Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 270936
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
236 AM MST THU NOV 27 2014

.SHORT TERM...THURSDAY THROUGH SATURDAY NIGHT

A MUCH QUIETER NIGHT ACROSS THE AREA TONIGHT THAN LAST NIGHT AS THE
SYSTEM THAT BROUGHT THE SNOW HAS EXITED WITH RIDGING OVER THE AREA
TODAY. HOWEVER...THIS IS WYOMING IN NOVEMBER SO SOMETHING ALWAYS HAS
TO BE GOING ON. FIRST IS THE FOG THAT HAS DEVELOPED IN SOME AREAS
WHERE THE MELTING SNOW TODAY AS SATURATED THE ATMOSPHERE. CONTINUITY
HAD PATCHY FOG SO WE LEFT IT. THE MAIN CONCERN TODAY IS WIND. THE
SENSOR AT CHIEF JOSEPH IS ALREADY REPORTING GUSTS TO AROUND 60 MPH.
THE MODELS SHOW WINDS OVER 50 KNOTS AT 700 MILLIBARS MOST OF THE DAY
ACROSS THE NORTHWESTERN MOUNTAINS. I HAVE MY DOUBTS THAT THE CODY
FOOTHILLS WOULD BLOW HIGH WIND DURING THE DAY TODAY AS THE WINDS MAY
HAVE TROUBLE MIXING DOWN. HOWEVER...WE WILL ISSUE THE UPGRADE THE
HIGH WIND WATCH TO A WARNING BUT MENTION THE STRONGEST WINDS WOULD
BE LATE TONIGHT. ELSEWHERE...THERE ARE SOME STRONG WINDS ALOFT OVER
THE AREA. HOWEVER...WITH HIGH CLOUDS OVER THE AREA MIXING SHOULD BE
FAIRLY LIMITED. NOW FOR HIGH TEMPERATURES...IT WILL BE WARMER TODAY
ALTHOUGH AREAS THAT RECEIVED A DECENT AMOUNT OF SNOW YESTERDAY WILL
BE COOLER. WE DON`T KNOW THE GFS MOS HAS BEEN SMOKING IN THE
RIVERTON AND LANDER AREAS. THEY ARE GIVING RIVERTON AND LANDER A
HIGH OF 72 DEGREES TODAY. DON`T KNOW HOW THAT WOULD HAPPEN WITH SOME
LEE ENHANCED CLOUDS AND NOT A LOT OF MIXING. EVEN IF WE DID FULLY
MIX...700 MILLIBAR TEMPERATURES ONLY GIVE A HIGH OF 60. SO...THAT
GUIDANCE WAS THROWN IN THE TRASH. OOPS...THIS IS 2014...I MEAN IN
THE RECYCLE BIN. AS FOR PRECIPITATION...THE MODELS ARE SHOWING A BIT
OF SNOW MAINLY ACROSS YELLOWSTONE LATE TONIGHT AND FRIDAY WITH SOME
LEFT FRONT JET ENERGY. HOWEVER...AMOUNTS ARE EXPECTED TO BE LIGHT.
AS FOR FRIDAY EAST OF THE DIVIDE..EXPECT ANOTHER MILD DAY. THERE
WILL BE SOME GUSTY WINDS ONCE AGAIN THOUGH...ESPECIALLY ACROSS THE
SOUTHWESTERN WIND CORRIDOR. AT THIS TIME...WE KEPT WINDS BELOW HIGH
WIND CRITERIA BUT IT WILL HAVE TO BE WATCHED. THIS MAY BE A WARMER DAY WITH
BETTER MIXING BUT ONCE AGAIN...THE NUMBERS IN THE 70S IN THE WIND
RIVER BASIN LOOK OVERDONE. THE STRONGEST WINDS ALOFT LOOK TO BE
FRIDAY NIGHT BUT THIS MAY LIMIT MIXING.

