727
FXUS65 KRIW 181754
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1054 AM MST WED DEC 18 2024
KEY MESSAGES
- BREEZY TO WINDY CONDITIONS EXPECTED FOR THE AREA WITH HIGH
WIND LIKELY IN THE NORMALLY WIND PRONE AREAS.
- MILD AND TRANQUIL WEATHER RETURNS FROM THURSDAY THROUGH
SATURDAY.
- THE NEXT CHANCE OF SNOW RETURNS TO WESTERN WYOMING SATURDAY
NIGHT INTO SUNDAY.
DISCUSSION
ISSUED AT 127 AM MST WED DEC 18 2024
LET'S PLAY A LITTLE JEOPARDY THIS MORNING. THE ANSWER IS, WHAT IS
WYOMING FAMOUS FOR AND ALSO STARTS WITH W? (CUE THE FINAL JEOPARDY
MUSIC). IF YOU YOUR ANSWER IS: WHAT IS WIND? YOU ARE CORRECT AND YOU
WIN WHAT YOU BET. HOPE YOU PHRASED IT IN THE FORM OF A
QUESTION.
ANYWAY, THAT LOOKS TO BE THE MAIN CONCERN TODAY. WE HAVE A DECENT
SET UP FOR HIGH WIND ACROSS FAVORED PORTIONS OF THE AREA. WE WILL
HAVE A SHORTWAVE MOVING ACROSS THE AREA THIS AFTERNOON. WE WILL HAVE
A DECENT 16 MILLIBAR PRESSURE GRADIENT ACROSS THE STATE FROM WEST TO
EAST. AND, MUCH OF THE AREA WILL BE UNDER THE RIGHT FRONT QUADRANT
OF AN 120 KNOT JET STREAK TO ENHANCE DOWNWARD MOMENTUM. MOST
GUIDANCE IS ALSO GIVING 50 TO 60 KNOT WINDS AT 700 MILLIBARS THAT
THE JET WILL HELP TO FORCE TO THE GROUND. THE SET UP LOOKS RATHER
FAVORABLE FOR THE CODY FOOTHILLS, WHERE PROBABILISTIC GUIDANCE GIVES
A GREATER THAN 4 OUT OF 5 CHANCE OF WIND GUSTS PAST 55 MPH,
INCLUDING NEAR THE TOWN OF CODY AND ALONG HIGHWAY 120. WITH THIS, WE
UPGRADED THE HIGH WIND WATCHES TO WARNINGS HERE, WITH THE STRONGEST
WIND EXPECTED BETWEEN AROUND 2 PM TO 8 PM THEN DECREASING LATER AT
NIGHT.
WE ALSO HOISTED A HIGH WIND WARNING FOR THE WIND PRONE AREAS
AROUND CASPER AND THE GREEN MOUNTAINS. AREAL COVERAGE MAY BE MORE
RESTRICTED HERE. HOWEVER, SINCE MUCH OF THE CITY OF CASPER HAS AT
LEAST A 1 IN 2 CHANCE OF WIND GUSTS PAST 55 MPH WITH UP TO A 4 IN 5
CHANCE IN THE MORE WIND PRONE AREAS, LIKE WYOMING BOULEVARD AND NEAR
HAT SIX ROAD. WITH THE IMPACTS TO THESE MAIN TRANSPORTATION
CORRIDORS, WE DECIDED TO ISSUE. MANY AREAS WILL HAVE GUSTY WIND AS
WELL, BUT SHOULD FALL SHORT OF WARNING CRITERIA. I DO HAVE SOME
CONCERN FOR NORTHERN JOHNSON COUNTY AS WELL, MAINLY POST TROUGH HERE
WHEN NORTHWEST FLOW AND COLD ADVECTION KICK IN. THE GFS MOS GUIDANCE
HAS SUSTAINED 40 MPH WINDS TONIGHT. OTHER DETERMINISTIC GUIDANCE IS
NOT AS IMPRESSED THOUGH. PROBABILISTIC GUIDANCE ONLY GIVES A 1 OUT OF
10 CHANCE FOR WIND GUSTS PAST 50 MPH AS WELL. SO, NO HIGHLIGHTS HERE
FOR NOW ALTHOUGH WE MAY ISSUE A SPECIAL WEATHER STATEMENT. THE DAY
SHIFT WILL HAVE TO WATCH THIS THOUGH FOR ANY UPWARD TRENDS.
THE TROUGH WILL ALSO BRING SOME SNOW TO NORTHWESTERN WYOMING.
IMPACTS WILL BE LIMITED THOUGH. THE ONLY PLACE WITH AT LEAST A 2 OUT
OF 5 CHANCE OF 4 INCHES OR MORE IS SOUTHWESTERN YELLOWSTONE, AND
IMPACTS IN THIS AREA ARE BASICALLY NON EXISTENT THIS TIME OF YEAR.
