTED BY THE PREVIOUS
SHIFT...A WINTER STORM WATCH IS CURRENTLY IN EFFECT FOR FAR WESTERN
WYOMING STARTING 800PM SATURDAY NIGHT...AND THEN INCLUDES THE
ABSAROKAS...WIND RIVERS...AND GREEN RIVER FOOTHILLS ZONES AT 1100PM.
THE WEST TO SOUTHWEST SATURATED FLOW WILL FIRST IMPACT THE WEST SIDE
OF THE TETONS AND SW PORTION OF YNP.  AFTER MIDNIGHT...THE INTENSITY
SHOULD INCREASE IN THE WESTERN MOUNTAINS AS THE LAPSE RATES INCREASE
ALONG WITH THE MID LEVEL FLOW AROUND 40 KNOTS.  THE MODELS ARE ALL
IN QUITE GOOD AGREEMENT WITH THE OVERALL STORM MOVEMENT AND
PRECIPITATION EXPECTATIONS.  FOR THE WESTERN MOUNTAINS...THE
OROGRAPHIC SNOW MODEL ESTIMATES 18-30 INCHES POTENTIAL SNOW ON THE
WESTERN SLOPES OF THE TETONS UNDER PRIME CONDITIONS.  THE
NEIGHBORING VALLEYS ARE LIKELY TO SEE 8-10 INCHES WITH 12-14 IN
LOCALLY FAVORABLE LOCATIONS LIKE MOOSE AND SMOOT. AS THE FLOW
BECOMES MORE WEST NORTHWEST LATER ON SUNDAY...THE MODELS ARE
INDICATING BETTER OROGRAPHICS ALONG THE SALT AND WYOMING RANGES AS
WELL AS INTO THE BONDURANT AND CORA AREAS.

THE GFS HOWEVER INDICATES MORE POTENTIAL FORCING WITH A STRONGER
SHORTWAVE TROUGH MOVING THROUGH MONTANA INTO THE NORTHERN PLAINS ON
SUNDAY.  THE RESULTING MID LEVEL BAROCLINIC BOUNDARY FROM SOUTHERN
MT INTO NE WY ALLOWS FOR ENHANCED PRECIPITATION IN THE NORTHERN BIG
HORN BASIN AND BIGHORN MOUNTAINS INTO JOHNSON COUNTY.  IF THIS
SITUATION PANS OUT WITH THE NORTHWEST FLOW...SOME MORE INTERESTING
HIGH SNOW AMOUNTS COULD OCCUR IN THE NORTHERN BIGHORNS AND ALONG THE
NORTH AND EAST SIDES OF THE BIG HORN BASIN.

THE ACCOMPANYING 120+ KNOT JET WITH THIS STORM SYSTEM WILL MAKE FOR
VERY INTERESTING CONDITIONS AT THE MID AND HIGHER ELEVATIONS.
MOUNTAIN TOP AND SLOPE WINDS ACROSS WESTERN WYOMING ARE LIKELY TO BE
WINDY THROUGHOUT THE PERIOD.  HAVE EVALUATED THE POTENTIAL FOR
STRONG WINDS IN THE CODY FOOTHILLS FROM SAT NIGHT INTO SUN MORN.
CROSS SECTIONS OF SEVERAL MODELS INDICATE AT THIS TIME THAT STRONGER
WINDS OF 50 KNOTS SHOULD STAY IN THE HIGHER ELEVATIONS OF THE
EASTERN ABSAROKAS WITH AROUND 30-40 KNOTS IN THE FOOTHILL
LOCATIONS.  AGREE WITH THE PREVIOUS SHIFT THAT WEST TO NORTHWEST
WIND WILL STRENGTHEN ON SUNDAY FROM DUBOIS INTO THE WIND RIVER
BASIN...AS WELL AS ACROSS SWEETWATER COUNTY INTO CENTRAL WYOMING.

