FXUS65 KCYS 092131
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
231 PM MST WED DEC 9 2009

.SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT...STRONG WINDS AND
BLOWING SNOW WILL BE COMMON OVER MUCH OF THE WYOMING PART OF THE
CWA FOR THIS PORTION OF THE FORECAST. THE COLD TEMPERATURES WILL
SLOWLY MODERATE THROUGH 12Z FRIDAY BUT WILL STILL REMAIN WELL
BELOW NORMAL. LOWS TONIGHT IN MOST PLACES WILL NOT BE AS COLD AS
LAST NIGHT...BUT ALONG WITH THE WINDS...WIND CHILL VALUES WILL
AGAIN LOWER TO WIND CHILL ADVISORY CRITERIA. WILL GO AHEAD AND
ISSUE A WIND CHILL ADVISORY OVER MUCH OF THE CWA FROM 02Z TO 16Z.
THE MAIN CONCERN WILL STILL BE THE WINDS AND BLOWING SNOW OVER
SOUTHEAST WYOMING THROUGH THURSDAY NIGHT. SOME ROADS...INCLUDING
INTERSTATE 80 HAVE BEEN CLOSED DUE TO THE BLOWING SNOW AS OF EARLY
THIS AFTERNOON. CONSIDERED AGAIN ISSUING A BLIZZARD WARNING...BUT
FOR NOW WILL STICK WITH THE GOING WINTER WEATHER ADVISORY FOR
BLOWING SNOW AND THE HIGH WIND WARNING THROUGH 21Z THURSDAY. WINDS
HAVE TOUCHED HIGH WIND CRITERIA AT TIMES SINCE THE MID MORNING AT
KBRX...KVDW AND KARL. WINDS WILL INCREASE OVER SOUTHEAST WYOMING
THIS EVENING AND CONTINUE FOR MUCH OF THURSDAY. WINDS SHOULD BE
THE STRONGEST OVER AND NEAR THE MOUNTAINS AND AFTER THE SHORTWAVE
TROUGH MOVES SOUTHEAST OF THE CWA EARLY TONIGHT. THE LOW LEVEL
HEIGHT DIFFERENCES ACROSS THE CWA DECREASE SOME BY 00Z FRIDAY AND
THEN INCREASE AGAIN THURSDAY NIGHT. THE NORTHWEST FLOW ALOFT IS
VERY FAST WITH A 110 KNOT JET BISECTING THE CWA THROUGH THURSDAY
NIGHT. AT 700 MB THE MODELS HAVE 40 TO 45 KNOTS OVER THE AREA
THROUGH THURSDAY NIGHT. THE PREVIOUSLY MENTIONED SHORTWAVE TROUGH
WILL PRODUCE LIGHT SNOW OVER THE SNOWY RANGE THROUGH TONIGHT WITH
SEVERAL INCHES OF NEW SNOW LIKELY.

.LONG TERM...FRIDAY THROUGH NEXT WEDNESDAY...MODELS IN GOOD 
AGREEMENT LATE THIS WEEK AND INTO THIS WEEKEND...SHOWING MAINLY 
ZONAL FLOW AND WINDY CONDITIONS THROUGH THE PERIOD AS THE ARCTIC 
AIRMASS...CURRENTLY OVER THE ERN TWO THIRDS OF THE UNITED STATES
AND CANADA...SHIFTS NORTHEASTWARD. A PACIFIC UPPER LEVEL TROUGH
IS EXPECTED TO PUSH INTO THE INTERMOUNTAIN WEST SATURDAY
NIGHT...RESULTING IN SOME MOUNTAIN SNOW SATURDAY AND SUNDAY. CAN
NOT RULE OUT SOME LIGHT SNOW IN THE LOWER ELEVATIONS OF WYOMING
AND NEBRASKA PANHANDLE AS WELL WITH THE LEFT EXIT REGION OF A
STRONG JET OVER THE AREA...BUT EXPECT ACCUMULATING SNOWFALL TO 
REMAIN IN THE MOUNTAINS WHERE 2 TO 5 INCHES ARE POSSIBLE THROUGH
SUNDAY. THE MAIN IMPACT THIS PERIOD WILL BE STRONG WEST TO
SOUTHWEST WINDS OVER THE HIGHER ELEVATIONS OF WYOMING ALONG AND
WEST OF THE LARAMIE RANGE...WITH HIGH WIND CRITERIA POSSIBLE
FRIDAY NIGHT AS A LEE-SIDE TROUGH DEVELOPS OVER THE HIGH PLAINS
AND 700MB WINDS APPROACH 60 KTS. OTHERWISE...CONTINUED THE SLIGHT
WARMING TREND INTO THE WEEKEND WITH TEMPS INCREASING TO NEAR
NORMAL BY SATURDAY...ESPECIALLY OVER THE HIGH PLAINS. TEMPS ARE
EXPECTED TO REMAIN BELOW NORMAL IN THE VALLEYS WEST OF THE LARAMIE
RANGE WITH A WEAK VALLEY TEMP INVERSION EXPECTED INTO SATURDAY.
INCREASED POP...ESPECIALLY OVER THE MOUNTAINS WITH UPSLOPE FLOW
EXPECTED LATE SATURDAY AND SUNDAY.

