851  
FXUS65 KCYS 281143  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
543 AM MDT WED JUN 28 2017  
   
SHORT TERM
 
(TODAY THROUGH THURSDAY NIGHT)  
ISSUED AT 252 AM MDT WED JUN 28 2017  
 
AREA WILL REMAIN UNDER THE INFLUENCE OF AN UPPER TROUGH OVER  
ALBERTA THROUGH THURSDAY. WEAK SHORTWAVE ENERGY WILL TRACK OVER  
OUR NORTHERN COUNTIES THIS AFTERNOON AS A 90KT UPPER JET NOSES  
INTO NORTHERN CO. AT THE SURFACE, A WEAK FRONT WILL REMAIN NEARLY  
STATIONARY OR SLOWLY WASH OUT JUST TO OUR SOUTH. THIS WILL SET THE  
STAGE FOR MORE AFTERNOON CONVECTION TODAY. MODEL FORECAST  
SOUNDINGS ONCE AGAIN INDICATE A DEEPLY MIXED BOUNDARY LAYER TOPPED  
BY WEAK INSTABILITY WITH MUCAPE ON THE ORDER OF 500 TO 1000 J/KG.  
WITH GREAT EVAPORATIVE COOLING POTENTIAL, THINK STRONG AND GUSTY  
DOWNDRAFTS ARE ONCE AGAIN A POSSIBILITY WITH JUST ABOUT ANY  
CONVECTION THIS AFTERNOON. MOST ACTIVITY WILL BE CONCENTRATED OVER  
OUR NORTHERN COUNTIES WHERE THE BEST LOW LEVEL CONVERGENCE AND  
PROXIMITY TO FORCING ALOFT ARE LOCATED WITH ANOTHER AREA OF  
DEVELOPMENT ALONG AND JUST NORTH OF THE FRONTAL BOUNDARY OVER NE  
CO. FORCING BOTH AT THE SURFACE AND ALOFT NOT AS STRONG AS  
YESTERDAY BUT STILL WOULD NOT BE SURPRISED TO SEE A FEW SEVERE  
WIND REPORTS FROM THE ACTIVITY THIS AFTERNOON.  
 
MODELS SHOW A WEAK FRONT PASSING ACROSS THE AREA FROM THE NW TONIGHT  
AND WITH SOME ELEVATED CAPE STILL PRESENT, MAINTAINED SOME POP EVEN  
INTO THE NIGHT TIME HOURS.  
 
A STRONGER SHORTWAVE AND ITS ATTENDANT COLD FRONT WILL MOVE ACROSS  
THE AREA ON THURSDAY. STEEPENING LAPSE RATES UNDERNEATH COOL AIR  
ALOFT WILL PROMOTE CONTINUED CHANCES FOR SHOWER AND THUNDERSTORM  
ACTIVITY BUT THINK THE WIND THREAT WILL BE A BIT LOWER DUE TO COOLER  
TEMPS AND LESS OF A T/TD SPREAD IN THE BL. SOME HAIL WILL BE  
POSSIBLE WITH THE STRONGER STORMS AS FREEZING LEVELS LOWER AND  
MID/UPPER TROPOSPHERIC FLOW REMAINS STRONG. COOLER AND MORE STABLE  
AIR WILL FILTER INTO THE AREA BEHIND THE FRONT ON THURSDAY NIGHT.  
   