BOTH THE GFS AND ECMWF MOVE THE SYSTEM INTO THE PLAINS BY MONDAY
NIGHT WITH RESIDUAL SHOWERS OVER EASTERN WYOMING MONDAY NIGHT.
WHILE BOTH MODELS DEVELOP THE RIDGE ACROSS THE WESTERN US ON
TUESDAY...THE GFS SOLUTION IS SHARPER...AND THE FLATTER ECMWF ALLOWS
OVER-THE-TOP MOISTURE AND WEAK ENERGY TO SLIDE INTO NW WY TUESDAY
NIGHT.  NOT CONFIDENT IN EITHER SOLUTION TO HAVE INDICATED SLIGHT
CHANCE OF SNOW IN THE FORECAST.  BOTH MODELS THEN BRING ANOTHER
PACIFIC TROUGH INTO OUR AREA LATE WEDNESDAY NIGHT INTO CHRISTMAS
DAY. THE ECMWF STILL DIGS THE SYSTEM FURTHER SOUTH THAN THE
GFS...YET IS SLIGHTLY FURTHER NORTH THAN 24 HOURS AGO.  THE GFS IS
KEEPING WITH A MORE OPEN PROGRESSIVE TROUGH THROUGH THE NORTHERN
ROCKIES.  AND THE PARALLEL GFS IS EVEN MORE PROGRESSIVE.  EITHER
WAY...A STORM WILL IMPACT WYOMING ON CHRISTMAS...BUT THERE IS MUCH
UNCERTAINTY AS TO THE PRECIPITATION...TEMPERATURE..AND WIND IMPACTS
AT THIS TIME DUE TO THE LOCATION AND TIMING DIFFERENCES.
REGARDLESS...FRIDAY LOOKS TO BE COLDER THAN EARLIER IN THE WEEK.

&&

.AVIATION.../00Z ISSUANCE/

INCREASING MOISTURE PER MODELS INTO WESTERN WYOMING THIS WEEKEND.
SNOW WILL INCREASE AND BECOME MODERATE TO HEAVY BY LATE SATURDAY.
THIS WILL RESULT IN MOUNTAIN OBSCURATION FOR ALL MOUNTAIN RANGES.
IN ADDITION...WESTERN VALLEYS WILL BECOME IFR SATURDAY NIGHT AND
REMAIN THAT WAY THROUGH SUNDAY WITH LOW STRATUS AND SNOW.

OUTSIDE OF THE WIND RIVER BASIN OF CENTRAL WYOMING...VFR CONDITIONS
CAN BE EXPECTED THIS WEEKEND EAST OF THE DIVIDE. GRADIENT WILL
INCREASE ALOFT BY SATURDAY AFTERNOON FOR BREEZY TO WINDY
CONDITIONS MOST AREAS.

WILL CONTINUE TO WATCH FOG AROUND KRIW TONIGHT. ANY REMAINING FOG
SHOULD DISSIPATE BY LATE SATURDAY MORNING. UNTIL THEN...WILL KEEP
MENTION OF FREEZING FOG IN KRIW TAF. KLND COULD GET CLOSE LATER THIS
EVENING AS WELL...WILL MONITOR.

&&

.FIRE WEATHER...

NO FIRE WEATHER CONCERNS OR ACTIVITIES SHOULD BE CONSIDERED THIS
WEEKEND. A POTENT WINTER STORM WILL MOVE INTO WESTERN WYOMING...
BRINGING MODERATE TO HEAVY SNOW BY SATURDAY NIGHT. IN FACT...A WINTER
STORM WATCH REMAINS IN EFFECT AND DETAILS ON THIS WATCH CAN BE
SEEN IN OUR WINTER WEATHER PRODUCT. WESTERLY SURFACE WIND WILL
ALSO INCREASE MOST LOCATIONS BY SATURDAY AFTERNOON. UNSETTLED
WEATHER WITH SNOW AND VERY GUSTY WIND WILL CONTINUE ACROSS WEST
CENTRAL WYOMING ON SUNDAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ002-014-015-025.

WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ001-012-013-023-024.

DENSE FOG ADVISORY FROM 8 PM THIS EVENING TO 8 AM MST SATURDAY
WYZ017-018.