FOR EARLY NEXT WEEK...MODEL SOLUTIONS DIVERGE AS AN ARCTIC COLD 
FRONT MOVES ACROSS WESTERN CANADA AND ALONG THE U.S. BORDER. ECMWF 
IS THE WARMEST SOLUTION...SHOWING THE ARCTIC AIRMASS REMAINING WELL 
NORTH OF THE AREA AS IT QUICKLY PUSHES EAST.  HOWEVER...THE GEM AND 
GFS SHOW THE ARCTIC COLD FRONT AND ASSOCIATED UPPER LEVEL TROUGH 
DIGGING SOUTHEAST INTO WYOMING MONDAY AND MONDAY NIGHT...WITH 700MB 
TEMPS LOWERING TO BELOW -20C AND SOME LIGHT SNOW SHOWERS. GFS 
ENSEMBLE FORECASTS IN GOOD AGREEMENT WITH ONLY ONE PERTURBATION 
SIMILAR TO THE ECMWF. KEPT SOME SNOW SHOWERS IN THE MOUNTAINS 
THROUGH WEDNESDAY. ALSO LOWERED MAX AND MIN TEMPS EARLY NEXT 
WEEK...MAINLY OVER THE NEBRASKA PANHANDLE WITH HIGHS IN THE 20S AND 
30S AND LOWS IN THE SINGLE DIGITS AND TEENS. ALTHOUGH IF THE GEM 
VERIFIES...MAY NEED TO LOWER TEMPS SIGNIFICANTLY ACROSS THE ENTIRE 
AREA. KEPT BREEZY TO WINDY CONDITIONS OVER THE HIGHER ELEVATIONS OF 
WYOMING AND THE HIGH PLAINS WITH A STRONG LLVL PRESSURE GRADIENT 
EXPECTED.
&&

.AVIATION...THE SNOWY RANGE WILL BE OBSCURED THROUGH THURSDAY 
MORNING.  OTHERWISE...VFR CONDITIONS WILL BE COMMON OVER THE CWA
THROUGH 12Z FRIDAY.  STRONG WESTERLY SURFACE WINDS WILL GUST AS 
HIGH AS 50 KNOTS OVER AND NEAR THE MOUNTAINS THROUGH THURSDAY NIGHT
AND WILL PRODUCE BLOWING SNOW.  THE BLOWING SNOW WILL REDUCE 
VISIBILITIES FREQUENTLY TO MVFR VALUES IN BLOWING SNOW AT KRWL...
KLAR AND KEAN WITH BRIEF IFR VISIBILITIES.  THE FAST NORTHWEST WIND
FLOW WILL BE OVER THE CWA THROUGH THURSDAY NIGHT AND WILL CONTINUE
TO PRODUCE MOUNTAIN WAVES TO THE LEE OF THE SNOWY RANGE AND LARAMIE
PEAK. 
&&

.FIRE WEATHER...WITH THE COLD CONDITIONS AND SNOW COVER...FIRE 
WEATHER CONCERNS WILL BE MINIMAL OVER THE CWA THROUGH FRIDAY. 
WESTERLY SURFACE WINDS WILL BE STRONG OVER MUCH OF SOUTHEAST WYOMING
THROUGH FRIDAY WITH SOME GUSTS BETWEEN 50 AND 60 MPH...ESPECIALLY
OVER AND NEAR THE MOUNTAINS.  TEMPERATURES WILL CONTINUE TO MODERATE
AND WILL RETURN TO AT OR ABOVE NORMAL OVER THE WEEKEND.  
&&

.CYS WATCHES/WARNINGS/ADVISORIES...

WY...WINTER WEATHER ADVISORY UNTIL 2 PM THURSDAY FOR WYZ103-WYZ104-
     WYZ105-WYZ106-WYZ109-WYZ110-WYZ111-WYZ112-WYZ113-WYZ114-
     WYZ115-WYZ116-WYZ117.

     HIGH WIND WARNING UNTIL 2 PM THURSDAY FOR WYZ106-WYZ117.
     WIND CHILL ADVISORY FROM 7 PM WEDNESDAY TO 9 AM THURSDAY FOR 
     WYZ101-WYZ102-WYZ103-WYZ104-WYZ105-WYZ106-WYZ109-WYZ110-
     WYZ111-WYZ112-WYZ113-WYZ114-WYZ115-WYZ116-WYZ117.

     HIGH WIND WARNING UNTIL 2 PM THURSDAY FOR WYZ110-WYZ116.
     WINTER WEATHER ADVISORY UNTIL 5 PM WEDNESDAY FOR WYZ107-WYZ118-
     WYZ119.

NE...WIND CHILL ADVISORY FROM 7 PM WEDNESDAY TO 9 AM THURSDAY FOR 
     NEZ002-NEZ003-NEZ019-NEZ020-NEZ021-NEZ054-NEZ055-NEZ095-
     NEZ096.

&&

$$

SHORT TERM/AVIATION...WEILAND
LONG TERM...TJT