615  
FXUS65 KRIW 251751 AAA  
AFDRIW  
 
AREA FORECAST DISCUSSION...UPDATE  
NATIONAL WEATHER SERVICE RIVERTON WY  
1151 AM MDT THU MAY 25 2017  
   
SHORT TERM
 
THURSDAY THROUGH SATURDAY NIGHT  
 
THERE CERTAINLY WERE SOME STRONG WIND GUSTS YESTERDAY AS THE FRONT  
BLEW THROUGH THE AREA. IN ADDITION, THUNDERSTORMS DEVELOPED AS THE  
FRONT SAGGED SOUTHWARD AND INTERACTED WITH THE RIGHT REAR QUADRANT  
OF A JET STREAK. AS OF AROUND MIDNIGHT WE STILL HAVE SOME  
CONVECTION BUT IT IS SLOWLY WEAKENING AS WE LOSE THE UPPER LEVEL  
SUPPORT. BY MORNING, THERE WILL STILL BE SOME SHOWERS AROUND IN  
SOUTHERN AREAS BUT NOTHING HEAVY IS EXPECTED.  
 
AS FOR TODAY, IT LOOKS MUCH QUIETER WITH THE FRONT TO THE SOUTH OF  
THE AREA. WITH THE BOUNDARY NEAR THE SOUTHERN BORDER, THERE WILL  
STILL BE SOME SHOWERS AND THUNDERSTORMS ALONG THE SOUTHERN BORDER.  
IN ADDITION, ANOTHER WEAK SHORTWAVE MOVING THROUGH MONTANA MAY  
BRING A FEW THUNDERSTORMS TO THE WESTERN AND NORTHERN MOUNTAINS.  
HOWEVER, COVERAGE WILL BE LESS THAN YESTERDAY AS A RULE. WITH  
COOLER TEMPERATURES AND LOWER WET BULB ZERO LEVELS, THE MAIN  
THREAT WILL SHIFT TO SMALL HAIL. IN ADDITION, STEERING FLOW ACROSS  
THE NORTH WILL BE RATHER LIGHT SO MOST STORMS SHOULD STAY IN THE  
MOUNTAINS. THE MOST NOTICEABLE THINGS WILL BE LESS WIND AND  
COOLER TEMPERATURES FOR MOST PEOPLE.  
 
FRIDAY AT THIS POINT LOOKS TO BE THE WETTEST OF THE THREE DAYS  
ACROSS THE AREA. A MID LEVEL AREA OF LOW PRESSURE IS EXPECTED TO  
DEVELOP AND MOVE ACROSS WYOMING. THIS WILL LIKELY TURN FLOW TO THE  
NORTHEAST AND INCREASE UPSLOPE ACROSS THE AREA. THIS WILL LEAD TO  
A COOL AND CLOUDY DAY WITH PERIODS OF SHOWERS AND POSSIBLY A  
THUNDERSTORM, ALTHOUGH HEAVY AMOUNTS OF PRECIPITATION ARE NOT  
EXPECTED AT THIS TIME. AND YES, IT WILL LIKELY BE COLD ENOUGH FOR  
SOME OF THAT PRECIPITATION TO FALL AS SNOW IN THE MOUNTAINS. THIS  
STEADIER PRECIPITATION SHOULD END ACROSS THE AREA LATER FRIDAY  
NIGHT.  
 
FOR THE START OF THE MEMORIAL DAY WEEKEND, THERE SHOULD SOME  
IMPROVEMENT IN THE WEATHER. TEMPERATURES SHOULD BEGIN A GRADUAL  
WARMING TREND WITH CHANCES OF PRECIPITATION DECREASING. HOWEVER,  
NOTICE HOW I SAID DECREASING, NOT ENDING. WITH NORTHWEST FLOW ACROSS  
THE AREA, THERE WILL BE A CHANCE OF MAINLY AFTERNOON AND EVENING  
THUNDERSTORMS ACROSS THE AREA EACH DAY. HOWEVER, THEY SHOULD BE  
FAIRLY SPARSE WITH MOST AREAS DRY MOST OF THE TIME. AND AS IT IS  
WITH CONVECTION, IT WILL BE VERY DIFFICULT TO PINPOINT WHERE THE  
STORMS POP UP.  
   
LONG TERM
 
SUNDAY THROUGH THURSDAY  
 
A RELATIVELY MOIST NORTHWEST FLOW WILL BE ACROSS THE AREA THROUGH  
TUESDAY BETWEEN AN UPPER RIDGE OVER THE WEST COAST/INTERMOUNTAIN  
WEST, AND A LONGWAVE TROUGH OVER THE CENTRAL/EASTERN U.S. MODELS  
SHOW ENOUGH MOISTURE AND INSTABILITY WITH PEAK HEATING FOR DAILY  
SHOWERS AND THUNDERSTORMS FORMING OVER THE MOUNTAINS AND TRYING  
TO PUSH SOUTHEAST INTO THE BASINS/VALLEYS. THIS ACTIVITY COULD BE  
ENHANCED AT TIMES WITH SOME SUBTLE WAVES IN THE FLOW AND LOCAL  
CONVERGENCE ZONES. ANOTHER CONCERN IS FOR CONVECTION TO PUT OUT  
GUSTY OUTFLOWS WELL AWAY FROM THEIR PARENT CONVECTION WHICH COULD  
CAUSE CHOPPY LAKES AND RESERVOIRS FROM DISTANT THUNDERSTORMS.  
 
