109
FXUS65 KRIW 300805
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
205 AM MDT FRI MAY 30 2025
KEY MESSAGES
- RATHER WARM TODAY WITH ISOLATED THUNDERSTORMS IN EASTERN
PORTIONS OF THE AREA.
- THE WARMEST WEATHER OF YEAR IS LIKELY THIS WEEKEND, WITH MANY
LOWER ELEVATIONS SEEING THE FIRST HIGHS IN THE 90S.
- A COOLER AND WETTER PATTERN MOVES IN FOR EARLY NEXT WEEK,
ALTHOUGH DETAILS OF PRECIPITATION AMOUNTS AND TIMING REMAINS
UNCERTAIN.
DISCUSSION
ISSUED AT 202 AM MDT FRI MAY 30 2025
QUIET WEATHER IS THE RULE FOR A CHANGE TONIGHT ACROSS WESTERN AND
CENTRAL WYOMING AND HERE AT THE HUMBLE RIVERTON WEATHER ABODE. MOST
AREAS SHOULD STAY MAINLY QUIET TODAY, BUT WE HAVE ONE CONCERN. THAT
IS A FAST MOVING SHORT WAVE / UPPER LEVEL LOW DIVING OUT OF
SASKATCHEWAN AND MOVING INTO THE WESTERN PLAINS STATES.
GUIDANCE HAS FINALLY COME INTO BETTER AGREEMENT IN MOVING ACROSS
MONTANA AND INTO THE DAKOTAS. THIS, PLUS THE FACT IT IS OF
CONTINENTAL ORIGIN AND AS A RESULT IS MOISTURE STARVED, WILL
KEEP ANY CONVECTION TO A MINIMUM. WE HAVE KEPT SOME MINIMAL
POPS FOR JOHNSON AND NATRONA COUNTIES AND THE EASTERN SLOPES OF
THE ABSAROKAS BUT EVEN HERE THE CHANCE OF A SHOWER OR
THUNDERSTORM IS AT MOST 1 OUT OF 5. ALL SHOWERS SHOULD END
BEFORE SUNSET. THE OTHER CONCERN IS FOR GUSTY WIND IN THE
FAVORED NORTHWEST FLOW LOCATIONS, ESPECIALLY JOHNSON COUNTY.,
WHERE THERE IS A 4 OUT OF 5 CHANCE OF WIND GUSTS PAST 40 MPH
THIS MORNING FOLLOWING THE PASSAGE OF A WEAK COLD FRONT. THE
CHANCE OF GUSTS PAST 50 MPH IS LESS THAN 1 OUT OF 10 THOUGH, SO
NO WIND HIGHLIGHTS WILL BE NEEDED. AND, WITH THE RIDGE
BUILDING, IT SHOULD KEEP THE MOST OF THE SMOKE FROM THE
WILDFIRES IN CANADA TO THE EAST OF THE AREA.
IT WILL BE A NICE AND SUMMERY START TO THE WEEKEND AND THE LAST DAY
OF METEOROLOGICAL SPRING WITH RIDGING OVER THE AREA. TEMPERATURES
WILL PUSH INTO THE 80S, IN SOME CASES WELL INTO THE 80S FOR HIGH
TEMPERATURES FOR THE LOWER ELEVATIONS. THIS COULD BE THE DAY WE SEE
OUR FIRST 90 DEGREE HIGH. HOWEVER, THERE IS A MUCH BETTER CHANCE ON
SUNDAY AS SOUTHWEST FLOW INCREASES AHEAD OF AN UPPER LEVEL LOW
APPROACHING FROM THE SOUTHWEST. MANY LOWER ELEVATION LOCATIONS WILL
HAVE AT LEAST A 1 OUT OF 2 CHANCE OF 90 DEGREES FOR A HIGH ON
SUNDAY, AND AS HIGH AS A 4 OUT OF 5 CHANCE IN THE BIG HORN BASIN.