&&

$$

SHORT TERM...KPL
LONG TERM...MCDONALD
AVIATION...KPL
FIRE WEATHER...KPL






000
FXUS65 KRIW 192156
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
256 PM MST FRI DEC 19 2014


.SHORT TERM...TONIGHT THROUGH SATURDAY

IMPRESSIVE WEEK FOR FOG ACROSS PARTS OF THE WIND RIVER BASIN OF
WEST CENTRAL WYOMING. THE ENVIRONMENT IS STILL CONDUSIVE FOR
FREEZING FOG TO CONTINUE ONE MORE NIGHT...ESPECIALLY NEAR
RIVERTON. IT MAY NOT BE AS WIDESPREAD AS PAST FEW NIGHTS.
NONETHELESS...WILL REISSUE DENSE FOG ADVISORY UNTIL 8 AM MST
SATURDAY MORNING. THINKING IS THAT MORE WESTERLY FLOW ABOVE THE
SURFACE AND WEAK SHORTWAVE ALOFT WILL HELP ERODE ALL FOG/LOW
STRATUS BY MID MORNING SATURDAY. EXPECT UNLIMITED VISIBILITY BY
SATURDAY AFTERNOON.

OTHERWISE...SHORTWAVE RIDGING THIS EVENING GIVES WAY TO WESTERLY
FLOW ALOFT. THIS FLOW ALOFT WILL INCREASE DURING THE DAY SATURDAY.
ISENTROPIC LIFT OVER FAR WESTERN MOUNTAINS THROUGH MUCH OF THE DAY
SATURDAY WILL RESULT IN AREAS OF LIGHT TO MODERATE SNOW.
THIS WILL BE THE APPETIZER TO WHAT IS ABOUT TO OCCUR WEST OF THE
DIVIDE FOR THE REMAINDER OF WEEKEND. THESE WINTERY DETAILS ARE
INTRODUCED IN THE LONG TERM DISCUSSION.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

THE BEGINNING OF THE LONG TERM MARKS THE ONSLAUGHT OF MOISTURE TO
WESTERN WYOMING FOR THE NEXT 36 HOURS.  AS NOTED BY THE PREVIOUS
SHIFT...A WINTER STORM WATCH IS CURRENTLY IN EFFECT FOR FAR WESTERN
WYOMING STARTING 800PM SATURDAY NIGHT...AND THEN INCLUDES THE
ABSAROKAS...WIND RIVERS...AND GREEN RIVER FOOTHILLS ZONES AT 1100PM.
THE WEST TO SOUTHWEST SATURATED FLOW WILL FIRST IMPACT THE WEST SIDE
OF THE TETONS AND SW PORTION OF YNP.  AFTER MIDNIGHT...THE INTENSITY
SHOULD INCREASE IN THE WESTERN MOUNTAINS AS THE LAPSE RATES INCREASE
ALONG WITH THE MID LEVEL FLOW AROUND 40 KNOTS.  THE MODELS ARE ALL
IN QUITE GOOD AGREEMENT WITH THE OVERALL STORM MOVEMENT AND
PRECIPITATION EXPECTATIONS.  FOR THE WESTERN MOUNTAINS...THE
OROGRAPHIC SNOW MODEL ESTIMATES 18-30 INCHES POTENTIAL SNOW ON THE
WESTERN SLOPES OF THE TETONS UNDER PRIME CONDITIONS.  THE
NEIGHBORING VALLEYS ARE LIKELY TO SEE 8-10 INCHES WITH 12-14 IN
LOCALLY FAVORABLE LOCATIONS LIKE MOOSE AND SMOOT. AS THE FLOW
BECOMES MORE WEST NORTHWEST LATER ON SUNDAY...THE MODELS ARE
INDICATING BETTER OROGRAPHICS ALONG THE SALT AND WYOMING RANGES AS
WELL AS INTO THE BONDURANT AND CORA AREAS.