BY WEDNESDAY AND THURSDAY, MODELS ARE GENERALLY SHOWING A FLAT  
RIDGE SLIDING EAST ACROSS THE NORTHERN ROCKIES AS A SHORTWAVE  
TROUGH/UPPER LOW DIGS OFF THE PACIFIC NORTHWEST COAST. STILL  
ENOUGH MOISTURE AND INSTABILITY FOR AT LEAST DIURNAL DRIVEN  
MOUNTAIN CONVECTION POSSIBLY PUSHING INTO THE LOWER ELEVATIONS.  
 
TEMPERATURES ARE EXPECTED TO BE SEASONAL EARLY NEXT WEEK BECOMING  
5 TO 10 DEGREES ABOVE AVERAGE BY MID-WEEK  
 

 
   
AVIATION
 
18Z ISSUANCE  
 
WEST OF THE CONTINENTAL DIVIDE...KBPI/KJAC/KPNA/KRKS TERMINALS  
 
THE LAST OF THE AREA OF THUNDERSTORMS OVER EXTREME SOUTHERN  
SWEETWATER COUNTY WILL BE EXITING THE AREA SHORTLY. AN UPPER LEVEL  
DISTURBANCE WILL MOVE ACROSS THE NORTHERN GREAT BASIN INTO SW  
WYOMING THIS AFTERNOON. SCATTERED SHOWERS AND THUNDERSTORMS ARE  
EXPECTED TO REMAIN SOUTH OF KRKS TOWARD THE UTAH/COLORADO BORDER,  
MOVING NE INTO SOUTH CENTRAL AND SOUTHEAST WYOMING. ISOLATED SHOWERS  
WILL BE CONFINED MAINLY TO THE MOUNTAINS FURTHER NORTH THIS  
AFTERNOON AND EVENING. A SECOND UPPER LEVEL DISTURBANCE WILL BRING  
INCREASING CLOUDS AND SHOWERS INTO FAR WEST WYOMING EARLY FRIDAY  
MORNING WITH AREAS OF MVFR AND LCL IFR CONDITIONS ALONG WITH MTN  
OBSCN.  
 
EAST OF THE CONTINENTAL DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL TERMINALS  
 
A NORTHERLY LOW LEVEL FLOW AND SLIGHT INSTABILITY WILL RESULT IN  
INCREASING CUMULUS AND ISOLATED SHOWERS AND THUNDERSTORMS THIS  
AFTERNOON INTO EARLY EVENING, WITH MOST OF THIS ACTIVITY IN THE  
VICINITY OF THE CONTINENTAL DIVIDE, VICINITY KCOD-KLND AND ALONG THE  
BIGHORN MOUNTAINS. SHOWERS AND ISOLATED THUNDERSTORMS WILL  
DISSIPATE AROUND SUNSET. UPSLOPE EASTERLY FLOW MAY RESULT IN AREAS  
OF MVFR, LOCAL IFR CEILINGS DEVELOPING EARLY FRIDAY MORNING,  
VICINITY KCPR-KLND.  
 

 
   
FIRE WEATHER
 
 
TODAY WILL BE A MUCH COOLER DAY FOLLOWING THE PASSAGE OF A COLD  
FRONT. TEMPERATURES WILL AVERAGE 15 TO 20 DEGREES COOLER FOR MOST  
AREAS. RELATIVE HUMIDITY WILL ALSO BE HIGHER AND REMAIN ABOVE  
CRITICAL LEVELS FOR ALL AREAS. WIND SHOULD REMAIN LIGHT TO MODERATE  
FOR MOST AREAS BUT COULD REMAIN GUSTY IN PORTIONS OF SOUTHWESTERN  
WYOMING. MIXING AND SMOKE DISPERSAL WILL BE GENERALLY GOOD TO VERY  
GOOD. AN APPROACHING AREA OF LOW PRESSURE COULD BRING A WETTING RAIN  
TO SOME AREA FRIDAY WITH SOME SNOW POSSIBLE IN THE HIGHER  
ELEVATIONS.  
 

 
   
RIW WATCHES/WARNINGS/ADVISORIES
 
NONE.  
 

 
 

 
 
SHORT TERM...HATTINGS  
LONG TERM...MURRELL  
AVIATION...MEUNIER/LIPSON  
FIRE WEATHER...HATTINGS  
 
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