605  
FXUS65 KRIW 150730  
AFDRIW  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE RIVERTON WY  
130 AM MDT WED AUG 15 2018  
   
SHORT TERM
 
TODAY THROUGH FRIDAY NIGHT  
 
OTHER THAN A FEW LIGHT SHOWERS ACROSS JOHNSON COUNTY EARLY THIS  
MORNING, ALL IS QUIET AT THIS TIME ACROSS WESTERN AND CENTRAL  
WYOMING. THE MAIN CONCERN TODAY WILL BE FOR CRITICAL FIRE WEATHER  
ACROSS SOUTHWESTERN PORTIONS OF THE AREA WITH THE COMBINATION OF LOW  
RELATIVE HUMIDITY AND A GUSTY WESTERLY BREEZE DEVELOPING. THE RED  
FLAG WARNING FOR THAT AREA LOOKS GOOD AND WILL BE CONTINUED AS IS.  
OTHERWISE, RIDGING WILL BRING A DRY AND SEASONABLE DAY.  
 
A BIT OF MOISTURE MAY TRY TO CREEP BACK INTO WESTERN WYOMING ON  
THURSDAY. THE LATEST RUN OF THE MODELS HAS REALLY BACKED OFF  
HOWEVER. AT THIS POINT, IT LOOKS LIKE ANY CONVECTION WOULD BE OF THE  
EVENING VARIETY. AND EVEN HERE, WITH THE LACK OF A TRIGGER, ANY  
COVERAGE WOULD BE ISOLATED AT BEST. WITH ANY SHOWER OR THUNDERSTORM,  
THE MAIN THREAT WOULD BE STRONG WIND GUSTS GIVEN THE DRY AIR AT THE  
LOW LEVELS OF THE ATMOSPHERE. TEMPERATURES WILL BEGIN A SLOW WARNING  
TREND AS WELL, BUT NOTHING UNUSUAL FOR THE MIDDLE OF AUGUST. WITH  
LIGHTER WIND EXPECTED, FIRE CONDITIONS SHOULD IMPROVE.  
 
A TROUGH AND COLD FRONT WILL APPROACH THE AREA ON FRIDAY. THE MODELS  
HAVE CONTINUED WITH THE TREND OF A SLOWER PROGRESSION THOUGH. AS A  
RESULT, MOST OF THE AREA SHOULD HAVE A LARGELY RAIN FREE DAY. THE  
BEST FORCING LOOKS TO BE AT NIGHT SO THERE IS THE CHANCE THIS COULD  
BE A NOCTURNAL EVENT SO WE KEPT POPS SOMEWHAT HIGHER AT NIGHT. THIS  
ALSO LOOKS TO BE THE WARMEST DAY OF THE PERIOD WITH MANY OF THE  
LOWER ELEVATIONS SEEING HIGH TEMPERATURES CLIMBING INTO THE MIDDLE  
90S FRIDAY AFTERNOON.  
   
LONG TERM
 
SATURDAY THROUGH WEDNESDAY  
 
A COMPACT UPPER LOW IS EXPECTED TO PUSH ACROSS THE FORECAST AREA  
SATURDAY AND THEN INTO THE HIGH PLAINS SATURDAY NIGHT. THE  
ASSOCIATED COLD FRONT IS EXPECTED TO PUSH ACROSS THE AREA  
SATURDAY. THERE COULD BE ONGOING CONVECTION ACROSS THE AREA  
SATURDAY MORNING ESPECIALLY OVER THE WEST/NORTHWEST SPREADING  
QUICKLY ACROSS THE ENTIRE AREA SATURDAY. THE BEST CHANCE OF  
CONVECTION STILL APPEARS TO BE ALONG AND EAST OF THE DIVIDE  
SATURDAY INTO SATURDAY EVENING. 00Z MODELS ARE PUSHING THE UPPER-  
LOW A BIT FASTER TO THE EAST WHICH CAUSES THE PRECIPITATION  
COME TO AN END SATURDAY NIGHT WITH MORE OF A FLAT RIDGE AND DRIER  
CONDITIONS SUNDAY. ALSO MODELS HAVE TRENDED WARMER WITH THIS  
SYSTEM WITH A ANY CHANGE OVER TO SNOW IN THE NORTHERN MOUNTAINS  
LATE SATURDAY NIGHT/SUNDAY CONFINED TO ABOVE 12.5 KFT MSL.  
 