THE GFS HOWEVER INDICATES MORE POTENTIAL FORCING WITH A STRONGER
SHORTWAVE TROUGH MOVING THROUGH MONTANA INTO THE NORTHERN PLAINS ON
SUNDAY.  THE RESULTING MID LEVEL BAROCLINIC BOUNDARY FROM SOUTHERN
MT INTO NE WY ALLOWS FOR ENHANCED PRECIPITATION IN THE NORTHERN BIG
HORN BASIN AND BIGHORN MOUNTAINS INTO JOHNSON COUNTY.  IF THIS
SITUATION PANS OUT WITH THE NORTHWEST FLOW...SOME MORE INTERESTING
HIGH SNOW AMOUNTS COULD OCCUR IN THE NORTHERN BIGHORNS AND ALONG THE
NORTH AND EAST SIDES OF THE BIG HORN BASIN.

THE ACCOMPANYING 120+ KNOT JET WITH THIS STORM SYSTEM WILL MAKE FOR
VERY INTERESTING CONDITIONS AT THE MID AND HIGHER ELEVATIONS.
MOUNTAIN TOP AND SLOPE WINDS ACROSS WESTERN WYOMING ARE LIKELY TO BE
WINDY THROUGHOUT THE PERIOD.  HAVE EVALUATED THE POTENTIAL FOR
STRONG WINDS IN THE CODY FOOTHILLS FROM SAT NIGHT INTO SUN MORN.
CROSS SECTIONS OF SEVERAL MODELS INDICATE AT THIS TIME THAT STRONGER
WINDS OF 50 KNOTS SHOULD STAY IN THE HIGHER ELEVATIONS OF THE
EASTERN ABSAROKAS WITH AROUND 30-40 KNOTS IN THE FOOTHILL
LOCATIONS.  AGREE WITH THE PREVIOUS SHIFT THAT WEST TO NORTHWEST
WIND WILL STRENGTHEN ON SUNDAY FROM DUBOIS INTO THE WIND RIVER
BASIN...AS WELL AS ACROSS SWEETWATER COUNTY INTO CENTRAL WYOMING.

BOTH THE GFS AND ECMWF MOVE THE SYSTEM INTO THE PLAINS BY MONDAY
NIGHT WITH RESIDUAL SHOWERS OVER EASTERN WYOMING MONDAY NIGHT.
WHILE BOTH MODELS DEVELOP THE RIDGE ACROSS THE WESTERN US ON
TUESDAY...THE GFS SOLUTION IS SHARPER...AND THE FLATTER ECMWF ALLOWS
OVER-THE-TOP MOISTURE AND WEAK ENERGY TO SLIDE INTO NW WY TUESDAY
NIGHT.  NOT CONFIDENT IN EITHER SOLUTION TO HAVE INDICATED SLIGHT
CHANCE OF SNOW IN THE FORECAST.  BOTH MODELS THEN BRING ANOTHER
PACIFIC TROUGH INTO OUR AREA LATE WEDNESDAY NIGHT INTO CHRISTMAS
DAY. THE ECMWF STILL DIGS THE SYSTEM FURTHER SOUTH THAN THE
GFS...YET IS SLIGHTLY FURTHER NORTH THAN 24 HOURS AGO.  THE GFS IS
KEEPING WITH A MORE OPEN PROGRESSIVE TROUGH THROUGH THE NORTHERN
ROCKIES.  AND THE PARALLEL GFS IS EVEN MORE PROGRESSIVE.  EITHER
WAY...A STORM WILL IMPACT WYOMING ON CHRISTMAS...BUT THERE IS MUCH
UNCERTAINTY AS TO THE PRECIPITATION...TEMPERATURE..AND WIND IMPACTS
AT THIS TIME DUE TO THE LOCATION AND TIMING DIFFERENCES.
REGARDLESS...FRIDAY LOOKS TO BE COLDER THAN EARLIER IN THE WEEK.

