353
FXUS65 KRIW 041049
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
449 AM MDT SUN MAY 4 2025
KEY MESSAGES
- SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED THIS
AFTERNOON AND EVENING. STRONG OUTFLOW WINDS GUSTING 40 TO 50
MPH ARE POSSIBLE WITH THIS ACTIVITY.
- ELEVATED FIRE WEATHER CONDITIONS ARE ANTICIPATED THIS
AFTERNOON DUE TO STRONG OUTFLOW WINDS AND LOW HUMIDITY
VALUES.
- WIDESPREAD RAIN AND MOUNTAIN SNOW IS EXPECTED MONDAY THROUGH
TUESDAY, ESPECIALLY ACROSS CENTRAL WYOMING AND THE STAR VALLEY
AREA. LIGHT SNOW IS POSSIBLE (60% CHANCE) ACROSS LOWER
ELEVATIONS TUESDAY MORNING.
- PRECIPITATION MAY LEAD TO ELEVATED RIVER LEVELS TUESDAY INTO
WEDNESDAY.
DISCUSSION
ISSUED AT 432 AM MDT SUN MAY 4 2025
TODAY WILL SEE THE RIDGE THAT HAS BEEN OVER THE AREA FOR THE PAST
TWO DAYS BEGIN TO BREAK DOWN. THIS IS IN RESPONSE TO A LONGWAVE
TROUGH APPROACHING FROM THE WEST, AS WELL AS AN ASSOCIATED 500MB LOW
NOW DEEPENING ACROSS SOUTHERN CALIFORNIA. THIS WILL BRING THE
LEADING IMPACTS FROM THIS SYSTEM AS MOISTURE ADVECTS INTO WYOMING
FROM JUST ABOUT EVERY DIRECTION. WHILE DEWPOINTS WILL REMAIN LOW,
STEEP LAPSE RATES AND INCREASING DIVERGENCE ALOFT WILL HELP TO KICK
OFF SHOWERS AND THUNDERSTORMS BY EARLY AFTERNOON ACROSS WESTERN AND
SOUTHERN AREAS. THIS ACTIVITY WILL MOVE FROM SOUTHEAST TO NORTHWEST,
WITH ADDITIONAL CONVECTION DEVELOPING FARTHER NORTH AND EAST BY LATE
AFTERNOON. GIVEN THE DRY BOUNDARY LAYER AND LARGE TEMPERATURE-
DEWPOINT SPREADS, THE PRIMARY CONCERN WILL BE STRONG OUTFLOW WIND
GUSTS WITH THIS ACTIVITY; GUSTS OF 40 TO 50 MPH ARE POSSIBLE WITH
ANY SHOWER OR STORM THROUGH THE EVENING. ACCORDINGLY, MUCH OF
THE PRECIPITATION WILL NOT REACH THE GROUND TODAY, ESPECIALLY
EAST OF THE DIVIDE WHERE TEMPERATURES WILL PEAK 15 TO 20 DEGREES
ABOVE NORMAL. THE OVERALL DRY CONDITIONS AND STRONG CONVECTIVE
OUTFLOW POTENTIAL WILL LEAD TO ELEVATED FIRE WEATHER CONDITIONS
TODAY.
PRECIPITATION WILL END AROUND MIDNIGHT TONIGHT. THE LOW WILL THEN
MOVE EAST OVER THE ARIZONA/NEW MEXICO BORDER OVERNIGHT, BEFORE
DRIFTING AND EXPANDING OVER THE FOUR CORNERS REGION THROUGH TUESDAY.
THE WILL BE THE IMPETUS FOR A RESPECTABLE PRECIPITATION EVENT OVER
WYOMING THROUGH THIS TIME. RAIN AND MOUNTAIN SNOW WILL BEGIN TO
DEVELOP BY EARLY MONDAY AFTERNOON, BECOMING WIDESPREAD MONDAY
EVENING, AND THEN CONTINUING THROUGH TUESDAY. WITH A FAVORABLE
NORTHEASTERLY UPSLOPE FLOW, THE HIGHEST AMOUNTS ARE EXPECTED EAST OF
THE DIVIDE, ESPECIALLY IN THE LANDER FOOTHILLS AND CASPER AREAS.
FORECAST PRECIPITABLE WATER VALUES ARE STILL OVER 0.60", WHICH WOULD
PUT IT NEAR THE CLIMATOLOGICAL MAXIMUM FOR THIS TIME OF YEAR AT KRIW
(SPC SOUNDING CLIMATOLOGY).
