822
FXUS65 KRIW 231852
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1252 PM MDT SAT MAY 23 2026
KEY MESSAGES
- MEMORIAL DAY WEEKEND STARTS OFF VERY NICE ACROSS WESTERN AND
CENTRAL WYOMING TODAY, WITH MOSTLY CLEAR TO PARTLY CLOUDY
SKIES, ISOLATED SHOWERS ACROSS NORTHERN WY, TEMPERATURES 4-8
DEGREES ABOVE NORMAL IN THE 70S FOR THE LOWER ELEVATIONS, AND
BREEZY WEST WINDS OVER THE MOUNTAINS AND SOUTHERN 2/3 OF THE
STATE.
- TEMPERATURES CONTINUE TO WARM ON SUNDAY FROM THE MID 70S TO
MID 80S (5-10 DEG ABOVE NORMAL). CLOUDS WILL INCREASE FROM THE
SOUTH-SOUTHWEST DURING THE DAY, WITH ISOLATED TO SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS OVER THE SOUTHERN 2/3 OF
WESTERN AND CENTRAL WY. AFTERNOON WINDS WILL AGAIN BE BREEZY
AND GUSTY OUT OF THE WEST.
- MEMORIAL DAY WILL SEE TEMPERATURES CLIMB A FEW MORE DEGREES AS
SOUTHERLY WINDS INCREASE. ISOLATED TO SCATTERED SHOWERS WITH
ISOLATED THUNDERSTORMS ARE EXPECTED IN THE AFTERNOON AND EARLY
EVENING, WITH SOUTHWEST AND WESTERN WY HAVING THE BEST
CHANCES.
- SCATTERED TO WIDESPREAD SHOWERS AND THUNDERSTORMS ARE ALSO
EXPECTED ON TUESDAY. A COOLER AND WETTER PATTERN IS EXPECTED
FOR THE REST OF THE WEEK, THOUGH UNCERTAINTY REMAINS HIGH ON
THE DETAILS BASED ON THE MOVEMENT OF A LARGE LOW-PRESSURE
SYSTEM.
UPDATE
ISSUED AT 1250 PM MDT SAT MAY 23 2026
WEST-NORTHWEST MID-LEVEL FLOW CONTINUES TO BRING PARTLY CLOUDY
TO MOSTLY CLEAR SKIES TO WESTERN AND CENTRAL WYOMING TODAY,
ALONG WITH LIGHT TO BREEZY WINDS. VERY ISOLATED SHOWERS ARE
POSSIBLE OVER THE NORTHERN TO CENTRAL PORTIONS OF THE BIGHORN
MOUNTAINS THIS AFTERNOON. THEN, A VERY WEAK POCKET OF ENERGY
COULD PRODUCE SOME ISOLATED SHOWERS OVER THE NORTHERN PARTS OF
YELLOWSTONE AND THE ABSAROKA MOUNTAINS LATE THIS AFTERNOON AND
INTO THE EVENING HOURS. TEMPERATURES ARE QUITE PLEASANT TODAY TO
START OFF THE MEMORIAL DAY WEEKEND, REACHING THE UPPER 60S TO
MID 70S IN THE LOWER ELEVATIONS (A FEW DEGREES ABOVE NORMAL).
WINDS ARE EXPECTED TO DECREASE BETWEEN SUNSET AND MIDNIGHT.
SUNDAY WILL SEE CLOUDS INCREASING FROM THE WEST AS A SHORTWAVE
TROUGH FROM THE NORTHERN GREAT BASIN MOVES EASTWARD ACROSS
WYOMING. AFTERNOON TEMPERATURES THOUGH SHOULD INCREASE A FEW
MORE DEGREES OVER SATURDAY FOR HIGHS IN THE 70S TO MID 80S.
MODELS ARE INDICATING ISOLATED TO SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS TO DEVELOP IN THE AFTERNOON FROM ABOUT THE TETONS
SOUTHWARD TO SOUTHWEST WY. THE CONVECTION WILL THEN MOVE
EASTWARD THROUGH THE AFTERNOON AND EVENING. HIGH-RESOLUTION
MODELS ARE TARGETING SWEETWATER COUNTY INTO THE UPPER GREEN
RIVER BASIN AND SOUTH PASS FOR THE MOST LIKELY AREAS OF
STORMINESS. THE WEST SIDE OF THE WIND RIVERS AROUND PINEDALE
COULD SEE ENHANCED CONVECTIVE ACTIVITY ACCORDING TO THE RRFS,
NAMNEST, AND MPAS. ALONG WITH SOME BRIEF MODERATE RAIN, GUSTY
OUTFLOWS OVER 40 MPH ARE POSSIBLE. GENERALLY, BREEZY WEST-
SOUTHWEST WINDS ARE EXPECTED FOR MOST AREAS DURING THE AFTERNOON
AND EARLY EVENING.
