628
FXUS65 KRIW 291725
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1125 AM MDT THU MAY 29 2025
KEY MESSAGES
- WARMER AND DRIER TODAY AND FRIDAY, WITH ISOLATED SHOWERS AND
THUNDERSTORMS IN THE AFTERNOON.
- THE WARMEST WEATHER OF THE YEAR SO FAR 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 (80% 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 SUNRISE. 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 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 /18Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 1125 AM MDT THU MAY 29 2025
WITH THE UPPER-LEVEL RIDGE AXIS TO OUR WEST, A STATIONARY
BOUNDARY STILL STRETCHES FROM NW TO SE ACROSS WESTERN WY. AS A
WEAK DISTURBANCE MOVES INTO SW MT THIS AFTERNOON, THE RESIDUAL
MOISTURE AND SURFACE WIND CONVERGENCE IS EXPECTED TO BRING
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS TO AREAS OF THE
WESTERN MOUNTAINS AND SURROUNDING FOOTHILLS, ESPECIALLY TO THE
SOUTHEAST OF INITIATION. VFR CONDITIONS ARE GENERALLY EXPECTED
AT ALL TAF SITES, THOUGH KBPI/KPNA/KRKS/KCOD COULD SEE MVFR
CONDITIONS UNDER THE STORMS AS THE MOVE TO THE SOUTHEAST OFF THE
HIGHER TERRAIN. THE BEST TIMING FOR THE STORMS APPEARS TO BE
FROM 29/21Z TO 30/02Z. CLOUDINESS THIS MORNING HAS MOVED SOUTH
INTO CO, BUT SKIES SHOULD THICKEN THROUGH THE AFTERNOON HOURS
ACROSS THE WESTERN HALF OF THE STATE. THE CLOUDINESS WILL SLOWLY
MOVE EASTWARD OVERNIGHT WITH CLEARING IN FAR WESTERN WY FRIDAY
MORNING. THE TAF SITES IN SW WY SHOULD SEE GUSTY NORTHWEST WINDS
THIS AFTERNOON, AND CONVECTION WILL LIKELY INCREASE GUSTS TO
25-30 KTS WITH WEAK OUTFLOW.
AS THE BEFORE-MENTIONED DISTURBANCE MOVES INTO SE MT
FRIDAY MORNING, A SURFACE FRONT WILL PUSH SOUTHWARD EAST OF THE
DIVIDE FRIDAY MORNING, IMPACTING KCOD/KWRL/KBYG FIRST, THEN
MOVING INTO CENTRAL WY. CEILINGS WILL LIKELY LOWER TO 5-8K FEET
WITH VERY ISOLATED SHOWERS IN THE MORNING, AND ISOLATED SHOWERS
AND THUNDERSTORMS EAST OF THE DIVIDE FRIDAY AFTERNOON. FRIDAY
LATE MORNING AND AFTERNOON WILL THEN SEE GUSTY NORTH WINDS EAST
OF THE DIVIDE, WITH GUSTY NORTHWEST WIND ON THE WEST SIDE IN THE
AFTERNOON.
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...MCDONALD
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