827  
FXUS65 KCYS 080303  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
803 PM MST WED DEC 7 2016  
   
UPDATE
 
 
ISSUED AT 758 PM MST WED DEC 7 2016  
 
7 PM MST OBSERVATIONS INDICATED NUMEROUS SITES WITH WIND CHILLS AT  
OR BELOW -20F ALONG THE I80 CORRIDOR BETWEEN LAR AND IBM. CHEYENNE  
HAS FALLEN TO -26F. TEMPERATURES SHOULD CONTINUE TO FALL WITH WIND  
SPEEDS REMAINING AROUND 5 TO 10 MPH. IN A RECENT UPDATE, ADDED THE  
REMAINING I80 CORRIDOR ZONES TO THE WIND CHILL ADVISORY. WILL NEED  
TO MONITOR FOR POSSIBLE UPGRADES TO A WARNING, PARTICULARLY ACROSS  
THE I80 SUMMIT, BUT WOULD NOT RULE OUT AREAS FURTHER EAST.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH FRIDAY NIGHT)  
ISSUED AT 230 PM MST WED DEC 7 2016  
 
LIGHT SNOW/FLURRIES PRETTY MUCH GONE NOW AND SKIES ON THE WAY TO  
CLEARING. THIS ALONG WITH LIGHT WINDS AND SNOW COVER WILL BE  
OPTIMAL FOR A VERY COLD NIGHT ACROSS THE CWA. THERE WILL NOT BE  
MUCH IN THE WAY OF A BREEZE BUT WITH TEMPERATURES FALLING BELOW  
ZERO ACROSS THE CWA VERY LOW TO DANGEROUS WIND CHILLS ARE  
EXPECTED...LOWEST OVER THE LARAMIE VALLEY. HAVE POSTED A WIND  
CHILL WARNING FOR THE LARAMIE VALLEY AND SURROUNDING AREAS WITH A  
WIND CHILL ADVY FOR MUCH OF THE REST OF THE CWA. FAR WESTERN  
AREAS AND THAT AREA FROM ABOUT CHEYENNE TO KIMBALL MARGINAL AND  
BRIEF SO HAVE OPTED TO OMIT THAT AREA FOR THE TIME BEING.  
 
DRY AND A LITTLE WARMER ACROSS THE CWA THURSDAY BUT STILL CHILLY  
WITH THE COLD SURFACE HIGH ANCHORED OVER THE PLAINS. TEMPERATURES  
THEN BECOME TRICKY THURSDAY NIGHT AS THE COLD SURFACE AIRMASS WILL  
RETREAT EASTWARD THUS LOWS ACROSS MOST OF SOUTHEAST WY SHOULD  
OCCUR THURSDAY EVENING WITH TEMPERATURES THEN RISING OVERNIGHT AS  
WARMER DOWNSLOPE FLOW OCCURS. FRIDAY MUCH WARMER ACROSS SOUTHEAST  
WYOMING INTO THE SOUTHWEST PART OF THE PANHANDLE BUT THE COLDER  
AIR MAY HOLD NORTH OF A LINE FROM EAST OF DOUGLAS TO ALLIANCE.  
OTHERWISE SHOULD SEE AN UPTICK IN SNOW SHOWERS OVER THE WESTERN  
MTNS FRIDAY AS MOISTURE IN WESTERLY UPPER FLOW RIDES UP THE FACING  
SLOPES. THIS WILL PERSIST THROUGH SATURDAY...POSSIBLY MOVING OUT  
OVER THE PLAINS AS AN UPPER SHORTWAVE MOVES ACROSS THE REGION.  
   
LONG TERM
 
(SATURDAY THROUGH WEDNESDAY)  
ISSUED AT 230 PM MST WED DEC 7 2016  
 
THE 12Z GFS IS AROUND 18-24 HRS FASTER WITH THE SHORTWAVE TROUGH  
PASSAGE ON SATURDAY, BRINGING IT THROUGH DURING THE DAY. THE 12Z  
ECMWF SHOWS THE TROUGH AXIS MOVING OVERHEAD BY MIDDAY SUNDAY. IT  
APPEARS THAT THE EURO IS THE OUTLIER AS BOTH THE NAM AND CANADIAN  
MODELS ARE SIMILAR TO THE GFS. THUS, WOULD EXPECT BREEZY TO WINDY  
CONDITIONS FROM SATURDAY INTO SUNDAY MORNING OVER MUCH OF THE REGION  
WITH A GOOD CHANCE OF OROGRAPHIC SNOWS ACROSS THE SIERRA MADRE AND  
SNOWY RANGES. MUCH OF THE SNOW SHOULD END BY LATE SUNDAY OVER THE  
MTNS WITH HIGHS IN THE 30S ACROSS LOWER ELEVATIONS. THERE IS QUITE  
A BIT OF SPREAD AS WE HEAD INTO EARLY NEXT WEEK. NORTHWESTERLY FLOW  
ALOFT WILL BE IN PLACE, WITH THE CWA SUSCEPTIBLE TO FRONTS COMING IN  
FROM THE NORTHEAST. ANOTHER COLD INTRUSION COULD OCCUR BY TUESDAY,  
HOWEVER TEMPS ARE NOT EXPECTED TO BE AS COLD AS WITH THIS ARCTIC  
BLAST. PERIODS OF SNOW WILL OCCUR EARLY NEXT WEEK OVER THE MTNS  
WITH MOIST WEST TO NORTHWEST FLOW AND THE UPPER JET OVERHEAD.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)  
ISSUED AT 510 PM MST WED DEC 7 2016  
 
VFR CONDITIONS TONIGHT BENEATH MOSTLY CLEAR SKIES. WINDS SHOULD BE  
ON THE LIGHT SIDE.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 230 PM MST WED DEC 7 2016  
 
NO CONCERNS THROUGH THE WEEKEND WITH COLD TO COOL TEMPERATURES  
KEEPING CONDITIONS NON-CRITICAL.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...WIND CHILL ADVISORY UNTIL 9 AM MST THURSDAY FOR WYZ101-102-104-  
106>109-116>119.  
 
WIND CHILL WARNING UNTIL 9 AM MST THURSDAY FOR WYZ103-105-110-  
113>115.  
 
NE...WIND CHILL ADVISORY UNTIL 9 AM MST THURSDAY FOR NEZ002-003-  
019>021-054-055-095-096.  
 

 
 

 
 
UPDATE...CLH  
SHORT TERM...RE  
LONG TERM...ZF  
AVIATION...CLH  
FIRE WEATHER...RE  
 
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