379
FXUS65 KRIW 240922
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
222 AM MST WED DEC 24 2025
KEY MESSAGES
- ANOTHER MILD DAY TODAY WITH MORE RECORD HIGH TEMPERATURES
POSSIBLE.
- AN APPROACHING WEATHER SYSTEM WILL BRING MORE SNOW TO THE
WESTERN MOUNTAINS AND STRONG TO HIGH WIND FROM SOUTH PASS AND
MUDDY GAP THROUGH CASPER.
- ANOTHER WEATHER SYSTEM FOLLOWS ON FRIDAY, WITH A RETURN TO
MORE SEASONABLE TEMPERATURES LIKELY FOR THE WEEKEND AND INTO
NEXT WEEK.
DISCUSSION
ISSUED AT 212 AM MST WED DEC 24 2025
TWAS THE SHIFT BEFORE CHRISTMAS, THE THROUGH THE WEATHER STATION,
METEOROLOGISTS WERE LOOKING AT OBSERVATIONS FROM ACROSS THE NATION.
COMBINED WITH WEATHER MODELS, RADAR AND DATA FROM SATELLITE,
TRYING TO BRING FORECASTS FOR TRAVELERS THROUGH THE DAY AND NIGHT.
AND ON THE INSIDE OF THE HUMBLE RIVERTON WEATHER ABODE,
THERE WERE DIFFICULT FORECAST DECISIONS TO BE MADE AT IT SHOWED.
ANOTHER PACIFIC WEATHER SYSTEM WAS APPROACHING FROM THE WEST,
AND SOME THE POSSIBLE TRAVEL IMPACTS MADE THE FORECASTER STRESSED.
SNOW WAS LIKELY OVER SOME OF THE HIGHER MOUNTAIN PASSES,
AND STRONG WIND COULD SLOW TRAVEL TO SPEEDS AS SLOW AS MOLASSES.
AND HOPES OF A WHITE CHRISTMAS FOR MOST WOULD BE DASHED,
AS RECENT MILD TEMPERATURES ARE NOT EXPECTED TO CRASH.
NOW BACK TO YOUR REGULARLY SCHEDULED WEATHER DISCUSSION. THINGS ARE
LARGELY QUIET RIGHT NOW, AS THEY WERE MUCH OF YESTERDAY. THE MAIN
STORY TODAY CONTINUES TO BE THE ABNORMALLY WARM TEMPERATURES, AS
MUCH AS 30 DEGREES ABOVE NORMAL. CASPER HAD THEIR THIRD WARMEST
DECEMBER HIGH TEMPERATURE IN STATION HISTORY YESTERDAY. WE ARE NOW
UP TO 53 RECORD HIGHS THIS MONTH AT OUR 9 OFFICIAL CLIMATE SITES.
SEVEN OF OUR OFFICIAL SITES ARE HAVING THE WARMEST FIRST 24 DAYS OF
THE MONTH IN THEIR STATIONS HISTORY (INCLUDING LANDER, WHICH HAS
RECORDS DATING BACK 134 YEARS). RIVERTON IS MORE THAN 4 DEGREES
ABOVE THE SECOND WARMEST PERIOD. AND THE TWO STATIONS THAT AREN'T
(CASPER AND BUFFALO) ARE RANKED 2ND AND 3RD. AND WITH SOUTHWEST FLOW
CONTINUING TODAY, WE WILL LIKELY SEE MORE RECORD HIGH TEMPERATURES
THIS AFTERNOON. AS FOR PRECIPITATION, A FEW SHOWERS WILL DEVELOP
WEST OF THE DIVIDE, BUT NOTHING OF NOTE, AT LEAST UNTIL AROUND
SUNSET.
THINGS GET MORE ACTIVE TONIGHT. WE HAD TWO DECISIONS TO MAKE TONIGHT
IN REGARDS TO POTENTIAL HIGHLIGHTS, ONE FOR WIND AND ONE FOR SNOW.