LONG TERM...(FRIDAY THROUGH WEDNESDAY)
 
 
ISSUED AT 252 AM MDT WED JUN 28 2017  
 
WARMING AND GENERALLY DRY CONDITIONS CAN BE EXPECTED THROUGH THE  
PERIOD AS SWIFT NORTHWEST FLOW GIVES WAY TO BUILDING HEIGHTS BENEATH  
A STRENGTHENING FOUR CORNERS HIGH. H7 TEMPERATURES OF AROUND 3C ON  
FRIDAY ARE PROGD TO WARM INTO THE 15-18C RANGE BY THE MIDDLE OF NEXT  
WEEK. FORECASTED TEMPERATURES WILL REFLECT THIS TREND WITH HIGHS IN  
THE 70S ON FRIDAY GIVING WAY TO 80S TO AROUND 90F SUN-WED. LATEST  
DETERMINISTIC MODEL RUNS EVEN SUGGEST THAT THESE VALUES ARE  
CONSERVATIVE AND WILL NEED TO BE INCREASED WITH TIME. EXPECT  
GENERALLY DRY CONDITIONS TO PREVAIL, WITH THE EXCEPTION OF ISOLATED  
SHOWER & THUNDERSTORM CHANCES SUNDAY AFTERNOON AS A WEAK SHORTWAVE  
MOVES THRU DURING PEAK HEATING.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)  
ISSUED AT 543 AM MDT WED JUN 28 2017  
 
FORECAST CHALLENGES TO AVIATION OPS TODAY WILL BE THE TIMING AND  
COVERAGE OF AFTERNOON AND EVENING -SHRAS/-TSRAS. LATEST GUIDANCE  
SUGGESTS THUNDERSTORMS TO BEGIN DEVELOPING NEAR KCYS AND  
ASSOCIATED ROUTES BY 21Z, SHIFTING EAST INTO WESTERN NEBRASKA  
TERMINALS THROUGH 02-04Z. SOME INDICATIONS THAT SOME RE-  
DEVELOPMENT WILL OCCUR PERHAPS LINGERING CONVECTION INTO THE  
OVERNIGHT HOURS. STILL A FAIR AMOUNT OF UNCERTAINTY IN LOCATION  
AND TIMING, SO HAVE LEANED ON VCTS FOR NOW. ALTHOUGH CONVECTION  
CANT BE 100% RULED OUT AT KRWL AND KLAR, CONFIDENCE IS LOW ENOUGH  
TO LEAVE OUT ANY TS MENTION. ALTHOUGH THERE IS INDICATION MAY  
LINGER AFTER 04Z, COVERAGE/INTENSITY WILL BE WANING, THUS  
MITIGATING IMPACT ON TERMINALS.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 252 AM MDT WED JUN 28 2017  
 
A DEEPLY MIXED BOUNDARY LAYER IS EXPECTED ONCE AGAIN THIS  
AFTERNOON. MODEL SOUNDING INDICATE MIXING HEIGHTS AS HIGH AS  
13,000 FT. WITH MODERATE LOWER TO MID LEVEL WINDS STILL PRESENT,  
EXPECT WINDS TO BE 20 TO 25 MPH WITH GUSTS TO 40 MPH AT TIMES  
ESPECIALLY OVER CARBON COUNTY. RH VALUES WILL FALL AS LOW AS 10 TO  
15 PERCENT WEST OF THE LARAMIE RANGE SO HAVE ISSUED A RED FLAG  
WARNING WHERE FUELS ARE READY. DRY THUNDERSTORMS ALSO A  
POSSIBILITY WITH WEAK CAPE ATOP THE DEEPLY MIXED BL. STRONG AND  
ERRATIC WINDS A POSSIBILITY WITH ANY CONVECTION. ELEVATED  
CONDITIONS ARE ALSO POSSIBLE OVER THE SOUTH LARAMIE RANGE AS WELL  
AS THE RAWLINS AREA THIS AFTERNOON. A COLD FRONT WILL MOVE ACROSS  
THE AREA ON THURSDAY BRINGING COOLER TEMPERATURES AND REDUCING THE  
FIRE WEATHER CONCERNS SOMEWHAT.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...RED FLAG WARNING FROM NOON TODAY TO 6 PM MDT THIS EVENING FOR  
WYZ306.  
 
NE...NONE.  
 

 
 

 
 
SHORT TERM...DEL  
LONG TERM...CAH  
AVIATION...CAH  
FIRE WEATHER...DEL  
 
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