957
FXUS65 KRIW 290757
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
157 AM MDT THU MAY 29 2025
KEY MESSAGES
- WARMER AND DRIER TODAY AND FRIDAY WITH AN ISOLATED SHOWERS AND
THUNDERSTORMS.
- THE WARMEST WEATHER OF THE YEAR IS EXPECTED THIS WEEKEND, WITH
THE FIRST 90 DEGREE HIGH TEMPERATURES POSSIBLE SUNDAY.
- A TRANSITION TO A COOLER AND WETTER PATTERN IS LIKELY EARLY
NEXT WEEK (3 OUT OF 5 CHANCE).
DISCUSSION
ISSUED AT 156 AM MDT THU MAY 29 2025
THERE ARE STILL A FEW LEFTOVER SHOWERS OUT THERE EARLY THIS MORNING.
HOWEVER, RADAR TRENDS ARE DOWN AND WITH CLOUD TOPS CONTINUING TO
WARM, THESE SHOULD BE GONE BY SUNSET. CONVECTION SHOULD BE LESS
TODAY AS RIDGING BUILDS INTO THE AREA TODAY. ANY CONDITIONS WOULD BE
LIMITED TO IN AND NEAR THE MOUNTAINS, WITH AN EMPHASIS ON AREAS
ALONG AND WEST OF THE CONTINENTAL DIVIDE. THE CHANCE IS AT MOST 1 IN
3 IN MOST MOUNTAIN LOCATIONS, DROPPING TO AROUND 1 IN 4 TO 1 OUT OF
5 IN THE ADJACENT LOWER ELEVATIONS. WITH MORE SUNSHINE EXPECTED,
TEMPERATURES WILL BE WARMER, RISING TO NEAR TO SLIGHTLY ABOVE NORMAL
LEVELS FOR MOST LOCATIONS. LIKE TONIGHT, A VAST MAJORITY OF THESE
SHOWERS SHOULD BE OVER BY MIDNIGHT.
THERE IS MORE UNCERTAINTY FOR TOMORROW, MAINLY IN EASTERN PORTIONS
OF THE AREA. AND THE CULPRIT THAT IS CAUSING THE FIRST CONUNDRUM IN
THE IS A TROUGH / WEAK UPPER LEVEL LOW THAT WILL BE MOVING SOUTHWARD
OUT OF THE PRAIRIE PROVINCES IN CANADA. GUIDANCE IS SPLIT ON THE
POSITION OF THIS FEATURE, WITH THE GFS HAVING THE SYSTEM FURTHER
WEST, FAR ENOUGH TO WEST TO BRING SOME CONVECTION TO AREAS EAST OF
THE DIVIDE. OTHER GUIDANCE KEEPS THE LOW FURTHER EAST AND THE AREA
LARGELY DRY. FOR NOW, WE COMPROMISED AND WENT WITH LOW END POPS
(ABOUT 1 OUT OF 5) FOR MUCH OF THE AREA EAST OF THE DIVIDE. THE
OTHER CONCERN IS THE SYSTEM MAY TIGHTEN THE PRESSURE GRADIENT A BIT
AND BRING SOME GUSTY WIND, MAINLY IN AREAS FAVORED BY NORTHWEST FLOW
(JOHNSON COUNTY, NORTHERN BIG HORN BASIN) BUT HIGH WIND IS NOT
EXPECTED. THIS SYSTEM COULD ALSO KEEP TEMPERATURES COOLER IN JOHNSON
AND NATRONA COUNTY IF IT IS FURTHER WEST. WITH THE UNCERTAINTY WE
LEFT CONTINUITY ALONE. BUT EVEN IF THE WESTERN SOLUTION VERIFIES,
MOST AREAS WILL BE RAIN FREE MOST OF THE TIME.
RIDGING THEN REALLY AMPLIFIES FOR THE WEEKEND. SATURDAY LOOKS LIKE A
DRY DAY WITH TEMPERATURES AVERAGING 5 TO 10 DEGREES ABOVE NORMAL.