WE WILL START WITH WIND. PART OF THE REASON IT HAS BEEN SO WARM IS
THE STRONG SOUTHWEST WIND, WHICH HAS BEEN AT TIMES VERY STRONG. WE
WILL HAVE A DECENT SETUP FOR STRONG WIND. THE PRESSURE GRADIENT WILL
TIGHTEN AHEAD OF AN ADVANCING PACIFIC COLD FRONT AND TROUGH. THE 700
MILLIBAR WINDS ARE EXPECTED TO INCREASE TO 50 TO 60 KNOTS AHEAD OF
THE SYSTEM. WE WILL ALSO HAVE THE RIGHT FRONT QUADRANT OF AN 100
KNOT JET STREAK PROVIDING SOME DOWNWARD FORCING. IN THE REALM OF
PROBABILISTIC GUIDANCE, AREAS FROM MUDDY GAP THROUGH CASPER LOOK TO
HAVE AT LEAST A 2 IN 3 CHANCE OF EXCEEDING GUSTS OF 55 MPH. SO, WE
WENT AHEAD AND UPGRADED THE WATCH TO A WARNING AND ADDED A COUPLE OF
ZONES. WE ADDED CASPER MOUNTAIN FOR ONE, WITH AT LEAST A 1 IN 2
CHANCE OF GUSTS PAST 65 MPH. THE OTHER ZONE WAS A BIT OF A TOUGHER
DECISION.
THIS IS THE EASTERN SLOPES OF THE WIND RIVER MOUNTAINS. WE THOUGHT
ABOUT A WINTER WEATHER ADVISORY INSTEAD. HOWEVER, SOUTHWEST FLOW IS
MORE CONDUCIVE TO WESTERN PORTIONS OF THE RANGE. WE ALSO THOUGHT
ABOUT IMPACTS. THE MAIN ROAD IN THIS AREA, SOUTH PASS, ONLY HAS
AROUND A 1 IN 4 CHANCE OF 2 INCHES OF SNOW OR MORE. AND WITH 700
MILLIBAR TEMPERATURES EXPECTED TO REMAIN ABOVE ZERO THROUGH MOST OF
TONIGHT, TO WOULD BE MAINLY RAIN FOR PRECIPITATION. WITH THE BUSY
HOLIDAY TRAVEL DAY, WE FELT THE MAIN IMPACT WOULD BE HIGH WIND. SO,
WE WENT WITH HIGH WIND. THERE COULD BE SOME BLOWING SNOW PROBLEMS AS
WELL THOUGH, ESPECIALLY CHRISTMAS MORNING AS SOMEWHAT COOLER AIR
MOVES IN. THERE WILL LIKELY BE SOME ADVISORY AMOUNTS OF SNOW IN THE
HIGHER ELEVATIONS, BUT IMPACTS THERE THIS TIME OF YEAR WOULD BE
RATHER LIMITED.
NOW FOR THE SNOWY SIDE OF THE SYSTEM. STEADIER PRECIPITATION WILL
MOVE IN THIS EVENING AS THE FRONT AND BETTER UPPER LEVEL FORCING
APPROACH THE AREA. THE 700 MILLIBAR TEMPERATURES SHOULD REMAIN ABOVE
ZERO CELSIUS THROUGH AROUND 8 PM TONIGHT, WHEN THE ARRIVAL OF THE
FRONT BEGINS TO LOWER THE LEVELS. THE REAL DROP DOESN'T COME UNTIL
AROUND SUNRISE CHRISTMAS MORNING THOUGH, WHEN THEY FALL TO AROUND
MINUS 3 CELSIUS, PUTTING SNOW LEVELS AROUND 7000 FEET. THIS SHOULD
KEEP SNOW LEVELS ABOVE THE VALLEY LOCATIONS, EXCEPT POSSIBLY TOWARD
THE END OF THE EVENT WHEN THERE COULD BE A SMALL ACCUMULATION. THE
MAIN IMPACTS WOULD BE THE PASSES, ESPECIALLY TOGWOTEE PASS WITH ITS
ALMOST 10000 FOOT ELEVATION. HERE, AS WELL AS TETON PASS, WITH AT
LEAST A 1 IN 2 CHANCE OF 6 INCHES OR MORE OF SNOW, WE HAVE HOISTED
WINTER WEATHER ADVISORIES. AND, GIVEN THE FAVORABLE UPSLOPE
FLOW, ADDED ON FOR THE WESTERN WIND RIVER RANGE AS WELL. IF
THIS WAS A RANDOM DAY, WE MAY HAVE HELD OFF. HOWEVER, GIVEN THE
HOLIDAY TRAVEL CONCERNS, ALONG WITH SOME GUSTY WIND BRINGING
BLOWING SNOW, WE WENT AHEAD AND ISSUED. THE HEAVIEST SNOW WOULD
FALL BETWEEN MIDNIGHT AND NOON ON CHRISTMAS DAY, WHEN THE TROUGH
AXIS PASSES AND THE BEST JET DYNAMICS MOVE THROUGH. AND
FINALLY, SOME MODELS ARE INDICATING NEGATIVE LIFTED INDICES IN
WESTERN WYOMING, SO WE CAN'T RULE OUT A STRAY THUNDERSTORM
CHRISTMAS AFTERNOON.
