372
FXUS65 KRIW 271929
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1229 PM MST SAT DEC 27 2025
KEY MESSAGES
- A POTENT COLD FRONT HAS BEGUN TO MOVE ACROSS NORTHERN WY,
BRINGING WITH IT SHARPLY DROPPING TEMPERATURES, GUSTY WINDS,
AND CHANCES FOR SNOW SHOWERS.
- SOME OF THE COLDEST TEMPERATURES SETTLE OVER THE REGION FOR
SUNDAY AND MONDAY.
- QUIET AND MILD WEATHER RETURNS TO THE COWBOY STATE FOR THE END
OF THE YEAR WITH THE NEXT CHANCE FOR UNSETTLED WEATHER NOT
ARRIVING UNTIL THE END OF THE NEXT WEEK.
UPDATE
ISSUED AT 1205 PM MST SAT DEC 27 2025
THE POTENT COLD FRONT MENTIONED IN THE PREVIOUS DISCUSSION IS
CURRENTLY MAKING ITS WAY INTO PORTIONS OF NORTHERN WY. WINDS ARE
STARTING TO INCREASE ACROSS THE AREA WITH PERIODIC GUSTS OF 30
TO 40 MPH WITH STRONGER GUSTS AROUND 50 MPH NEARBY BUFFALO.
TEMPERATURES ARE QUICKLY DROPPING BEHIND THE FRONT WITH SOME
LOCATIONS SEEING A 10 TO 20 DEGREE DIFFERENCE IN LESS THAN 30
MINUTES. SNOW SHOWERS WILL FOLLOW BEHIND THE FRONTAL PASSAGE
WITH SOME LOCATIONS IN THE NORTHERN BIGHORN BASIN ALREADY SEEING
SNOWFALL. SOME MODERATE TO HEAVY BANDS OF SNOW ARE POSSIBLE THIS
AFTERNOON AND EVENING. THE BEST CHANCES FOR THESE BANDS LOOK TO
BE ACROSS PORTIONS OF THE BIGHORN BASIN AS WELL AS JOHNSON AND
NATRONA COUNTIES. HI-RES MODELS HAVE CONTINUED TO LESSEN THE
CHANCES FOR SHOWERS ACROSS PARTS OF CENTRAL WY THIS EVENING INTO
THE EARLY MORNING HOURS ON SUNDAY. THIS IS DUE TO FAVORABLE
UPSLOPE FLOW NOT DEVELOPING, AS A RESULT CHANCES FOR SNOW OVER
PARTS OF THE WIND RIVER BASIN AND LANDER FOOTHILLS HAS
SIGNIFICANTLY DECREASED. AN ISOLATED SHOWER CANNOT BE RULED OUT
FOR THIS AREA BUT THE MORE FAVORABLE LOCATIONS LOOK TO BE EAST
INTO NATRONA COUNTY.
TEMPERATURES THAT FOLLOW BEHIND THE FRONT WILL BE SOME OF THE
COLDEST SO FAR THIS MONTH. LOWS SUNDAY MORNING RANGE FROM THE
SINGLE DIGITS TO BELOW ZERO OVER PORTIONS OF WESTERN AND
NORTHERN WY. CENTRAL BASINS AND SOUTHERN WY LOOK TO BE SLIGHTLY
WARMER WITH LOWS IN THE UPPER SINGLE DIGITS TO LOW TEENS. ONE
AREA TO MONITOR WOULD BE PORTIONS OF JOHNSON COUNTY AND PARTS OF
THE BIGHORN BASIN. IF SOME SNOW ACCUMULATION IS ABLE TO OCCUR
AND SKIES CAN CLEAR OUT QUICKLY ENOUGH DURING THE MORNING
SUNDAY. IT IS NOT OUT OF THE REALM OF POSSIBILITY FOR SOME
LOCATIONS TO SEE LOW TEMPERATURES BELOW ZERO. OTHERWISE, THE
FORECAST REMAINS MOSTLY UNCHANGED WITH MILD TEMPERATURES AND
MAINLY QUIET WEATHER RETURNING BY THE END OF THE YEAR.
