028  
FXUS65 KRIW 041847  
AFDRIW  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE RIVERTON WY  
1247 PM 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.  
 
 
   
UPDATE  
 
ISSUED AT 1245 PM MDT SUN MAY 4 2025  
 
CUMULUS ARE DEVELOPING OVER THE HIGH TERRAIN TO START THIS  
AFTERNOON. CLOUDS ARE ALSO INCREASING FROM THE SOUTH, OVER SOUTHERN  
WYOMING. SOME OF THESE CLOUDS HAVE GOTTEN BIG ENOUGH TO PRODUCE  
SHOWERS. ONLY SMALL ADJUSTMENTS WERE MADE TO THE FORECAST THIS  
AFTERNOON, WHICH WAS INCORPORATING LATEST MODEL DATA. SHOWERS AND  
THUNDERSTORMS ARE STILL EXPECTED ACROSS MUCH OF THE AREA. HOWEVER,  
THEY WILL REMAIN ISOLATED TO SCATTERED. CHANCES ARE GENERALLY 15% TO  
40%, THE BEST OF THOSE CHANCES OVER SOUTHERN AND WESTERN WYOMING, AS  
WELL AS OVER MOUNTAINS. AN ISOLATED SHOWER OR STORM IS POSSIBLE  
ALMOST ANYWHERE THOUGH. THE MAIN HAZARD WITH ANY CONVECTION REMAINS  
WINDS; GUSTS UP TO AROUND 50 MPH ARE POSSIBLE.  
 
LOOKING TO THE SPRING STORM FOR MONDAY AND TUESDAY, THE OVERALL  
THOUGHTS REMAIN CONSISTENT WITH THE PREVIOUS FORECAST (SEE FULL  
DISCUSSION BELOW). AMOUNTS HAVE INCREASED SLIGHTLY FOR THE HIGHER  
TERRAIN OF THE EAST FACING MOUNTAINS; SUCH AS THE ABSAROKAS, WIND  
RIVERS, OWL CREEKS, GREEN/RATTLESNAKES, AND CASPER MOUNTAIN.  
CONTINUING TO SEE CONVERGENCE IN THE MODELS FOR THE STAR VALLEY AREA  
MONDAY AFTERNOON AND EVENING, SO PRECIPITATION TOTALS THERE REMAIN  
SIMILAR.  
 
HAVE DROPPED TEMPERATURES SLIGHTLY FOR TUESDAY MORNING, AS MODEL  
TRENDS WOULD SUPPORT. THIS BRINGS SNOW LEVELS DOWN TO ABOUT 5500 TO  
6500 FEET, SUPPORTING SOME LOW ELEVATION SNOW. BEING MAY, WOULD NOT  
EXPECT WINTER IMPACTS, BUT TUESDAY MORNING COULD SEE SOME SNOW  
ACCUMULATE ON GRASS, WITH MAYBE EVEN MINOR ROAD/PAVEMENT  
ACCUMULATIONS. ANY SNOW SHOULD MELT PRETTY QUICKLY.  
 
 
   
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 /18Z TAFS THROUGH 18Z MONDAY/  
 
ISSUED AT 1122 AM MDT SUN MAY 4 2025  
 
PLENTY OF HIGH CLOUDS SWEEPING NORTHWARD ACROSS THE STATE  
CURRENTLY, WITH LOWER CU STARTING TO BUBBLE ACROSS SOUTHERN WY.  
SCATTERED SHOWERS SPREAD INTO THE AREA LATER THIS AFTERNOON AND  
THIS EVENING. WITH THE SCATTERED NATURE, THE PROB30 GROUPINGS  
ARE THE BEST MENTION FOR ANY PRECIP. AREAS WEST OF THE DIVIDE  
MAY SEE SOME THUNDER MIXED IN THIS AFTERNOON, BUT SHOWERS EAST  
OF THE DIVIDE WILL BE MORE PROMINENT AFTER PEAK HEATING, SO  
THUNDER MUCH LESS LIKELY.  
 
NORTH WINDS BEGIN TO SWEEP SOUTHWARD OVERNIGHT, KICKING IN MORE  
OVERRUNNING LOW CLOUDS BY EARLY MONDAY MORNING. PRECIP IS  
EXPECTED AS WELL, BUT WILL MAINLY HOLD OFF UNTIL AFTER 18Z/05.  
 
 
   
RIW WATCHES/WARNINGS/ADVISORIES  
 
NONE.  
 
 
 
 
 
UPDATE...WITTMANN  
DISCUSSION...MYERS  
AVIATION...STRAUB  
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