DISCUSSION
ISSUED AT 247 AM MDT SAT MAY 23 2026
WE HAVE NOW ENTERED THE UNOFFICIAL START OF SUMMER (FOR TOURIST
REASONS ANYWAY, METEOROLOGICAL SUMMER STARTS JUNE 1 AND ASTRONOMICAL
SUMMER ON JUNE 21). AND IN WESTERN AND CENTRAL WYOMING, MEMORIAL DAY
WEEKEND IS TRADITIONALLY BY FAR THE WETTEST OF THE THREE MAIN
HOLIDAY THREE DAY WEEKENDS. A GRAPHIC WE POSTED A FEW YEARS AGO
SHOWS GREATER THAN HALF OF OUR MAIN CLIMATE SITES HAVE HAD AT LEAST
HALF OF MEMORIAL DAYS SINCE 2003 HAD HAD AT LEAST SOME RAIN. IN MY
14 YEARS AT THIS OFFICE, I HAVE SEEN EVERYTHING FROM 90 DEGREE HEAT
TO SEVERE THUNDERSTORMS TO EVEN SNOW AT THE OFFICE. THIS WEEKEND
WILL BE ON THE DRIER END, BUT NOT COMPLETELY DRY. AND RAIN CHANCES
WILL INCREASE AS THE WEEKEND PROGRESSES.
A SUBTLE SHORTWAVE IS MOVING ACROSS NORTHERN PORTIONS OF WYOMING,
AND WE DO HAVE SOME RETURNS ON RADAR. MANY OF THESE ARE PROBABLY NOT
REACHING THE GROUND THOUGH. A FEW OF THE LATEST HI RESOLUTION MODEL
RUNS DO SHOW A FEW SHOWERS THIS AFTERNOON. HOWEVER, PRECIPITABLE
WATER VALUES ARE BELOW NORMAL (GENERALLY 60 TO 80 PERCENT OF
NORMAL). THIS BEING A HOLIDAY WEEKEND, WE DID ADD A 1 IN 5 CHANCE OF
SHOWERS BUT ONLY OVER THE MOUNTAINS AND EVEN HERE MOST SHOWERS WOULD
BE HIGH BASED WITH MODEL SOUNDINGS SHOWING INVERTED V SIGNATURES, SO
MOST WOULD END UP AS VIRGA SHOWERS. THESE COULD PRODUCE STRONG WIND
GUSTS THOUGH. HOWEVER, A VAST MAJORITY OF THE AREA SHOULD STAY DRY
WITH JUST SOME AFTERNOON CUMULUS BUILDUP. I ALSO CAN'T RULE OUT A
BUT OF THUNDER, BUT IT WOULD BE VERY ISOLATED SO WE LEFT IT OUT OF
THE FORECAST FOR NOW. TEMPERATURES SHOULD RUN CLOSE TO SEASONAL
AVERAGES WITH A BIT OF AN AFTERNOON BREEZE, BUT NOTHING UNUSUAL FOR
WYOMING. ANY SHOWERS SHOULD END FAIRLY QUICKLY AFTER SUNSET WITH DRY
CONDITIONS SATURDAY NIGHT.
FLOW TURNING SOUTHWEST WILL WARM TEMPERATURES TO ABOVE NORMAL LEVELS
FOR SUNDAY. CHANCES OF SHOWERS WILL BEGIN TO RISE ON THIS DAY THOUGH
WITH ANOTHER SHORTWAVE MOVING THROUGH. PRECIPITABLE WATER VALUES
BEGIN TO RISE THIS DAY, BUT NOT AN EXTREME AMOUNT. THEY DO RISE TO
ABOVE NORMAL LEVELS ACROSS SOUTHERN WYOMING AS SOUTHWEST FLOW BRINGS
IN SOME INCREASED MOISTURE, BUT REMAIN NEAR TO BELOW NORMAL IN
NORTHERN WYOMING. WITH THIS, ANY CONVECTION WAS KEPT LARGELY ACROSS
THE SOUTHERN HALF OF THE STATE. COVERAGE STILL LOOKS FAIRLY SPARSE,
GENERALLY A 1 IN 3 CHANCE OR LESS IN ANY PARTICULAR LOCATION. AGAIN,
THIS WILL BE LARGELY DIURNAL WITH ALMOST ALL SHOWERS ENDING SHORTLY
AFTER MIDNIGHT. MONDAY AT THIS POINT LOOKS FAIRLY SIMILAR, WITH MOST
SHOWERS BEING CONFINED TO SOUTHERN AND WESTERN WYOMING WITH DRY AIR
HOLDING IN THE LOWER LEVELS AREAS FURTHER NORTH AND EAST FOR ANOTHER
DAY.