DISCUSSION
ISSUED AT 304 AM MST SAT DEC 27 2025
MUCH OF WYOMING IS ABOUT TO GET A DOSE OF WHAT WINTER IN
WYOMING USUALLY IS. IF YOU DON'T LIKE COLD WEATHER, IT HAS BEEN
A CHARMED LIFE OVER THE PAST 2 WEEKS, WITH MOST LOCATIONS 15 TO
AS MUCH AS 22 DEGREES ABOVE NORMAL. WE STARTED COOLING
YESTERDAY, AND THAT WILL CONTINUE TODAY. BUT THE SLAP WILL
REALLY HIT TONIGHT AND INTO THE SUNDAY AND MONDAY.
WE DO HAVE SOME SNOW FALLING LARGELY ACROSS THE WESTERN MOUNTAINS.
THERE IS ALSO SOME ACROSS EASTERN SWEETWATER COUNTY. THE LAST ROUND
OF PRECIPITATION WILL OCCUR WITH THE ARRIVAL OF THE NEXT SYSTEM, A
CANADIAN COLD FRONT THAT WILL DROP ACROSS THE AREA TODAY AND
TONIGHT. THIS FRONT WILL HAVE THREE THINGS TO TALK ABOUT: SNOW, WIND
AND COLDER TEMPERATURES.
AS FOR SNOW, THERE SHOULD NOT BE A LOT OF IT. AS WITH MOST CANADIAN
OR ARCTIC FRONTS, THERE IS LITTLE MOISTURE WITH IT. AS WE LOOK INTO
THE PROBABILISTIC REALM OF ENSEMBLES, THE ONLY ARE WITH A GREATER
THAN 1 IN 2 CHANCE OF 6 INCHES OR MORE OF SNOW STARTING AT 5 AM IS
THE TETONS, WITH MOST LOCATIONS HAVING LESS THAN 1 IN 10 CHANCE. THE
CHANCE OF 3 INCHES IS HIGHER BUT AGAIN, ONLY IN THE MOUNTAINS FOR
THE MOST PART. WE DO HAVE WINTER WEATHER ADVISORIES AND WE WILL
LEAVE THESE UP, MAINLY FOR TRAVEL OVER THE PASSES. AS FOR THE LOWER
ELEVATIONS, OTHER THAN THE WESTERN VALLEYS, THE CHANCE OF 2 INCHES
OR MORE OF SNOW IS AT MOST 1 OUT 4, AND THAT IS THE PLACES LIKE
SINKS CANYON AND SOUTH OF WYOMING BOULEVARD WHERE THERE COULD BE A
BRIEF PERIOD OF UPSLOPE ENHANCEMENT. CHANCES OF AN INCH OR SNOW DO
INCREASE TO AS HIGH AS 3 OUT OF 5 THROUGH IN A CRESCENT FROM JOHNSON
COUNTY TO CASPER TO THE WIND RIVER BASIN TO THE CODY FOOTHILLS. THIS
SNOW WILL BE OF THE ANAFRONTAL VARIETY, OCCURRING BEHIND THE FRONT.
THE BEST CHANCE WOULD BE FROM THE AFTERNOON INTO THE NIGHT TIME
HOURS. THE SYSTEM IS A FAST MOVING ONE THOUGH, WITH ALL SNOW LIKELY
DONE BY SUNRISE SUNDAY. WITH THE LIGHT AMOUNTS OF SNOW, NO FURTHER
HIGHLIGHTS WILL BE ISSUED AT THIS TIME.
NOW WE MOVE ON TO WIND. THERE WILL BE A GUSTY WEST TO SOUTHWEST WIND
AHEAD OF THE FRONT, BUT WITH 700 MILLIBAR GENERALLY REMAINING BELOW
50 KNOTS, ANY HIGH WIND GUST WOULD BE ISOLATED. IT COULD WARM THINGS
UP A BIT, AND IT IS NOT OUT OF THE QUESTION THAT A PLACE LIKE
RIVERTON, WHICH HAS LOW RECORD HIGHS, COULD SET ANOTHER ONE TODAY.
THE CONCERN FOR WIND THEN SHIFTS THE NORTHWEST FLOW / COLD ADVECTION
LOCATIONS POST FRONTAL, FIRST IN PLACES LIKE BUFFALO AND GREYBULL IN
THE AFTERNOON. THEN INTO CENTRAL WYOMING AFTER SUNSET. LIKE PRE
FRONTAL, MID LEVEL WIND DOES NOT SUPPORT HIGH WIND. HOWEVER,
PROBABILISTIC GUIDANCE DOES SHOW AROUND A 1 IN 2 CHANCE OF WIND
GUSTS PAST 50 MPH IN THE FAVORED AREAS AFTER THE FRONTAL PASSAGE.
