129  
FXUS65 KCYS 230551  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
1151 PM MDT TUE AUG 22 2017  
   
SHORT TERM
 
(THIS EVENING THROUGH THURSDAY NIGHT)  
ISSUED AT 1249 PM MDT TUE AUG 22 2017  
 
UPPER RIDGING IN THE NORTHERN STREAM WILL REMAIN IN PLACE OVER  
THE NORTHERN ROCKIES THROUGH THURSDAY BEFORE MIGRATING OUT INTO  
THE PLAINS ON THURSDAY NIGHT. A SOUTHERN STREAM TROUGH OFF THE  
CALIFORNIA COAST WILL DAMPEN AS IT UNDERCUTS THE RIDGE THROUGH  
THURSDAY. THIS TROUGH WILL SERVE TO START ADVECTING MORE MONSOONAL  
MOISTURE INTO THE AREA STARTING WEDNESDAY AFTERNOON AND  
CONTINUING THROUGH THURSDAY. WITH THIS INCREASE IN MOISTURE WE  
SHOULD SEE AN UPTICK IN CONVECTION WEDNESDAY ESPECIALLY OVER THE  
MOUNTAINS AND AREAS WEST OF I 25 IN SOUTHEAST WYOMING. SHEAR WILL  
BE WEAK AS THE STRONGEST MID LEVEL FLOW REMAINS WELL TO OUR NORTH  
SO DO NOT EXPECT MUCH IN THE WAY OF SEVERE THREAT. THERE IS SOME  
THREAT FOR GUSTY DOWNDRAFT PRODUCTION TOMORROW ESPECIALLY OVER  
CARBON COUNTY AS MODEL SOUNDING SHOW INVERTED-V LOW LEVEL PROFILES  
COMBINED WITH PW VALUES AROUND 0.8 INCHES.  
 
A MID LEVEL SHORTWAVE EMANATING FROM THE TROUGH OVER THE SW US WILL  
TRACK EASTWARD OVER THE CWA ON THURSDAY. INCREASED POP OVER THE  
PLAINS ON THURSDAY AS THE FAVORABLE TIMING OF THE WAVE WILL COMBINE  
WITH A SURFACE TROUGH ALONG THE LARAMIE RANGE TO PRODUCE AT LEAST  
SCATTERED CONVECTION. MLCAPE VALUES WILL RANGE FROM 500 TO 1000 J/KG  
OVER SOUTHEAST WYOMING TO AS HIGH AS 2000 J/KG OVER THE PANHANDLE.  
LOW LEVEL SE FLOW WILL BE TOPPED BY MODEST 20KT NW FLOW LEADING TO  
BULK SHEAR VALUES AROUND 30KT. THUS MAY SEE SOME STRONGER MULTI-  
CELL STORMS THURSDAY AFTERNOON WITH STRONG/GUSTY OUTFLOW WINDS AND  
SMALL HAIL BEING THE MAIN THREAT. THIS CONVECTION MAY LAST INTO THE  
LATE EVENING HOURS BEFORE THE MID LEVEL WAVE PUSHES EAST INTO  
CENTRAL NEBRASKA.  
   
LONG TERM
 
FRIDAY THROUGH TUESDAY)  
ISSUED AT 1249 PM MDT TUE AUG 22 2017  
 
MODELS IN FAIRLY GOOD AGREEMENT IN SHOWING THE UPPER LEVEL RIDGE  
BREAKING DOWN A BIT ON FRIDAY AS A WEAK MID LEVEL SHORTWAVE  
CROSSES NORTHERN WYOMING/SOUTHERN MONTANA INTO THE NORTHERN  
PLAINS. A FEW SHOWERS/THUNDERSTORMS ARE EXPECTED TO ACCOMPANY  
THIS SHORTWAVE, BUT DUE TO LACK OF MOISTURE IT WILL MOST LIKELY  
NOT BE WIDESPREAD. THIS FEATURE WILL SEND A FRONTAL BOUNDARY  
THROUGH AREAS MAINLY EAST OF THE LARAMIE RANGE ON FRIDAY WHICH MAY  
YIELD TO SOME CLOUD COVER AHEAD OF IT. BEHIND THIS SHORTWAVE,  
THINGS SHOULD DRY OUT FAIRLY QUICKLY WHICH MAY LEAD TO MORE  
CRITICAL FIRE WEATHER CONDITIONS ESPECIALLY IN AREAS WEST OF THE  
LARAMIE RANGE.  
 
BEYOND THIS TIMEFRAME, THERE IS SOME UNCERTAINTY ON HOW FAST THE  
UPPER LEVEL RIDGE BUILDS ACROSS THE WESTERN U.S. THE ECMWF/GFS ARE  
DRYING THINGS A LITTLE BIT MORE THAN THE GEM, DUE TO THE UPPER  
LEVEL RIDGE BUILDING OVER THE AREA A BIT MORE QUICKLY. EITHER WAY,  
IT APPEARS LIKE ONLY SMALL CHANCES OF SHOWERS AND THUNDERSTORMS  
WITH THOSE CHANCES FOCUSED EAST OF THE LARAMIE RANGE. AREAS ON  
THE WEST SIDE OF THE LARAMIE RANGE WILL BE LOOKING AT MOSTLY DRY  
WEATHER ALONG WITH POTENTIAL FOR CRITICAL FIRE WEATHER CONDITIONS  
THROUGH EARLY NEXT WEEK.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)  
ISSUED AT 1147 PM MDT TUE AUG 22 2017  
 
VFR CONDITIONS THROUGH THE TAF PERIOD. WITH THE LOW LEVEL JET AT  
CDR, EXPECT SOUTHERLY WINDS TO GUST TO 25 KTS THERE FOR A FEW  
MORE HOURS. ISOLATED TO SCATTERED SHOWERS/THUNDERSTORMS WILL  
DEVELOP NEAR THE SOUTHERN LARAMIE RANGE BY MID AFTERNOON. ADDED  
VCTS TO LAR/CYS WITH GUSTY OUTFLOW WINDS POSSIBLE.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 1249 PM MDT TUE AUG 22 2017  
 
DEEPLY MIXED AND DRY BOUNDARY LAYER HAS DEVELOPED  
THIS AFTERNOON OVER LOWER ELEVATIONS OF CARBON COUNTY. WINDS HAVE  
BEEN BELOW 20 MPH FOR THE MOST PART AND THIS HAS PRECLUDED THE NEED  
FOR ANY RED FLAG WARNINGS AT THIS TIME. SOME ELEVATED CONDITIONS  
ARE LIKELY THROUGH EARLY EVENING OVER WESTERN AND NORTHERN PARTS OF  
CARBON COUNTY. WITH INCREASING MOISTURE AND COOLER TEMPS WED AND  
THURS, EXPECT LITTLE IN THE WAY OF FIRE WEATHER CONCERNS. WILL NEED  
TO WATCH FOR ELEVATED CONDITIONS LATE IN THE WEEK AND THE WEEKEND AS  
DRIER AND BREEZIER CONDITIONS RETURN ESPECIALLY WEST OF THE LARAMIE  
RANGE.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...NONE.  
NE...NONE.  

 
 

 
 
SHORT TERM...DEL  
LONG TERM...REC  
AVIATION...ZF  
FIRE WEATHER...DEL  
 
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