472  
FXUS65 KRIW 200445  
AFDRIW  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE RIVERTON WY  
1045 PM MDT WED JUN 19 2019  
   
SHORT TERM
 
THIS AFTERNOON THROUGH SATURDAY  
 
SCATTERED SHOWERS AND THUNDERSTORMS HAVE STARTED THIS AFTERNOON  
ACROSS NORTHWEST WY IN ADVANCE OF THE LEFT FRONT QUAD OF THE  
UPPER LEVEL JET MOVING IN FAST FLOW OVER A LOW-LEVEL BOUNDARY  
ALONG THE MT/WY BORDER. STRONG TO POSSIBLY SEVERE STORMS ARE  
POSSIBLE LATE THIS AFTERNOON INTO THE EVENING HOURS FROM NORTH OF  
CODY ESE INTO NORTHERN JOHNSON COUNTY. THESE STORMS ARE LIKELY TO  
PRODUCE STRONG WIND AND POSSIBLY LARGE HAIL. THE SOUTHERN TWO-  
THIRDS OF THE AREA WILL CONTINUE WITH WARMER DRIER AIR AND STRONG  
WINDS WITH GUSTS UP TO 40 MPH. AS THE STORMINESS MOVES EASTWARD  
TONIGHT, THE SURFACE WIND SHOULD SHIFT TO THE NORTH THROUGH MUCH  
OF THE BIGHORN BASIN AND FROM JOHNSON INTO NATRONA COUNTY. A LARGE  
SCALE TROUGH WILL MOVE FROM SOUTHERN BRITISH COLUMBIA INTO THE  
NORTHERN ROCKIES THURSDAY, CONTINUING THE DRY SOUTHWEST FLOW INTO  
THE SOUTHERN HALF OF THE FORECAST AREA. COOLER AIR WILL APPROACH  
NORTHWEST WY BY THURSDAY EVENING, BRINGING 0C 700MB TEMPS TO YNP.  
ISOLATED SHOWERS AND THUNDERSTORMS ARE POSSIBLE THURSDAY AFTERNOON  
AND EVENING NOT ONLY ACROSS THE FAR NORTHWEST MOUNTAINS, BUT ALSO  
SWEETWATER COUNTY OFF THE UINTAS. THE GFS IS INDICATING MORE  
SHOWERS ACTIVITY ACROSS SOUTHERN WY THURSDAY EVENING. A MID- AND  
LOW- LEVEL COLD FRONT SHOULD THEN PUSH SOUTHEAST ACROSS THE AREA  
FROM THURSDAY NIGHT INTO FRIDAY MORNING, WITH 700MB TEMPS COLDER  
THAN -4C MOVING INTO NORTHWEST WY. THE LINGERING PRECIPITATION  
OVER THAT AREA WILL LIKELY BRING SNOW TO THE HIGHER ELEVATIONS OF  
YNP BY FRIDAY MORNING. THE REST OF THE AREA WILL SEE BREEZY  
NORTHWEST WIND OVERNIGHT.  
 
AN OVERALL TROUGH WILL REMAIN OVER THE NORTHERN ROCKIES WITH  
EMBEDDED SHORTWAVE TROUGHS ROTATING AROUND THE FLOW. THIS PATTERN  
WILL LIKELY KEEP BREEZY AND DRIER SOUTHWEST WIND THROUGH THE  
SOUTHERN HALF OF THE AREA, AND BREEZY WEST WIND AND SCATTERED  
SHOWERS AND THUNDERSTORMS TO THE NORTHERN HALF. FRIDAY WILL  
CERTAINLY FEEL MUCH COOLER OVER THE STATE WITH AFTERNOON  
TEMPERATURES ABOUT 15 DEGREES BELOW NORMAL. AS A STRONGER EMBEDDED  
TROUGH MOVING INTO THE GREAT BASIN SATURDAY, THE OVERALL TROUGH  
AXIS MOVES OVER THE AREA TO KEEP THE COOLER MOISTER AIR AROUND THE  
AREA. ISOLATED TO SCATTERED SHOWERS ARE LIKELY AGAIN OVER WESTERN  
AND CENTRAL WY WITH GENERALLY NORTH SURFACE WIND.  
   