NOW FOR THE NEXT MAIN WEATHER MAKER. ANOTHER WEATHER MAKER WILL
APPROACH FROM THE WET AND BRING MORE SNOW TO THE WEST STARTING LATER
FRIDAY NIGHT. HOWEVER...THE MAIN EVENT LOOKS TO HOLD OFF UNTIL
SATURDAY AND SATURDAY NIGHT WHEN THE BEST MOISTURE AND JET DYNAMICS
WORK INTO THE AREA. SNOWFALL AMOUNTS IN CONTINUITY LOOKED REASONABLE
AT THIS TIME SO WE MADE FEW CHANGES. MEANWHILE...AREAS EAST OF THE
DIVIDE SHOULD SQUEEZE OUT ONE MORE MILD AND DRY DAY ALTHOUGH IT WILL
BE BREEZY TO WINDY AND DRY DAY. A COLD FRONT WILL THEN BEGIN
DROPPING INTO WYOMING FROM THE NORTH IN THE EVENING AND DROP ACROSS
MUCH OF THE AREA BY SUNDAY MORNING. THIS WILL USHER IN MUCH COLDER
TEMPERATURES. IT COULD ALSO BRING A PERIOD OF SNOW TO SOME AREAS.
HOWEVER...DETAILS ON HOW MUCH ARE STILL MUDDY AT THIS POINT. STAY
TUNED.

.LONG TERM...SUNDAY THROUGH THURSDAY

AN ARCTIC COLD FRONT SHOULD BE ALONG THE DIVIDE BY 12Z SUNDAY. THIS
FRONT IS EXPECTED TO MOVE VERY LITTLE SUNDAY...SEPARATING A BITTER
COLD AIR MASS EAST...WITH SEASONAL TO SLIGHTLY ABOVE AVERAGE TEMPS
WEST/SOUTHWEST. A SHORTWAVE TROUGH MOVING ACROSS THE NORTHERN
ROCKIES...AND A STRONG BAROCLINIC ZONE OVER THE FORECAST AREA WILL
GIVE A CHANCE OF SNOWFALL ACROSS MUCH OF THE AREA SUNDAY...GENERALLY
SHIFTING FROM NORTH TO SOUTH DURING THE DAY. LOOKS LIKE THE BEST
SNOWFALL CHANCES SHOULD BE BEST IN THE MORNING...BEFORE THE BULK OF
ENERGY FROM THE SHORTWAVE TROUGH EXITS INTO THE PLAINS...AND THE
BAROCLINIC ZONE OVER THE AREA WEAKENS/SLIDES SOUTH AND EAST. ALSO
MODELS ARE SHOWING AT SOME ISENTROPIC LIFT OVER THE ARCTIC AIR MASS
SUNDAY MORNING. DURING SUNDAY AFTERNOON INTO THE EVENING...MODELS
ARE HINTING AT A MOIST SHEAR AXIS REMAINING OVER THE SOUTHERN
PORTION OF THE FORECAST AREA...TRANSITIONING INTO A MODEST MOIST
WESTERLY FLOW DURING SUNDAY NIGHT.

ON MONDAY/MONDAY NIGHT...GLOBAL MODELS ARE IN DECENT AGREEMENT WITH
ANOTHER QUICK MOVING SHORTWAVE TROUGH PUSHING ACROSS THE EXTREME NORTHERN
ROCKIES INTO THE NORTHERN PLAINS. AHEAD OF THIS SHORTWAVE TROUGH...A
MOIST OROGRAPHIC FLOW SHOULD RESULT IN LIGHT TO PERHAPS MODERATE
SNOW OVER THE WEST MONDAY...WHILE A LEE TROUGH DEVELOPS HELPING TO
QUICKLY ERODE THE ARCTIC AIR MASS IN PLACE ON SUNDAY. SOME TRAPPED
BASINS EAST OF THE DIVIDE...ESPECIALLY THE EASTERN BIGHORN BASIN
MIGHT BE HARD PRESSED TO WARM UP...BUT TYPICAL MIXED AREAS SHOULD
WARM UP NICELY. THE ASSOCIATED COLD FRONT WITH THIS SYSTEM IS
EXPECTED TO PUSH ACROSS THE AREA LATE MONDAY NIGHT INTO TUESDAY
MORNING...BUT IS NOT NEARLY AS COLD AS THE ARCTIC FRONT SATURDAY NIGHT.
AHEAD OF THE FRONT MONDAY NIGHT...ANOTHER HIGH WIND EVENT COULD BE
SETTING UP OVER THE ABSAROKA MTS/CODY FOOTHILLS. THE MAIN DYNAMICS
AND BAROCLINIC ZONE WITH THIS SYSTEM IS FARTHER NORTH WITH THIS
SYSTEM RESULTING IN LESS OF A CHANCE OF PRECIPITATION EAST OF THE
DIVIDE...BUT THE NORTHWEST/WESTERN MOUNTAINS SHOULD SEE SOME SNOW
THROUGH TUESDAY MORNING.