OTHERWISE, CHRISTMAS DAY LOOKS TO BE ANOTHER WELL ABOVE NORMAL
DAY TEMPERATURE WISE, WITH MORE RECORD HIGHS POSSIBLE. THERE
COULD BE A FEW SHOWERS, BUT THE DOWNSLOPING FLOW SHOULD KEEP
MOST AREAS EAST OF THE DIVIDE MAINLY DRY. WIND SHOULD DECREASE
SOMEWHAT IN THE AFTERNOON AS THE SYSTEM MOVES AWAY. AND AS A
RESULT, THE CHANCE OF A WHITE CHRISTMAS IS BASICALLY ZERO.
ANOTHER SYSTEM WILL BE ON THIS ONE'S HEELS FOR FRIDAY. THIS ONE HAS
SOMEWHAT COOLER AIR WITH IT AND SHOULD PUT AND END TO THE RECORD
HIGHS FOR MOST LOCATIONS. BUT NOT DURING THE DAY ON FRIDAY, WHEN WE
MAY HAVE ONE MORE DAY OF RECORD HIGHS. AS FOR THE NEXT SYSTEM, THIS
ONE HAS MORE JET FORCING WITH IT AND AS A RESULT PRECIPITATION LOOKS
TO BE MORE OF THE BANDED VARIETY AND HARD TO PINPOINT. WITH THE
COOLER AIR WITH THIS SYSTEM (COOLER, BUT NOT COLD, ESPECIALLY BY
WYOMING STANDARDS), THERE COULD BE SOME SNOW IN THE VALLEYS AS 700
MILLIBAR TEMPERATURES OF MINUS 5 BUT SNOW LEVELS AT 6000 FEET. AND
EAST OF THE DIVIDE, THERE COULD BE STRONG WIND AGAIN, ALTHOUGH HIGH
WIND IS MORE QUESTIONABLE.
WE WILL FINALLY BUT AN END TO THE WARM WEATHER ON SATURDAY NIGHT AND
SUNDAY , AS A COLD FRONT DROPS OUT OF MONTANA AND BRINGS SOME MORE
TYPICAL DECEMBER WEATHER. HOWEVER, THE AIR IS NOT TERRIBLY COLD AND
WITH THE LACK OF SNOW COVER, TEMPERATURES WILL ONLY FALL BACK TO
NEAR NORMAL LEVELS. THE FRONT COULD ALSO BRING SOME SNOW SHOWERS
WITH AND BEHIND IT'S PASSAGE. HOWEVER, MOISTURE IS LIMITED SO ANY
ACCUMULATIONS LOOK MINOR. HIGH PRESSURE SHOULD THEN BRING DRY AND
MORE SEASONABLE WEATHER FOR EARLY NEXT WEEK AND POSSIBLY INTO
THE START OF 2026.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 930 PM MST TUE DEC 23 2025
VFR CONDITIONS EXPECTED THROUGHOUT THE PERIOD FOR ALL LOCATIONS.
WINDS HAVE DIMINISHED TO 10KTS OR LESS FOR THE OVERNIGHT HOURS
EXCEPT FOR REMAINING ELEVATED AT CPR WITH A 18KT BREEZE.
INCREASING UPPER LEVEL CLOUDS INTO WEDNESDAY AHEAD OF THE NEXT
SYSTEM LOWERING TO THE MID LEVELS WEST TO EAST 20-00Z. LIGHT
RAIN EXPECTED AT JAC BY 20Z PUSHING TO BPI/PNA BY 02Z BUT WITH
LESS CONFIDENCE CARRYING VCSH. RESTRICTED VISIBILITY AND LOWER
CEILINGS POSSIBLE TO MVFR AT JAC AFTER 02Z CARRYING A TEMPO
THROUGH THE END OF THE PERIOD WITH A 20-30% CONFIDENCE LEVEL
IAW MUCH OF THE HI-RES DATA. OTHERWISE, WINDS INCREASE WITH THE
SYSTEM AFTER 00Z GUSTING UP TO 25KTS EAST OF THE DIVIDE ALONG
WITH RKS, HIGHEST AT CPR DURING THE AFTERNOON UP TO 35KTS. THESE
WILL REMAIN ELEVATED INTO THE OVERNIGHT HOURS INTO CHRISTMAS
MORNING AS WELL.
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
WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 5 PM MST
THURSDAY FOR WYZ012-014.
HIGH WIND WARNING FROM 7 PM THIS EVENING TO 11 AM MST THURSDAY
FOR WYZ015-019-020-022.
DISCUSSION...LAVOIE
AVIATION...LOWE
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