919
FXUS65 KRIW 182245
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
345 PM MST WED DEC 18 2024
KEY MESSAGES
- HIGH WINDS ARE EXPECTED THIS AFTERNOON AND EVENING OVER THE
ABSAROKA MOUNTAINS AND CODY FOOTHILLS AS WELL AS FROM SOUTH
PASS EASTWARD INTO NATRONA COUNTY. WIND GUSTS 55-65 MPH CAN BE
EXPECTED WITH LOCALLY HIGHER GUSTS. BREEZY AND GUSTY WIND WILL
OCCUR IN OTHER AREAS FOR THIS TIME FRAME AS WELL.
- LIGHT SNOW SHOWERS OVER THE NORTHWEST WY MOUNTAINS WILL
DIMINISH AFTER MIDNIGHT, WITH HIGH PRESSURE SETTLING IN
THURSDAY THROUGH SATURDAY. ABOVE NORMAL TEMPERATURES WITH
GENERALLY SLIGHT WINDS AND PARTLY CLOUDY SKIES ARE EXPECTED.
- WEAK STORM SYSTEMS RETURN TO WESTERN WY EARLY SUNDAY MORNING,
MONDAY, AND CHRISTMAS DAY. NO MAJOR IMPACTS ARE EXPECTED AT
THIS TIME, THOUGH LIGHT TO MODERATE SNOWFALL MAY IMPACT
HOLIDAY TRAVEL.
DISCUSSION
ISSUED AT 100 PM MST WED DEC 18 2024
THE CURRENT WEATHER PATTERN INDICATES A SHORTWAVE TROUGH MOVING
IN WESTERLY FLOW THROUGH MONTANA AND NORTHERN WYOMING THIS
AFTERNOON AND EVENING. THE RESULTING TIGHTENED PRESSURE
GRADIENTS IN THE MID- AND LOWER-LEVELS ARE LEADING TO AN
INCREASE IN HIGH WIND POTENTIAL FOR THE ABSAROKA MOUNTAINS AND
CODY FOOTHILLS AS WELL AS ACROSS PORTIONS OF CENTRAL WYOMING.
THE EXISTING HIGH WIND WARNING IS HIGHLIGHTING THE POTENTIAL FOR
60-75 MPH WIND GUSTS IN THE HIGHER TERRAIN, WITH 55-65 GUSTS IN
THE LOWER ELEVATIONS OF THOSE AREAS. AS LIKE MUCH OF WYOMING,
LOCALLY AREAS NAY SEE ENHANCEMENTS, SUCH AS RED CANYON, CHIEF
JOSEPH PASS, OUTER DRIVE, ETC. BREEZY AND GUSTY WINDS ARE
EXPECTED ELSEWHERE, AND SHOULD CREATE BLOWING SNOW IN THE AREAS
WITH RECENT SNOWFALL. TEMPERATURES REMAIN ABOVE NORMAL AND LOOK
TO STAY ABOVE NORMAL FOR THE NEXT 7 DAYS AT LEAST.
AS THIS TROUGH MOVES INTO THE NORTHERN PLAINS EARLY THURSDAY
MORNING, COOL AND BREEZY NORTHWEST FLOW ON THE DOWNSTREAM BACK
EDGE OF A RIDGE WILL BE OVER THE FORECAST AREA. SHOWERS WILL
DIMINISH QUICKLY THU MORNING, THOUGH BREEZY AND GUSTY WEST-
NORTHWEST WINDS WILL MAKE IT FEEL COOL. OF NOTE AS WELL EARLY
THURSDAY MORNING IS THE POSSIBILITY OF FOG IN SOME WESTERN
VALLEYS. THE MOST LIKELY LOCATIONS ARE STAR VALLEY AND
COKEVILLE, WITH LESSER CHANCES AROUND JACKSON AND BIG
PINEY/PINEDALE. AS THE UPPER- LEVEL HIGH PRESSURE BUILDS OVER
THE WESTERN US THURSDAY, SKIES WILL BECOME MORE CLEAR FROM WEST
TO EAST, THOUGH UPPER-LEVEL CLOUDS SHOULD CONTINUE OVER WESTERN
AND NORTHERN WY. FRIDAY WILL SEE THE RIDGE MOVE EASTWARD TO THE
WY/ID BORDER WITH MORE CLOUDINESS OVER NORTHWEST WY.
