922
FXUS65 KRIW 292227
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
427 PM 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).
UPDATE
ISSUED AT 1241 PM MDT THU MAY 29 2025
NO REAL CHANGES IN THE FORECAST FOR TODAY OTHER THAN INCORPORATING
THE LATEST HIGH-RESOLUTION MODEL DATA FOR SHOWER/THUNDERSTORM
CHANCES; THERE IS A 15% TO 40% CHANCE OF A SHOWER OR STORM
ALONG AND WEST OF THE CONTINENTAL DIVIDE THROUGH THIS EVENING,
MAINLY OVER THE MOUNTAINS. A FEW SHOWERS COULD MOVE OFF THE
MOUNTAINS, INTO THE ADJACENT FOOTHILLS/LOWER ELEVATIONS.
THE REST OF THE WEEK IS LEFT MOSTLY THE SAME AS WELL. HAVE LOWERED
COVERAGE OF STORMS FOR TOMORROW. THERE COULD STILL BE A COUPLE POP-
UP STORMS DURING THE AFTERNOON FOR LOCATIONS ALONG AND EAST OF THE
DIVIDE, BUT WIDESPREAD CHANCES LOOK LOW. HOTTEST DAY CONTINUES TO
LOOK LIKE SUNDAY, WITH MOST AREAS IN THE 80S, AND THE WARMER LOWER
ELEVATIONS EAST OF THE DIVIDE IN THE LOW 90S. THE NEXT SYSTEM IS
STILL ON TRACK FOR MONDAY THROUGH WEDNESDAY NEXT WEEK, THE COLD
FRONT PUSHING THROUGH MONDAY. PRECIPITATION AMOUNTS CONTINUE TO
FLUCTUATE QUITE A BIT AS MODELS ARE STRUGGLING WITH THE SYNOPTIC
PATTERN. STILL, MUCH COOLER AND WET WILL BE THE STORY FOR EARLY NEXT
WEEK.
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 OVER 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 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 BIGHORN 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 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 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 /00Z TAFS THROUGH 00Z SATURDAY/
ISSUED AT 425 PM 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. A WEAK DISTURBANCE
IS MOVING INTO SOUTHWESTERN MT THIS AFTERNOON, AND THE RESIDUAL
MOISTURE AND SURFACE WIND CONVERGENCE HAVE INITIATED ISOLATED
TO SCATTERED SHOWERS AND THUNDERSTORMS TO AREAS OF THE WESTERN
MOUNTAINS AND SURROUNDING FOOTHILLS, ESPECIALLY TO THE SOUTH-
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 THEY MOVE TO THE SOUTHEAST OFF
THE HIGHER TERRAIN. THE CONVECTION IS EXPECTED TO CONTINUE
THROUGH 30/00-02Z. PARTLY TO MOSTLY CLOUDY OVER THE WESTERN
MOUNTAINS AND SOUTHWESTERN WY THIS EVENING WILL SLOWLY MOVE
EASTWARD OVERNIGHT WITH CLEARING IN FAR WESTERN WY FRIDAY
MORNING. SOME THIN HIGH LEVEL SMOKE HAS PUSHED IN FROM THE NORTH
THIS AFTERNOON, STAYING MAINLY EAST OF THE DIVIDE. SOME TAF
SITES WILL SEE GUSTY NORTHWEST WINDS EARLY IN THE EVENING, WITH
SOME POTENTIAL FOR 25-30 KT GUSTS DUE TO WEAK OUTFLOW FROM THE
CONVECTION.
AS THE BEFORE-MENTIONED DISTURBANCE MOVES INTO SOUTHEASTERN 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 6-8K FEET
WITH VERY ISOLATED SHOWERS IN THE MORNING, AND ISOLATED SHOWERS
AND THUNDERSTORMS EAST OF THE DIVIDE FRIDAY AFTERNOON. THE HIGH
LEVEL SMOKE IS EXPECTED TO STAY WELL TO THE EAST OVER THE
PLAINS. 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.
UPDATE...WITTMANN
DISCUSSION...HATTINGS
AVIATION...MCDONALD/LAVOIE
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