THINGS GET MORE UNCERTAIN AS WE HEAD INTO NEXT WEEK. AND THE REASON
WHY WILL BE WHAT HAPPENS WITH A BIG ATMOSPHERIC BOWLING BALL, A.K.A.
AN UPPER LEVEL LOW, THAT WILL BE MOVING ONSHORE IN THE PACIFIC
NORTHWEST ON MONDAY AND PROGRESSING ONSHORE. IT WILL BE A SLOW MOVER
AS WELL, AS IT IS RATHER VERTICALLY STACKED AND MAY END UP CUTTING
OFF. THE BIG X FACTOR IS WHAT WILL HAPPEN FURTHER TO THE EAST. A
VERY STRONG RIDGE WILL BE BUILDING ACROSS THE NORTHERN UNITED
STATES, POSSIBLY DEVELOPING INTO A BLOCKING RIDGE. THE QUESTION IS
WHERE WILL IT SET UP AS THIS WILL DETERMINE THE MOVEMENT OF THE LOW.
SOME ENSEMBLE MEMBERS, AS WELL AS THE DETERMINISTIC GFS, SHOW THE
RIDGE AXIS CLOSER TO THE GREAT LAKES. THIS WOULD ALLOW THE UPPER
LEVEL LOW FURTHER EAST, BRINGING DEEPER MOISTURE TO THE COWBOY
STATE, WITH PRECIPITABLE WATER LEVELS RISING AS HIGH AS 150 PERCENT
OF NORMAL AND BETTER CHANCE OF SHOWERS AND THUNDERSTORMS. OTHER
ENSEMBLE MEMBERS, AS WELL AS THE DETERMINISTIC EUROPEAN, KEEP THE
RIDGE AXIS FURTHER WEST, WHICH WOULD HOLD THE LOW AND DEEPER
MOISTURE FURTHER WEST, RESULTING IN A DRIER AND WARMER PATTERN. AT
THIS POINT, WHICH WOULD OCCUR IS BASICALLY A COIN FLIP. PERIODS OF
HEAVIER SHOWERS WOULD BE DETERMINED BY SHORTWAVES ROTATING AROUND
THE LOW. AT THIS POINT, THE FORECAST THIS FAR OUT HAS MORE MOVING
PARTS THAN A RUBE GOLDBERG MACHINE SO DETAILS ARE DIFFICULT. AT THIS
POINT, THE END OF NEXT WEEK, LIKE THURSDAY AND FRIDAY WOULD BE MORE
FAVORED BUT PLACEMENT OF HEAVIEST PRECIPITATION IS IMPOSSIBLE THIS
FAR OUT. THERE IS A REASON OLD TIME FORECASTERS CALLED UPPER LEVEL
LOWS "UPPER LEVEL DEVILS". STAY TUNED.
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1109 AM MDT SAT MAY 23 2026
VFR CONDITIONS THROUGH THE PERIOD. WESTERLY WINDS INCREASE FOR THE
AFTERNOON, DECREASING THIS EVENING, FOLLOWING TYPICAL DIURNAL
TRENDS. HIGH CLOUDS PASS THROUGH, WITH SOME MID-LEVEL CUMULUS ALSO
OCCURRING THIS AFTERNOON. SOME VERY LIGHT SHOWERS, OR VIRGA SHOWERS,
WILL ALSO OCCUR THIS AFTERNOON, MAINLY FORMING OVER THE HIGHER
TERRAIN. A FEW COULD MOVE OFF THE MOUNTAINS AND INTO THE NEARBY
LOWER ELEVATIONS, SUCH AS AROUND KCOD (25% CHANCE) OR KRKS (15%
CHANCE); OTHER SITES ARE 10% OR LESS. A GUSTY OUTFLOW WIND UP TO 35
MPH IS THE MAIN HAZARD WITH THESE. MID-LEVEL MOISTURE SHOULD KEEP
SOME CLOUDS OVERNIGHT.
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...MCDONALD
DISCUSSION...HATTINGS
AVIATION...WITTMANN
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