THIS WOULD BE A BRIEF PERIOD OF STRONGER WIND, GENERALLY LESS THAN 6
HOURS. WE WILL NOT ISSUE ANY WIND HIGHLIGHTS FOR NOW, BUT MAY
ISSUE A SPECIAL WEATHER STATEMENT, ESPECIALLY FOR JOHNSON COUNTY
WHERE THE WIND MAY BE THE STRONGEST WITH A BETTER CHANCE OF SOME
ACCUMULATING SNOW.
AND NOW ON TO TEMPERATURES. THERE IS A NAME FOR THE TEMPERATURES
THAT WILL BE FOUND BEHIND THE FRONT, SEASONABLE. LOWS SUNDAY AND
MONDAY NIGHT WILL BE FAIRLY CLOSE OR SOMEWHAT BELOW SEASONAL
AVERAGES, BUT FAIRLY TYPICAL FOR THE LAST DAYS OF DECEMBER. IT WILL
FEEL QUITE COLD THOUGH, THAT SLAP IN THE FACE COMPARED TO MILD
WEATHER WE HAVE HAD OVER THE PAST COUPLE OF WEEKS. SOME PORTIONS OF
NORTHERN WYOMING WILL HAVE AROUND A 1 IN 3 CHANCE OF LOW
TEMPERATURES BELOW ZERO, ESPECIALLY AREAS THAT GET SOME SNOW THIS
AFTERNOON AND EVENING. IT WILL FEEL BELOW ZERO THOUGH WITH THE GUSTY
WIND, BUT NOT COLD ENOUGH FOR WIND HIGHLIGHTS. AND THERE IS ANOTHER
CONCERN. WITH THE RECENT WARM TEMPERATURES, THE GROUND IS FAIRLY
WARM. THIS IS A FAIRLY GOOD SETUP FOR A FLASH FREEZE WITH THE SNOW
INITIALLY MELTING ON ROADS AND RAPIDLY FALLING TEMPERATURES BEHIND
THE FRONT.
COLD TEMPERATURES WILL STICK AROUND INTO SUNDAY AND SUNDAY NIGHT.
BUT FOR THOSE PEOPLE WHO DON'T LIKE COLD WEATHER, THERE IS GOOD
NEWS. NORTHERLY FLOW WILL START TO TURN MORE ZONAL AND BRING IN
MILDER AIR FROM THE PACIFIC. AND, ONCE AGAIN, LEAD TO ANOTHER PERIOD
OF ABOVE NORMAL TEMPERATURES. IT WILL NOT BE AS WARM AS BEFORE
CHRISTMAS, BUT TEMPERATURES 10 TO 15 DEGREES ABOVE NORMAL MAY APPEAR
AS EARLY AS TUESDAY AND ALMOST CERTAINLY BY WEDNESDAY INTO THE REST
OF THE WEEK. THIS ALSO LOOKS LIKE A DRY PATTERN. THE NEXT CHANCE OF
PRECIPITATION WOULD NOT ARRIVE UNTIL THE END OF THE WEEK IN THE FORM
OF A PACIFIC TROUGH, BUT DETAILS THIS FAR OUT ARE STILL DIFFICULT TO
NAIL DOWN.
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1046 AM MST SAT DEC 27 2025
WEST OF THE CONTINENTAL DIVIDE...KJAC/KRKS/KPNA/KBPI TERMINALS
WEST-SOUTHWEST FLOW ALOFT CONTINUES TO SPREAD LIGHT SNOW ACROSS KJAC
LATE SUNDAY MORNING AHEAD OF AN UPSTREAM SHORTWAVE DROPPING SOUTH
SUNDAY AFTERNOON. IFR/MVFR SNOW PERSISTS THROUGH MUCH OF SUNDAY
EVENING, WITH A POTENTIAL PERIOD OF LIFR CONDITIONS 19Z-23Z.