THIS APPROACHING UPPER LEVEL LOW AND ASSOCIATED COLD FRONT WILL
ALSO INCREASE THE CHANCE OF CONVECTION. THE STORM PREDICTION
CENTER HAS ISSUED A DAY 3 MARGINAL RISK ACROSS NORTHWESTERN
WYOMING SO WE COULD SEE A FEW STRONGER STORM. AND, WE HAVE THE
CONCERN OF SOME RISING CREEK AND RIVERS AS LEFTOVER HIGH
ELEVATION SNOW MELTS. IT DOES NOT LOOK LIKE MAJOR FLOODING AT
THIS TIME BUT WE WILL WATCH IT.
WE HAVE THE SAME REASONING FOR EARLY NEXT WEEK AS YESTERDAY AT THIS
TIME. WE ARE CONFIDENT OF TRANSITIONING TO A COOLER STARTING ON
MONDAY AND CONTINUING INTO THE MIDDLE OF NEXT WEEK. HOWEVER, DETAILS
ON PRECIPITATION AMOUNTS AND TIMING OF THE PRECIPITATION REMAINS
HIGHLY UNCERTAIN. SOME GUIDANCE, LIKE THE EUROPEAN KEEPS THE ENERGY
SPLIT AND GIVES WYOMING ONLY A GLANCING BLOW FOR SHOWERS. OTHERS,
LIKE THE GFS, IS MORE IMPACTFUL WITH A DECENT RAIN MONDAY INTO
TUESDAY. PROBABILISTIC GUIDANCE STILL GIVES A GREATER THAN 1 IN
2 CHANCE OF GREATER THAN A HALF AN INCH OF QPF FOR MOST OF THE
NORTHERN HALF OF THE AREA. THERE THERE COULD BE A FEW INCHES OF
SNOW IN THE BIGHORNS, WHERE 700 MILLIBAR TEMPERATURES FALLING TO
MINUS 1 MAY LOWER SNOW LEVELS DOWN TO 8000 TO 8500 FEET ON
TUESDAY. HOWEVER, THIS SYSTEM HAS MORE MOVING PARTS THAN A RUBE
GOLDBERG MACHINE SO DETAILS WILL BE HARD TO HASH OUT UNTIL
PROBABLY SUNDAY AT THE EARLIEST. FOLLOWING THAT, THERE IS MORE
UNCERTAINTY WITH SOME GUIDANCE SHOWING RIDGING AND DRIER WEATHER
AND OTHERS HAVING ZONAL FLOW WITH SHORTWAVES BRINGING FURTHER
CHANCES OF CONVECTION. SO, UNCERTAINTY IS HIGH IN THE LONG
RANGE.
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 1000 PM MDT THU MAY 29 2025
SKIES WILL BE MOSTLY CLEAR ACROSS MUCH OF THE AREA THROUGH 12Z.
A FEW CLOUDS, CURRENTLY OVER WESTERN PORTIONS, WILL SPREAD
EASTWARD THROUGH THIS TIME AS HIGH PRESSURE BUILDS OVER THE
REGION FROM THE WEST. SMOKE ENTERED FROM THE NORTH EARLIER IN
THE AFTERNOON, BUT IS EXPECTED TO GET PUSHED OUT THROUGH 18Z AS
A RESULT OF THE BUILDING RIDGE. NO VIS RESTRICTIONS ARE
EXPECTED, BUT HAZE COULD LINGER IN THE BASINS FRIDAY AS WINDS
WILL GENERALLY STAY LIGHT. THIS WILL LIMIT THE AMOUNT OF MIXING
THAT COULD OCCUR. A FEW TERMINALS WILL HAVE GUSTS AROUND 20 KT
IN THE AFTERNOON HOWEVER. OTHERWISE, A CU FIELD WILL REDEVELOP
AFTER 18Z ONCE AGAIN (MAINLY OVER THE MOUNTAINS). ISOLATED
SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE OVER THE ABSAROKA AND
BIGHORN MOUNTAINS, WITH SOME OF THESE POSSIBLY DECOUPLING OFF
THE BIGHORNS AND MOVING OVER PORTIONS OF JOHNSON AND NATRONA
COUNTIES. NO TERMINAL IS EXPECTED TO BE DIRECTLY IMPACTED FROM
THIS ACTIVITY. ANY REMAINING CONVECTIVE ACTIVITY IS EXPECTED TO
END BY SUNSET.
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
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