THE HEAT WILL PEAK ON SUNDAY AS SOUTHWEST FLOW INCREASES AHEAD OF A
PAIR OF UPPER LEVEL LOWS, ONE APPROACHING FROM THE SOUTHWEST AND ONE
FROM THE NORTHWEST. THIS COULD BE THE DAY WE SEE OUR FIRST 90 DEGREE
HIGHS OF THE YEAR, ESPECIALLY IN THE WARMER LOCATIONS LIKE GREYBULL
AND WORLAND. AND, WITH THE FEW DAYS OF WARMER WEATHER, WE HAVE SOME
FLOODING CONCERNS. WE STILL HAVE A DECENT AMOUNT OF SNOW ABOVE 9500
FEET AND THE WARM TEMPERATURES THIS WEEKEND COULD MELT THIS OUT AND
RAISE LEVELS ON CREEKS AND STREAMS. THE CHANCE OF CONVECTION WILL
ALSO RETURN, WITH SHOWERS AND THUNDERSTORMS POSSIBLE ACROSS THE
NORTHERN PORTIONS OF THE AREA.
AS WE HEAD INTO THE NEXT WEEK, WE HAVE SOME THINGS WE ARE FAIRLY
CONFIDENT IN A COOLER AND WETTER PATTERN AS WE COME UNDER THE
INFLUENCE OF THE TWO UPPER LEVEL LOWS. WE STILL HAVE VERY LOW
CONFIDENCE IN DETAILS OF THE PLACEMENT AND AMOUNTS OF POTENTIAL
PRECIPITATION. UPPER LEVEL LOWS ARE VERY FICKLE IN MOVEMENT AND THE
FACT WE HAVE TWO OF THEM MAKES IT EXPONENTIALLY HARDER TO PREDICT.
THIS COULD BE A RATHER WET PERIOD THOUGH. NBM ENSEMBLE GUIDANCE
SHOWS AT LEAST A 1 IN 2 CHANCE OF ALL LOCATIONS FOR A HALF AN INCH
OF RAIN FROM MONDAY MORNING THROUGH WEDNESDAY NIGHT WITH THE
NORTHERN HALF OF THE AREA HAVING A 1 OUT OF 2 CHANCE OF AN INCH OR
MORE THROUGH THE SAME TIME PERIOD. IN ADDITION, THE MOUNTAINS MAY
HAVE THE CHANCE FOR SOME SNOW. THE 700 MILLIBAR TEMPERATURES MAY
FALL AS LOW AS MINUS 1 ON MONDAY NIGHT OVER THE BIGHORNS WHICH COULD
LOWER SNOW LEVELS AS LOW AS 8000 TO 8500 FEET.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1000 PM MDT WED MAY 28 2025
SHOWERS CONTINUE TO WANE ACROSS THE AREA THIS EVENING AND ARE
EXPECTED TO AROUND AROUND THE START OF THE TAF PERIOD. WITH
LIGHT WINDS AND AMPLE LOW- LEVEL MOISTURE, FOG WILL BE A
POSSIBILITY THROUGH 15Z. MOST LIKELY CHANCES (30 TO 40%) ARE AT
KCPR, WITH LOW-LEVEL EASTERLY WINDS FILTERING MOISTURE AND LOW
CLOUDS IN FROM EASTERN WY AND INTO THE CASPER AREA. MODEL
GUIDANCE INDICATES THAT ANY FOG/LOW CLOUD IMPACTS SHOULD ONLY
LAST A FEW HOURS. HAVE CONTINUED WITH THE FEW005 GROUP TO HEDGE
TOWARDS THE FOG CHANCES, AS THERE IS NOT ENOUGH CONFIDENCE TO
INCLUDE A PREVAILING IFR OR MVFR GROUP.
PARTLY CLOUDY SKIES WILL BE IN PLACE ACROSS AREAS WEST OF THE
DIVIDE IN THE MORNING AND MOSTLY CLEAR ELSEWHERE. CLOUDS WILL
INCREASE OVER THE WESTERN MOUNTAINS AFTER 19Z, WITH SHOWERS AND
THUNDERSTORMS BECOMING OVER THE ABSAROKA AND WIND RIVER
MOUNTAINS, AS WELL AS YELLOWSTONE NP LATE IN THE AFTERNOON.
ISOLATED SHOWERS AND THUNDERSTORMS WILL ALSO BE POSSIBLE OVER
THE GREEN RIVER BASIN. KCOD, KPNA AND KRKS LOOK TO HAVE THE
MOST LIKELY CHANCES FOR SHOWERS OR THUNDERSTORMS (15 TO 20%
CHANCES), BUT NOT ENOUGH CONFIDENCE TO INCLUDE MENTIONS IN THE
TAFS AT THIS TIME. THIS CONVECTION WILL WANE THROUGH THE EVENING
HOURS ONCE AGAIN AND END BY THE END OF THE TAF PERIOD.
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
NONE.
DISCUSSION...HATTINGS
AVIATION...LAVOIE/HENSLEY
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