MEDIUM RANGE MODELS SHOW THE POTENTIAL FOR ANOTHER COLD FRONT  
PULLING SOUTH ACROSS THE AREA MONDAY IN RESPONSE TO A SHORTWAVE  
TROUGH PULLING SOUTHEAST FROM THE CANADIAN PRAIRIES INTO THE  
NORTHERN PLAINS AND UPPER MIDWEST LATE SUNDAY INTO MONDAY. THIS  
WITH PERHAPS SOME JET ENERGY COULD GIVE PARTS OF THE AREA  
ESPECIALLY AREAS EAST OF THE DIVIDE ANOTHER CHANCE FOR SOME  
RAINFALL.  
 
TUESDAY AND WEDNESDAY, MODELS SHOW THE FORECAST AREA ON THE  
NORTHERN PERIPHERY OF A SUB-TROPICAL RIDGE WITH VARYING AMOUNTS  
OF RIDGING OVER THE FORECAST AREA. CURRENTLY LOOKS MAINLY DRY,  
BUT WOULD NOT BE SURPRISED IF SOME WEAK DISTURBANCES IN THE FLOW  
WOULD CAUSE MORE DIURNAL CONVECTION THAN CURRENTLY PROGGED BY  
GLOBAL MODELS.  
 

 
   
AVIATION
 
12Z ISSUANCE  
 
AREAS OF MVFR CEILINGS WERE DEVELOPING VICINITY KCPR-50SM W KCPR  
EARLY WEDNESDAY MORNING. THESE CEILINGS WILL LIKELY PERSIST THROUGH  
AROUND 12Z BEFORE DISSIPATING.  
 
SMOKE PLUME OVER NW WYOMING WILL LIKELY PUSH SOUTH INTO KJAC EARLY  
WEDNESDAY MORNING, BUT HIGH-RESOLUTION MODELS ARE SHOWING VISIBILITY  
REMAINING IN VFR RANGE AT KJAC WITH IMPROVING CONDITIONS IN THE  
AFTERNOON, AND POSSIBLY AN INCREASE IN SMOKE AGAIN WEDNESDAY NIGHT.  
 
OTHERWISE MAINLY SKC CONDITIONS WILL PREVAIL ACROSS THE AREA WITH  
SOME LOWER VFR VISIBILITIES IN SMOKE/HAZE 12Z WEDNESDAY-12Z  
THURSDAY.  
 

 
   
FIRE WEATHER
 
 
...RED FLAG WARNING IN EFFECT FOR SOUTHWESTERN WYOMING THIS  
AFTERNOON...  
 
THE COMBINATION OF RELATIVE HUMIDITY FALLING TO AROUND 10 PERCENT  
AND A GUSTY WESTERLY BREEZE WILL BRING THE LIKELY CRITICAL FIRE  
CONDITIONS ACROSS MUCH OF SOUTHWESTERN WYOMING THIS AFTERNOON.  
OTHERWISE, EXPECT A WARM AND DRY DAY TODAY. WIND SHOULD REMAIN LIGHT  
TO MODERATE OUTSIDE OF THE RED FLAG WARNING AREA. MIXING AND SMOKE  
DISPERSAL WILL RANGE FROM FAIR IN SOME OF THE NORTHERN BASINS TO  
EXCELLENT ACROSS SOUTHERN WYOMING.  
 

 
   
RIW WATCHES/WARNINGS/ADVISORIES
 
 
RED FLAG WARNING FROM 1 PM THIS AFTERNOON TO 8 PM MDT THIS  
EVENING FOR WYZ277>279-414.  
 

 
 

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