TEMPERATURES WILL REMAIN WARM AND WINDS WILL BE ON THE LIGHTER
SIDE. SATURDAY WILL THEN SEE THE RIDGE AXIS MOVE OVER WY AND
THEN TO THE EAST AS A TROUGH DIGS ALONG THE WEST COAST. WINDS
WILL INCREASE AGAIN SATURDAY AS THE SURFACE PRESSURE GRADIENT
STRENGTHENS. BREEZY AND GUSTY WINDS CAN BE EXPECTED DURING THE
DAY IN THE TYPICAL AREAS FROM SOUTHWEST INTO CENTRAL WY. CLOUDS
WILL INCREASE DURING THE AFTERNOON OVER WESTERN WY DUE TO AN
INITIAL SHORTWAVE TROUGH MOVING INTO SW IDAHO.
THE MEDIUM-RANGE MODELS ARE INDICATING THAT THIS INITIAL
SHORTWAVE TROUGH WILL EJECT EASTWARD EARLY SUNDAY MORNING. AT
THIS TIME, THE PRECIPITATION FROM THIS SYSTEM LOOKS LIKE IT
SHOULD IMPACT NORTHWEST AND NORTHERN WY, WITH THE SOUTHERN AND
CENTRAL PARTS OF THE FORECAST AREA GETTING IMPACTED BY STRONG
GUSTY WEST WINDS. TEMPERATURES WILL TAKE A DROP ON SUNDAY AS A
RESULT, BUT STILL REMAIN SLIGHTLY ABOVE NORMAL. THE NEXT
SHORTWAVE TROUGH FROM THE SYSTEM WILL THEN PUSH INTO WESTERN WY
LATE SUNDAY NIGHT INTO MONDAY. AT THIS TIME, MODERATE SNOW
SHOULD IMPACT WESTERN AND SOUTHERN WY, KEEPING TEMPERATURES ON
THE COOL SIDE. AND LIKE THE PREVIOUS SYSTEM, LITTLE TO NO
PRECIPITATION IS EXPECTED EAST OF THE DIVIDE IN THE CENTRAL AND
NORTHERN BASINS. SHORTWAVE HIGH PRESSURE THEN BUILDS IN BRIEFLY
ON TUESDAY AS A STRONGER SHORTWAVE TROUGH MOVES FROM THE WEST
COAST INTO THE GREAT BASIN. THIS SYSTEM WHICH IS POISED TO
POTENTIALLY IMPACT THE AREA ON CHRISTMAS DAY, HAS A VARIABLE
TRACK AT THIS TIME. MODELS ARE TRENDING TOWARD A MORE SOUTHERLY
TRACK THROUGH UTAH AND COLORADO, WHICH WOULD LESSEN THE CHANCES
OF SNOW FOR MUCH OF WYOMING. WILL CERTAINLY NEED TO KEEP AN EYE
ON THE POSSIBILITIES AS WE HEAD INTO THE WEEKEND. THE ACTIVE
PATTERN IS EXPECTED TO CONTINUE FOR THE LATTER HALF OF NEXT
WEEK, THOUGH DETAILS ARE UNCERTAIN AT THIS TIME.
AVIATION /00Z TAFS THROUGH 00Z FRIDAY/
ISSUED AT 344 PM MST WED DEC 18 2024
A SHORTWAVE TROUGH PUSHES THROUGH TONIGHT, 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 6 HOURS OF THE PERIOD. GUSTS
OF 40 TO 45KTS WILL BE COMMON AT KCOD AND KCPR THROUGH THE 06Z. LLWS
AT KCOD UP TO 60 TO 65KTS IS ALSO POSSIBLE. THERE IS A 30% CHANCE
THAT DOWNVALLEY NORTHWESTERLY WINDS WILL PUSH INTO KRIW EARLY IN THE
PERIOD. SEVERAL MODELS, MOST NOTABLY THE HRWFV3 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. WINDS WILL SIGNIFICANTLY TAPER OFF TOWARDS SUNRISE
THURSDAY FOR ALL TERMINALS, WITH WINDS LESS THAN 12KTS EVERYWHERE BY
12Z.
THE OTHER NOTABLE AVIATION CONCERN WILL BE FOG. THIS WILL BE A
CONCERN FOR ALL WEST OF THE DIVIDE TERMINALS AFTER 01Z THROUGH THE
END OF THE PERIOD. 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...MCDONALD
AVIATION...HENSLEY
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