812
FXUS65 KRIW 242245
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
345 PM MST WED DEC 24 2025
KEY MESSAGES
- MILD TEMPERATURES TODAY, WITH MORE RECORD HIGHS POSSIBLE.
- AN APPROACHING WEATHER SYSTEM BRINGS 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 SEASONABLE
TEMPERATURES LIKELY FOR THE WEEKEND AND INTO NEXT WEEK.
UPDATE
ISSUED AT 1220 PM MST WED DEC 24 2025
NO MAJOR CHANGES TO THE FORECAST FOR THE NEXT 24 HOURS OR SO.
EFI/SOT IS HIGHLIGHTING PORTIONS OF WESTERN YELLOWSTONE (PITCHSTONE
PLATEAU AND THE NORTHWEST CORNER) FOR SNOW, SO HAVE UPPED AMOUNTS
SLIGHTLY THERE, BUT CAUTION DOING TOO MUCH AS MODELS SEEM TO BE
OVERDOING SNOW WITH MANY SYSTEMS SO FAR THIS SEASON. ALSO
CONTINUED TO DROP PRECIPITATION CHANCES EAST OF THE DIVIDE AS
HIGH-RESOLUTION MODELS CORRECTLY HAVE PRECIPITATION STRUGGLING
TO MAKE IT OVER THE MOUNTAINS.
DISCUSSION
ISSUED AT 212 AM MST WED DEC 24 2025
TWAS THE SHIFT BEFORE CHRISTMAS, AND ALL 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 OF 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 AGAIN TODAY.
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
CELSIUS THROUGH MOST OF TONIGHT, IT 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 AN 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
CELSIUS PUT 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 PUT 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 ALONG AND BEHIND ITS 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 /00Z TAFS THROUGH 00Z FRIDAY/
ISSUED AT 345 PM MST WED DEC 24 2025
WEST OF THE CONTINENTAL DIVIDE...KJAC/KRKS/KPNA/KBPI TERMINALS
SHORTWAVE ENERGY EJECTS NORTHEAST AND CROSSES THE STATE TONIGHT
AHEAD OF A LONGWAVE TROUGH OFF THE US WEST COAST. THIS RESULTS IN
LIGHT RAIN BECOMING WIDESPREAD AT KJAC BETWEEN 03Z-06Z/THURSDAY.
TEMPERATURES REMAIN WARM ENOUGH TO KEEP LIGHT SNOW CONFINED TO THE
MOUNTAINS WITH VALLEY RAIN PERSISTING. MVFR CONDITIONS PREVAIL
OVERNIGHT AT KJAC, WHILE THE POTENTIAL FOR IFR LINGERS AROUND 30
PERCENT BETWEEN 10Z-15Z/THURSDAY. THE SHORTWAVE PROVIDES A PERIOD OF
LOWERED CEILINGS AND THE POTENTIAL FOR MVFR AT KBPI, KPNA, AND KRKS
BETWEEN 13Z-17Z/THURSDAY. CONDITIONS MOVE TO VFR AT ALL TERMINALS
THURSDAY AFTERNOON, ALTHOUGH A COLD POOL ALOFT LEADS TO INSTABILITY
SHOWERS IN THE VICINITY OF KJAC. GUSTY SOUTH TO SOUTHWEST WIND
WITHIN THE LOWEST 2K FEET AGL LEADS TO AN INCREASED LIKELIHOOD OF
LOW-LEVEL WIND SHEAR LATE TONIGHT AT KJAC, KBPI, AND KPNA. AS THE
SHORTWAVE SWEEPS EAST, THE LLWS POTENTIAL DIMINISHES BETWEEN 13Z-
17Z/THURSDAY. MOUNTAIN TOPS OBSCURED THROUGH 17Z/THURSDAY, WITH
FREQUENT MOUNTAIN TOP OBSCURATIONS TO FOLLOW.
EAST OF THE CONTINENTAL DIVIDE...KCPR/KCOD/KRIW/KLND/KWRL TERMINALS
MID/HIGH-LEVEL CLOUD COVER INCREASES ACROSS THE REGION TONIGHT AHEAD
OF A LONGWAVE TROUGH ALONG THE US WEST COAST. THE MAIN AVIATION
HAZARD REMAINS GUSTY SURFACE SOUTH TO SOUTHWEST WIND. GUSTS 25-40KTS
PERSIST AT KCPR THROUGH THE PERIOD, WHILE OTHER TERMINALS GENERALLY
SEE THE WIND INCREASE BY 04Z/THURSDAY AS SHORTWAVE ENERGY EJECTING
FROM THE LONGWAVE TROUGH TRACKS INTO THE STATE. DOWNSLOPING
SOUTHWEST WIND AT KLND LEADS TO LOW-LEVEL WIND SHEAR, ESPECIALLY
AFTER 06Z/THURSDAY UNTIL MIDDAY THURSDAY. SURFACE WIND SWINGS A BIT
MORE TO THE WEST AND GUSTS 20-35KTS THURSDAY AFTERNOON IN THE WAKE
OF SHORTWAVE PASSAGE. OTHER THAN SOME LOWERED MID-CLOUD DECKS,
CONDITIONS REMAIN VFR AT ALL TERMINALS THROUGH THE PERIOD. MOUNTAIN
TOPS OCCASIONALLY OBSCURED 03Z-18Z/THURSDAY.
PLEASE SEE THE AVIATION WEATHER CENTER AND/OR CWSU ZLC AND ZDV 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.
UPDATE...WITTMANN
DISCUSSION...HATTINGS
AVIATION...CNJ
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