&&

.AVIATION.../00Z ISSUANCE/

INCREASING MOISTURE PER MODELS INTO WESTERN WYOMING THIS WEEKEND.
SNOW WILL INCREASE AND BECOME MODERATE TO HEAVY BY LATE SATURDAY.
THIS WILL RESULT IN MOUNTAIN OBSCURATION FOR ALL MOUNTAIN RANGES.
IN ADDITION...WESTERN VALLEYS WILL BECOME IFR SATURDAY NIGHT AND
REMAIN THAT WAY THROUGH SUNDAY WITH LOW STRATUS AND SNOW.

OUTSIDE OF THE WIND RIVER BASIN OF CENTRAL WYOMING...VFR CONDITIONS
CAN BE EXPECTED THIS WEEKEND EAST OF THE DIVIDE. GRADIENT WILL
INCREASE ALOFT BY SATURDAY AFTERNOON FOR BREEZY TO WINDY
CONDITIONS MOST AREAS.

WILL CONTINUE TO WATCH FOG AROUND KRIW TONIGHT. ANY REMAINING FOG
SHOULD DISSIPATE BY LATE SATURDAY MORNING. UNTIL THEN...WILL KEEP
MENTION OF FREEZING FOG IN KRIW TAF. KLND COULD GET CLOSE LATER THIS
EVENING AS WELL...WILL MONITOR.

&&

.FIRE WEATHER...

NO FIRE WEATHER CONCERNS OR ACTIVITIES SHOULD BE CONSIDERED THIS
WEEKEND. A POTENT WINTER STORM WILL MOVE INTO WESTERN WYOMING...
BRINGING MODERATE TO HEAVY SNOW BY SATURDAY NIGHT. IN FACT...A WINTER
STORM WATCH REMAINS IN EFFECT AND DETAILS ON THIS WATCH CAN BE
SEEN IN OUR WINTER WEATHER PRODUCT. WESTERLY SURFACE WIND WILL
ALSO INCREASE MOST LOCATIONS BY SATURDAY AFTERNOON. UNSETTLED
WEATHER WITH SNOW AND VERY GUSTY WIND WILL CONTINUE ACROSS WEST
CENTRAL WYOMING ON SUNDAY.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ002-014-015-025.

WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ001-012-013-023-024.

DENSE FOG ADVISORY FROM 8 PM THIS EVENING TO 8 AM MST SATURDAY
WYZ017-018.

&&

$$

SHORT TERM...KPL
LONG TERM...MCDONALD
AVIATION...KPL
FIRE WEATHER...KPL





000
FXUS65 KRIW 191821
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1121 AM MST FRI DEC 19 2014

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT

ANOTHER FOGGY MORNING ACROSS CENTRAL WYOMING...WITH A DENSE FOG
ADVISORY REMAINING FOR PORTIONS OF THE WIND RIVER BASIN.
MEANWHILE...LIGHT SNOW WILL CONTINUE ACROSS THE WESTERN MOUNTAINS AS
A DIRTY RIDGE MOVES THROUGH THE INTERMOUNTAIN WEST. SNOWFALL ACROSS
THE WEST MAY WEAKEN SLIGHTLY DURING THE AFTERNOON HOURS
TODAY...THOUGH AN APPROACHING TROUGH OF LOW PRESSURE WILL BRING THE
RETURN OF SNOWFALL ACROSS THE AREA. THE APPROACHING TROUGH WILL HIT
QUICKLY AND THEN MOVE OFF. HOWEVER...ANOTHER ROUND ON WINTRY WEATHER
WILL IMPACT THE AREA SOON AFTER ITS DEPARTURE. FOG MAY AGAIN DEVELOP
ACROSS CENTRAL FREMONT COUNTY OVERNIGHT WITH LIGHT WIND EXPECTED.