FOLLOWING THIS, RIDGING WILL BUILD ACROSS THE AREA AND BRING ANOTHER
PERIOD OF DRY AND TRANQUIL WEATHER WITH ABOVE NORMAL TEMPERATURES
AND GENERALLY LIGHT TO MODERATE WIND THROUGH AT LEAST SATURDAY. THE
NEXT POTENTIAL WEATHER SYSTEM WILL MOVE IN SATURDAY NIGHT INTO
SUNDAY. THIS ONE THOUGH, LOOKS MUCH LIKE THE PREVIOUS SEVERAL
SYSTEMS, WITH A ZONAL FLOW AND ANY SNOW IMPACTING MAINLY WESTERN
WYOMING. THIS SYSTEM IS ALSO A QUICK HITTER AND AMOUNTS LOOK
MODERATE AT BEST. LOOKING OUT FOR THE CHANCE OF A WHITE CHRISTMAS,
THERE IS A CHANCE OF A SYSTEM COULD CROSS THE AREA AND BRING SOME
SNOW. HOWEVER, THIS IS STILL A WEEK OUT AND A LOT CAN CHANGE. IN
ADDITION, MODELS TEND TO HAVE A FAST BIAS THIS FAR OUT AND IT COULD
END UP ARRIVING THE DAY AFTER CHRISTMAS. STAY TUNED TO SEE IF THIS
COMES TO FRUITION.
AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 1053 AM MST WED DEC 18 2024
A SHORTWAVE TROUGH PUSHES THROUGH TODAY, WHICH WILL TIGHTEN THE
PRESSURE GRADIENT AND ALSO BRING A JET STREAK OVER THE REGION,
RESULTING IN STRONG DOWNSLOPING WINDS ON THE LEE SIDE OF THE
ABSAROKAS, BIGHORNS, AND CASPER MOUNTAIN. THUS, WIND WILL BE THE
MAIN AVIATION CONCERN THROUGH THE FIRST HALF OF THE PERIOD. GUSTS OF
40 TO 45KTS WILL BE COMMON AT KCOD AND KCPR THROUGH THE AFTERNOON
AND EVENING. LLWS AT KCOD UP TO 60 TO 65KTS IS ALSO POSSIBLE AFTER
22Z THIS AFTERNOON. THERE IS A 30% CHANCE THAT DOWNVALLEY
NORTHWESTERLY WINDS WILL PUSH INTO KRIW AFTER 00Z. SEVERAL MODELS,
MOST NOTABLY THE HRW FV3 ARE SHOWING INDICATIONS OF THIS, BUT IT
LOOKS AS THOUGH KRIW WILL BE JUST ON THE CUSP OF THE STRONGER WINDS,
AND THUS HAVE INCLUDED A TEMPO FOR A FEW HOURS WHEN THE MOST LIKELY
CHANCE OF SEEING THE DOWNVALLEY WINDS WILL OCCUR.
THE OTHER NOTABLE AVIATION CONCERN WILL BE FOG. THIS WILL BE A
CONCERN FOR ALL WEST OF THE DIVIDE TERMINALS AFTER 00Z THROUGH THE
END OF THE PERIOD. KPNA AND KRKS CURRENTLY ARE SEEING MVFR CIGS AS
LOW CLOUDS SIT OVER THE GREEN RIVER BASIN. THESE LOW CLOUDS WILL
LIKELY (70% CHANCE) STICK AROUND AND LOWER TOWARDS SUNSET TONIGHT,
BECOMING IFR/LIFR. KBPI HAS THE MOST LIKELY CHANCE (50%) FOR FOG,
WITH SEVERAL MODELS INDICATING CIGS DROPPING QUICKLY AFTER 00Z AND
STAYING AT FL001 TO FL002 THROUGH THE END OF THE PERIOD, RETURNING
TO VFR AROUND 18/19Z THURSDAY. INDICATIONS OF FOG AT KPNA AND KRKS
ARE SIMILAR, BUT LOOKS TO BE LATER ONSET (PERHAPS CLOSER TO 06-08Z).
FOR KRKS, BETTER CHANCES (80%) ARE FARTHER NORTH AND WEST
(FARSON/FONTENELLE) BUT THERE IS STILL A 30% CHANCE THAT FOG WILL
SPREAD FAR ENOUGH SOUTH AND EAST TO IMPACT THE TERMINAL. AT KJAC,
THERE IS ALSO A 30% CHANCE OF FOG, BUT MODEL INDICATIONS OF FOG ARE
NOT AS STRONG AS THEY ARE IN OTHER PORTIONS OF THE REGION. HAVE
INCLUDED VCFG AND FEW001/FEW002 GROUPS FOR WEST OF THE DIVIDE
TERMINALS THROUGH MUCH OF THE NIGHT, AS THERE IS NOT ENOUGH
CONFIDENCE IN FOG FOR A PREVAILING GROUP.
PLEASE SEE THE AVIATION WEATHER CENTER AND/OR CWSU ZDV AND ZLC FOR
THE LATEST INFORMATION ON ICING AND TURBULENCE FORECASTS.
RIW WATCHES/WARNINGS/ADVISORIES
HIGH WIND WARNING UNTIL 2 AM MST THURSDAY FOR WYZ002-003.
HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING FOR WYZ019-020.
DISCUSSION...HATTINGS
AVIATION...HENSLEY
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