HOWEVER, RECENT TRENDS WITH THE LOW STAYING A LITTLE FARTHER SOUTH
HAVE RESULTED IN QPF DECREASING A BIT. PRECIPITATION AMOUNTS ACROSS
CENTRAL WYOMING ARE GENERALLY IN THE 0.40" TO 0.9" RANGE, WITH THE
HIGHER VALUES TOWARD THE NORTHEASTERLY FACING MOUNTAIN SLOPES. THIS
INCLUDES THE LANDER AND CASPER AREAS, WHICH CURRENTLY HAVE ABOUT A
50% CHANCE OF SEEING AT LEAST 1" OF PRECIPITATION DURING THE PERIOD
FROM MONDAY THROUGH TUESDAY. ON THE FLIP SIDE, ONE LOCATION THAT HAS
TRENDED UP WITH QPF RECENTLY IS STAR VALLEY. THIS APPEARS TO BE DUE
TO AN EMBEDDED SHORTWAVE AT THE TOP OF THE TROUGH DROPPING IN FROM
MONTANA MONDAY AFTERNOON, LEADING TO A PERIOD OF CONVERGENCE OVER
EASTERN IDAHO AND WESTERN WYOMING. CURRENTLY, THE STAR VALLEY AREA
HAS AROUND A 60% CHANCE OF SEEING AT LEAST 1" OF PRECIPITATION,
MAINLY FROM MONDAY AFTERNOON THROUGH MONDAY NIGHT.
ELSEWHERE, ACCUMULATIONS ARE GENERALLY EXPECTED TO BE UNDER HALF AN
INCH. 700MB TEMPERATURES APPROACHING NEGATIVE 7C TUESDAY MORNING
CERTAINLY MEAN MOUNTAIN SNOW, AND LIKELY EVEN A CHANGE TO ALL
SNOW FOR A TIME IN THE LOWER ELEVATIONS AS WELL. IF A CHANGEOVER
TO SNOW DOES OCCUR TUESDAY MORNING, IT VERY WELL MAY LAST
THROUGH MOST OF THE MORNING AS TEMPERATURES STRUGGLE TO WARM.
HOWEVER, ACCUMULATIONS WOULD LIKELY BE LIMITED TO ELEVATED OR
VEGETATED SURFACES, AND WIDESPREAD WINTER WEATHER IMPACTS ARE
NOT EXPECTED. THE PRIMARY CONCERN WITH THIS EVENT IS THE
POTENTIAL FOR RIVER AND SMALL STREAM FLOODING. ELEVATED RIVER
LEVELS CAN BE EXPECTED, AIDED IN PART BY THE WARM WEEKEND
PRECEDING THE RAIN.
PRECIPITATION WILL COME TO AN END TUESDAY EVENING. FURTHER AHEAD,
ENSEMBLE CLUSTER GUIDANCE CONTINUES TO INDICATE A QUICK RETURN TO
RISING 500MB HEIGHTS BY WEDNESDAY. THIS FAVORS WARMER AND DRIER
CONDITIONS THROUGH THE END OF NEXT WEEK.
AVIATION /12Z TAFS THROUGH 12Z MONDAY/
ISSUED AT 402 AM MDT SUN MAY 4 2025
PREVAILING VFR CONDITIONS AND LIGHT WIND (LESS THAN 10 KNOTS)
THROUGH 20Z SUNDAY. CONVECTION WILL BEGIN DEVELOPING SUNDAY
AFTERNOON. SHOWERS AND STORMS WILL PERSIST WELL INTO THE EVENING
HOURS SUNDAY BEFORE FINALLY DISSIPATING AROUND 08Z SUNDAY
NIGHT. MOST RAIN WILL NOT REACH THE GROUND, BUT HAVE INCLUDED
PROB30 GROUPS FOR POSSIBLE MVFR VIS IF A STRONGER CELL MOVES
DIRECTLY OVER THE TERMINAL. TERMINALS WITH PROB30 WITH
THUNDERSTORMS CHANCES ARE KBPI, KPNA, KJAC, AND KRKS. ANY OF
THESE STORMS COULD HAVE STRONG WIND GUSTS WITH THE DRY
ATMOSPHERE. WITH RECENT MODEL TRENDS, WE HAVE ALSO INCLUDED KCOD
AND KWRL WITH PROB30 GROUPS FOR SHOWERS. ALL LOCATIONS HAVE
AROUND 1 IN 6 CHANCE OF A SHOWER OR THUNDERSTORM, BUT NOT
ENOUGH CONFIDENCE TO INCLUDE IN THE TAFS AT THIS TIME. WIND
SHOULD REMAIN MODERATE AT MOST LOCATIONS OUTSIDE OF
THUNDERSTORMS THROUGH 06Z MONDAY, WITH THE EXCEPTIONS OF KBPI,
KPNA, KCPR AND KRKS WHERE WIND GUSTS OVER 20 KNOTS ARE POSSIBLE.
GUSTY NORTH TO NORTHEASTERLY WIND AFTER 06Z MONDAY IS LIKELY AT
MOST TAF LOCATIONS EAST OF THE DIVIDE FOLLOWING THE PASSAGE OF
A COLD FRONT.
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...MYERS
AVIATION...HATTINGS
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