A STRONGER PUSH OF MOISTURE WILL MOVE OVER THE WESTERN MOUNTAINS AND
VALLEYS LATE SATURDAY NIGHT. WIDESPREAD SNOWFALL IS EXPECTED DURING
THE OVERNIGHT HOURS...WITH ACTIVITY REMAINING CONFINED TO THE
WESTERN MOUNTAINS AND VALLEYS. SNOWFALL...WHICH MAY BE HEAVY AT
TIMES...WILL CONTINUE THROUGH SUNDAY NIGHT...WORKING TO TAPER OFF
MONDAY MORNING. MODELS IN FAIR AGREEMENT WITH THIS PROGRESSION OF
THE STORM...WITH SOME MINOR TIMING DIFFERENCES NOTED. SNOWFALL WILL
MOVE EAST OF THE DIVIDE EARLY SUNDAY MORNING...THOUGH SNOWFALL
ACROSS THE LOWER ELEVATIONS IS NOT CURRENTLY EXPECTED TO BE
SIGNIFICANT. BY THE TIME SNOWFALL WEAKENS ON MONDAY MORNING...TOTAL
SNOWFALL ACCUMULATIONS MAY BE 5 TO 10 INCHES ACROSS THE IMPACTED
VALLEYS...WITH 1 TO 2 FEET OF SNOW POSSIBLE IN THE MOUNTAINS.
NATIONAL GUIDANCE SUPPORTS THOSE TOTALS...AND WITH THE CONSISTENCY
THE MODELS HAVE HAD THIS THIS SYSTEM...HAVE GONE AHEAD AND ISSUED A
WINTER STORM WATCH. SOME MINOR START TIME DIFFERENCES EXIST AS SNOW
SPREADS EASTWARD.

.LONG TERM...MONDAY THROUGH FRIDAY

SNOW TO CONTINUE INTO MONDAY MORNING BEFORE DECREASING THE
REMAINDER OF THE DAY. STRONG COLD FRONT BLASTING ACROSS AREAS EAST
OF THE DIVIDE WILL PRODUCE AREAS OF STRONG TO HIGH
WINDS...ESPECIALLY IN WEST TO NORTHWEST FAVORED AREAS. THE BEST
AREAS ON THE GFS AT LEAST APPEAR TO BE THE I80 CORRIDOR BUT
DETAILS ARE STILL CHANGING WITH EACH MODEL RUN. ALL EYES THEN
TURN TOWARDS OUR POTENTIAL CHRISTMAS SNOWSTORM. MODELS CONTINUE TO
CHANGE WITH EACH RUN. TONIGHT`S OP GFS AND ECMWF ARE VASTLY
DIFFERENT. THEY BOTH INDICATE SNOW ON CHRISTMAS BUT THE EVOLUTION
AND TYPE OF STORM ARE COMPLETELY DIFFERENT. THE GFS DIVES AN
MAINLY OPEN WAVE SE ACROSS US WITH MUCH MORE IMPRESSIVE
FRONTOGENESIS ACROSS THE NORTH HALF PUTTING PARTS OF FREMONT AND
NATRONA IN VERY FAVORABLE SRN END OF THAT ZONE WITH MID LEVEL
DEFORMATION OVERLYING THAT AREA. THE BIG DIFFERENCE IS THE
COMPLETE RECOVERY OF THE COLD AIR THAT COMES IN WITH OUR EARLY
WEEK SYSTEM WITH MID LEVEL TEMPERATURES REBOUNDING TO ONLY
SLIGHTLY BELOW ZERO AT H7 WHEREAS YESTERDAY THEY STAYED AROUND
-10C OR SO BEFORE THE CHRISTMAS STORM MOVED IN. THE ECMWF ALSO HAS
RIDGING MOVING IN AHEAD OF ITS CHRISTMAS DAY STORM BUT IT IS
SLOWER AND MUCH MORE IMPRESSIVE WITH A CLOSED OFF SYSTEM THAT
STRENGTHENS OVER SRN IDAHO ON CHRISTMAS DAY AND THEN TRACKS
SLOWLY ACROSS SRN WYO AND NRN COLORADO CHRISTMAS NIGHT. THE MAIN
NEGATIVE ON THE ECMWF IS THE AMOUNT OF COLD AIR IT POURS SWD IN
THE EARLY STAGES OF THE STORM. NOT SURE IT WOULD BE THAT COLD THAT
EARLY PLUS THE DYNAMICS OF THE ECMWF UPPER LOW POSITION WOULD
LIKELY BE QUITE IMPRESSIVE. ECMWF HAS A VERY STRONG 986MB SFC LOW
DEVELOPING OVER NERN CO ON CHRISTMAS DAY. DETAILS ARE STILL
UNCERTAIN ATTM BUT IT STILL LOOKS LIKE WE ARE ON TRACK FOR SNOW ON
CHRISTMAS DAY ACROSS MUCH OF THE AREA...ESPECIALLY ALONG AND EAST
OF THE DIVIDE. HOW MUCH AND THE EXACT TIMING WILL HAVE TO BE
DETERMINED AS WE GET CLOSER. IT IS STILL 6 DAYS AWAY! CURRENT
FORECAST IS A TIMING BLEND OF THE GFS AND ECMWF BUT STILL THINK
THAT SLOWER WILL PROBABLY BE A LITTLE BETTER BUT NOT AN ABSOLUTE
WITH A POTENTIAL UPSTREAM KICKER SHORTWAVE. WILL LINGER AT LEAST
CHANCE POPS THROUGH CHRISTMAS NIGHT BEFORE HAVING TO DEAL WITH OUR
UPSTREAM DISTURBANCE FRIDAY INTO FRIDAY NIGHT IN THE WEST AND
POSSIBLY SOUTH. QUITE CHILLY BEHIND OUR CHRISTMAS STORM SINGLE DIGITS
ABOVE TO SINGLE DIGITS BELOW IN THE FORECAST FOR STARTERS. STAY
TUNED OVER THE NEXT COUPLE DAYS AS THE DETAILS OF THE TRAVEL
IMPACTING STORM NOT ONLY THIS WEEKEND BUT CHRISTMAS DAY BEFORE
MORE CERTAIN.