LONG TERM
 
SATURDAY NIGHT THROUGH WEDNESDAY  
 
THE REMNANTS OF THE PINWHEELING UPPER LOW WILL FINALLY EXIT THE  
REGION SATURDAY NIGHT. HOWEVER, THERE WILL BE ENOUGH INSTABILITY  
IN THE AREA FOR WIDESPREAD SHOWERS AND THUNDERSTORMS SUNDAY. THE  
REST OF THE FORECAST PERIOD WILL BE MARKED BY A SLOWLY BUILDING  
RIDGE OF HIGH PRESSURE. THIS WILL BE DUE TO ANOTHER DIGGING UPPER  
LOW OFF THE PACNW COAST MONDAY AND TUESDAY. AT THE SAME TIME, A  
HIGH CENTER LINKED TO THE RIDGE WILL CONTINUE TO STRENGTHEN. BY  
TUESDAY, THIS WILL BLOCK THE UPPER LOW AND CAUSE IT TO STAGNATE AS  
THE RIDGE AXIS BUILDS OVER SOUTHERN CANADA.  
 
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE  
EVERY DAY, WITH THE BEST CHANCES OCCURRING OVER NORTHWEST PORTIONS  
OF THE FORECAST AREA. THE HOTTEST TEMPERATURES OF THE YEAR SO FAR  
COULD OCCUR BY WEDNESDAY, WITH HIGHS IN THE 90S FOR PLACES EAST OF  
THE DIVIDE AND SWEETWATER COUNTY. WARM, GUSTY SOUTHWEST WINDS WILL  
OCCUR ACROSS THE SOUTH AND THE WIND CORRIDOR TUESDAY AND  
WEDNESDAY. RELATIVE HUMIDITY VALUES WOULD APPROACH CRITICAL VALUES  
IN THIS PATTERN AS WELL. ALL OF THESE COMBINED FACTORS COULD LEAD  
TO ELEVATED FIRE CONDITIONS, DESPITE THE RECENT WET WEATHER AND  
CONTINUED GREEN UP CONDITIONS.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)  
ISSUED AT 1022 PM MDT WED JUN 19 2019  
 
SHOWER ACTIVITY IS FADING FAST ACROSS NORTHERN WYOMING THIS  
EVENING. A COUPLE SHOWERS MAY STILL BRIEFLY PASS WRL IN THE NEXT  
COUPLE HOURS, BUT IMPACTS WILL BE MINIMAL. WINDS WILL REMAIN GUSTY  
IN PLACES FOR A FEW MORE HOURS BEFORE FINALLY RELAXING DOWN TO  
AROUND 5KTS. WINDS WILL AGAIN RAMP UP DURING THE MORNING TOMORROW,  
WITH MOST SITES LIKELY TO SEE SUSTAINED WINDS AT 25KTS WITH  
FREQUENT GUSTS REACHING 40KTS. THERE WILL BE A SMALL CHANCE FOR  
SHOWERS NEAR COD/WRL DURING THE AFTERNOON, BUT CHANCES CURRENTLY  
ARE TOO LOW TO NOTE IN TAFS. GUSTY WINDS WILL CONTINUE THROUGH AT  
LEAST 06Z FOR AREAS GENERALLY WEST OF THE DIVIDE.  
 

 
   
FIRE WEATHER
 
 
STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE ACROSS NORTHERN  
WYOMING LATE THIS AFTERNOON AND EVENING. STRONG TO POSSIBLY  
DAMAGING WINDS AND LARGE HAIL WILL BE THE MAIN THREATS. ISOLATED  
THUNDERSTORMS WILL ALSO BE POSSIBLE LATE THIS AFTERNOON ACROSS  
CENTRAL PORTIONS. OTHERWISE, DRIER AND WARMER WEATHER WILL OCCUR  
OVER THE SOUTHERN HALF OF THE FORECAST AREA THIS AFTERNOON. GUSTY  
TO STRONG WINDS HAVE DEVELOPED THIS AFTERNOON OVER THESE AREAS,  
AND WILL CONTINUE THROUGH MUCH OF THE EVENING. CRITICAL RH VALUES  
WILL BE POSSIBLE OVER ZONE 279 THIS AFTERNOON. RH VALUES IN THE  
UPPER TEENS WILL ALSO OCCUR IN THE SURROUNDING ZONES, INCLUDING  
ZONE 283. MIXING AND SMOKE DISPERSAL WILL BE EXCELLENT TODAY, DUE  
TO THE HIGH WINDS. AN APPROACHING LARGE SCALE SYSTEM IN THE  
NORTHERN ROCKIES THURSDAY INTO FRIDAY WILL BRING MORE WINDY DRIER  
AIR, A CHANCE OF SHOWERS BOTH NORTH AND SOUTH, BUT COOLER  
TEMPERATURES TO THE AREA. A COLD FRONT SHOULD PUSH THROUGH  
THURSDAY NIGHT.  
 

 
   
RIW WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
SHORT TERM...MCDONALD  
LONG TERM...LAVOIE  
AVIATION...STRAUB  
FIRE WEATHER...LAVOIE/MCDONALD  
 
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