THERE COULD BE A SMALL BREAK IN THE ACTION LATE TUESDAY/TUESDAY
NIGHT...BEFORE THE FOCUS TURNS TO A CLOSED UPPER LOW OVER THE
EASTERN PACIFIC. MODELS HAVE BEEN TRENDING TOWARD THIS UPPER LOW
MOVING INTO THE WEST COAST TUESDAY NIGHT/WEDNESDAY...AND BECOMING
AN OPEN WAVE IMPACTING THE ROCKIES IN THE WEDNESDAY/THURSDAY TIME
FRAME. HOWEVER...THERE REMAINS SOME MODELS THAT SHOW A RIDGE
DEVELOPING OVER THE ROCKIES WEDNESDAY AND THURSDAY...WITH THIS
UPPER LOW MAINLY IMPACTING THE PACIFIC NORTHWEST MID WEEK. WITH
THIS UNCERTAINTY WILL BROAD BRUSH SLIGHT VALLEY/CHANCE MTN POPS
OVER THE WEST/SOUTHWEST WHILE KEEPING AREAS EAST OF THE DIVIDE DRY
FOR NOW. THE PACIFIC NATURE OF THIS SYSTEM OR THE RIDGE BUILDING
OVER THE AREA WILL RESULT IN MAINLY ABOVE AVERAGE TEMPS FOR
WEDNESDAY AND THURSDAY.

&&

.AVIATION.../12Z ISSUANCE/

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

AREAS OF IFR/LIFR FOG OR LIFR CIGS WILL PERSIST ACROSS THE BIGHORN
BASIN THROUGH 16Z BEFORE SOME IMPROVEMENT IS EXPECTED.  THERE
SHOULD BE SOME EROSION OF THE FOG BANK ON THE WEST END...VCNTY AND
WEST KCOD...AS STRONGER DOWNSLOPE WINDS PROVIDE BETTER MIXING.

OTHERWISE VFR CONDITIONS WILL PREVAIL ACROSS THE REST OF THE AREA
WITH MUCH MORE PATCHY FOG PARTIALLY OBSCURING LOWER RIVER VALLEYS
THROUGH 18Z.  AREAS OF LLWS WILL BE ENCOUNTERED THROUGH THE
PERIOD...ESPECIALLY ALONG THE EAST SLOPES OF THE DIVIDE...VCNTY
KLND-KCOD...WHERE WINDS IN THE FL080-100 LAYER WILL BE
270/50-60KTS.  SOME OF THESE STRONGER WINDS WILL PUSH DOWN THE
FOOTHILLS INTO VCNTY KCOD-KDUB BY 00Z FRIDAY.

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

WINDS AT MOUNTAIN TOP LEVEL WILL INCREASE TO BETWEEN 50-60 KTS BY
SUNRISE THIS MORNING...RESULTING IN INCREASING TURBULENCE
THROUGH THE REST OF THE PERIOD.  THIS STRONG WESTERLY FLOW WILL ALSO
KEEP SOME HIGHER MTNS OBSCURED IN -SN WITH SOME LCL MVFR CIGS VCNTY
KJAC THROUGH THE PERIOD.

&&

.FIRE WEATHER...

WIDELY SCATTERED SHOWERS WILL LINGER OVER THE NORTHWEST TODAY.
TEMPERATURES WILL WARM AS WEST WINDS INCREASE ACROSS THE AREA. HIGH
WINDS WILL BECOME A THREAT EAST OF THE CONTINENTAL
DIVIDE...ESPECIALLY IN THE ABSAROKA MOUNTAINS INTO THE CODY
FOOTHILLS. IN THE VALLEYS AND BASINS ALONG RIVERS AND LAKES...AREAS
OF FOG WILL REMAIN INTO THIS MORNING BEFORE DISSIPATING. SNOW COVER
WILL REMAIN WIDESPREAD OVER MOST OF THE AREA WITH LOW FIRE WEATHER
CONCERNS. ANOTHER STORM WILL BRING MORE SNOW TO THE WEST FOR
SATURDAY. EXPECT MILD...DRY AND BREEZY TO WINDY WEATHER EAST OF THE
DIVIDE FRIDAY INTO SATURDAY.
&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM NOON TODAY TO 5 PM MST SATURDAY
WYZ002-003.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...WM
AVIATION...AEM
FIRE WEATHER...HATTINGS






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