&&

.AVIATION.../18Z ISSUANCE/

LOW LEVEL FOG CONTINUES TO PERSIST NEAR KRIW. STILL LOOKING AT THE
POTENTIAL FOR THIS FOG TO DEEPEN AGAIN THIS EVENING. THEREFORE...
LOCALIZED IFR CONDITIONS DUE TO SOME FOG AND LOW CLOUDS AFTER 00Z
SATURDAY. OTHERWISE...EXPECT VFR CONDITIONS THROUGH TONIGHT WITH SOME
MID/HIGH LEVEL CLOUD COVER OVER WEST CENTRAL WYOMING. SOME MOUNTAIN
OBSCURATION CAN ALSO BE EXPECTED WEST OF THE DIVIDE THRU EARLY SATURDAY.

&&

.FIRE WEATHER...

GUSTY WIND EXPECTED DURING THE AFTERNOON HOURS ACROSS THE WIND
CORRIDOR BETWEEN ROCK SPRINGS AND CASPER...AND ALONG THE LEE SIDE OF
THE MOUNTAINS. PERIODS OF SNOWFALL WILL CONTINUE ACROSS WESTERN
WYOMING WITH LINGERING MOISTURE. AN APPROACHING SYSTEM MAY
POTENTIALLY BRING SIGNIFICANT SNOWFALL ACROSS THE WESTERN MOUNTAINS
AND VALLEYS STARTING LATE SATURDAY...AND CONTINUING INTO MONDAY
MORNING. SOME SNOWFALL WILL MOVE EAST OF THE CONTINENTAL
DIVIDE...THOUGH SNOWFALL ACCUMULATIONS EAST OF THE DIVIDE ARE STILL
LOOKING TO BE BELOW HIGHLIGHT THRESHOLDS. WESTERN WYOMING...HOWEVER...
HAS A WINTER STORM WATCH ISSUED. DETAILS ON POTENTIAL TIMING AND
INTENSITY CAN BE SEEN IN OUR WINTER WEATHER PRODUCT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ002-014-015-025.

WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY MORNING
WYZ001-012-013-023-024.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...SKRBAC
AVIATION...KPL
FIRE WEATHER...BRANHAM






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