THERE COULD BE OCCASIONAL BRIEF PERIODS OF IMPROVED CONDITIONS
AFTER 02Z/SUNDAY. FLURRIES MAY CONTINUE OVERNIGHT AT KJAC AND
THERE IS A THREAT OF BKN025 CEILING PERSISTING INSTEAD OF RISING
TO LOW-END VFR. FOR NOW, HAVE LIFTED CEILINGS AFTER 10Z/SUNDAY
AT KJAC. OTHER TERMINALS GENERALLY SEE BKN040-080 CEILINGS WITH
INCREASING WESTERLY WIND BY EARLY SUNDAY AFTERNOON. THESE WINDS,
WHILE SOME DROP-OFF IN SPEEDS IS EXPECTED, PREVAIL OVERNIGHT AS
THE AFOREMENTIONED SHORTWAVE SWEEPS ACROSS THE REGION. CLOUD
COVER CLEARS LATE TONIGHT LEAVING VFR FOR SUNDAY. GUSTY WEST-
NORTHWEST WIND INCREASES AT KRKS, KPNA, AND KBPI AROUND MIDDAY
SUNDAY. MOUNTAINS OBSCURED THROUGH 06Z/SUNDAY, WITH MOUNTAIN
TOPS OBSCURED THROUGH 12Z/SUNDAY.
EAST OF THE CONTINENTAL DIVIDE...KCPR/KCOD/KRIW/KLND/KWRL TERMINALS
A VIGOROUS SURFACE COLD FRONT JUST REACHED KPOY AT 17Z/SATURDAY, AND
IS POISED TO REACH KCOD BY THE START OF THE FORECAST PERIOD. GUSTY
WEST-SOUTHWEST WIND AHEAD OF THE FRONT WILL ABRUPTLY SWITCH TO THE
NORTH TO NORTHWEST BEHIND THE FRONT. THE INITIAL SURGE COULD SEE 25-
35KT GUSTS AS IT MOVES TO KWRL BY 20Z/SATURDAY AND A KLND-KCPR LINE
AROUND 00Z-01Z/SUNDAY. THE FRONTAL PASSAGE FAVORS NORTHERLY
UPSLOPE FLOW AND ASSOCIATED MID-LEVEL INSTABILITY GENERATES
LIGHT SNOW TONIGHT AT KCPR. THIS RESULTS IN A PERIOD OF EVENING
MVFR SNOW AT KCPR BEFORE IFR SNOW ARRIVES FOR THE 04Z-10Z/SUNDAY
PERIOD. THE ENSEMBLES ARE LESS ENTHUSIASTIC ABOUT LIGHT SNOW AT
KRIW AND KLND BETWEEN ABOUT 04Z-08Z/SUNDAY. FAVORABLE UPSLOPE
FLOW LOOKS LESS LIKELY AS SURFACE WINDS MAY NOT MOVE AROUND TO
THE NORTH- NORTHEAST, BUT RATHER STAY NORTH- NORTHWEST OR
NORTHWEST. THEREFORE, HAVE TRENDED BACK CHANCES AT THESE TWO
TERMINALS. A SHORTWAVE TROUGH CLEARS THE REGION BETWEEN 12Z-
15Z/SUNDAY ALLOWING FOR VFR TO RETURN TO ALL TERMINALS. MOUNTAIN
TOPS OBSCURED 19Z/SATURDAY TO 10Z/SUNDAY.
PLEASE SEE THE AVIATION WEATHER CENTER AND/OR CWSU ZLC AND ZDV FOR
THE LATEST INFORMATION ON ICING AND TURBULENCE FORECASTS.
CLIMATE
ISSUED AT 304 AM MST SAT DEC 27 2025
ALTHOUGH IT WAS NOT AS WARM AS ON CHRISTMAS DAY, IT WAS STILL
WARM ENOUGH FOR 4 MORE RECORD HIGH TEMPERATURES, PUTTING THE
MONTHLY TOTAL UP TO 70, WITH 69 OCCURRING IN THE PAST TWO
WEEKS. THROUGH DECEMBER 26TH, ALL 9 MAJOR CLIMATE SITES EXCEPT
BUFFALO ARE AT LEAST 10 DEGREES FAHRENHEIT ABOVE NORMAL SO FAR
THE MONTH, WITH THE MOST ANOMALOUS BEING THE RIVERTON AIRPORT
WHICH IS 17.7 DEGREES FAHRENHEIT ABOVE NORMAL FOR THE MONTH.
RIW WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR
WYZ001-002-012-014-024.
UPDATE...DZIEWALTOWSKI
DISCUSSION...HATTINGS
AVIATION...CNJ
CLIMATE...HATTINGS
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