FXUS65 KCYS 112201
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
301 PM MST FRI DEC 11 2009

.SHORT TERM...TONIGHT THROUGH SUNDAY...CURRENT OBS SHOW MOSTLY
CLEAR SKIES OVER THE REGION THIS AFTERNOON WITH INCREASING CLOUDS
FURTHER WEST OVER SOUTHEAST WYOMING AND WRN COLORADO. THESE CLOUDS
ARE ASSOCIATED WITH A WEAK UPPER LEVEL DISTURBANCE PUSHING ACROSS
THE GREAT BASIN REGION TONIGHT. MODELS IN GOOD AGREEMENT...SHOWING
THIS DISTURBANCE MOVING INTO WYOMING AND THE SRN MOUNTAINS BY LATE
TONIGHT AND SATURDAY MORNING. WITH WEST TO SOUTHWEST FLOW OVER THE
AREA...EXPECT TEMPS TO CONTINUE TO WARM...WITH HIGHS IN THE 40S
POSSIBLE TOMORROW AFTERNOON EAST OF THE LARAMIE RANGE. SOME
MOUNTAIN SNOW SHOWERS ARE EXPECTED ACROSS THE SIERRA MADRE AND
SNOWY RANGES WITH UPSLOPE FLOW...MAINLY THE WEST FACING SLOPES.
EXPECT AN INCH OR TWO OF SNOW ABOVE 9000 FEET ACROSS CARBON AND
ALBANY COUNTIES WITH THIS INITIAL DISTURBANCE THROUGH SATURDAY
EVENING. BY EARLY SUNDAY...MODELS SHOW THE MAIN UPPER LEVEL LOW
AND ASSOCIATED PACIFIC COLD FRONT PUSHING INTO THE WEST COAST AND
THEN INTO WYOMING BY SUNDAY AFTERNOON...RESULTING IN INCREASING
PRECIP AND MORE WINDY CONDITIONS OVER PORTIONS OF WYOMING AND WRN
NEBRASKA. ALL MODELS SHOW THIS TROUGH MOVING ACROSS THE AREA QUICK WITH
A SURFACE LOW DEVELOPING OVER WRN WYOMING AND TRANSLATING EASTWARD
OVER THE NORTH PLATTE RIVER VALLEY. EXPECT THE BEST CHANCE FOR
SNOW TO BE NORTH AND WEST OF THIS AREA OF SURFACE CONVERGENCE.
INCREASED POP BETWEEN 30 TO 50 PCT ALONG AND WEST OF THE LARAMIE
RANGE AND THE HIGH PLAINS OF EAST CNTRL WYOMING WITH POP NEAR 80
PCT IN THE MOUNTAINS. EXPECT ANOTHER 2 TO 5 INCHES OF SNOW IN THE
MOUNTAINS SUNDAY WITH LITTLE ACCUMULATION IN THE VALLEYS. THE ONLY
MINOR CONCERN IS THE ECMWF AND GFS ARE SHOWING A DEEPER TROUGH TO
THE NORTH IN CANADA...WITH AN ARCTIC COLD FRONT SLOWLY PUSHING
SOUTH ALONG THE FRONT RANGE OF MONTANA AND NORTHEAST WYOMING LATE
SUNDAY...RESULTING IN ADDED FRONTOGENESIS OVER THE HIGH
PLAINS...LLVL UPSLOPE EASTERLY FLOW...AND SIGNIFICANTLY COLDER
TEMPS OVER THE NRN NEBRASKA PANHANDLE AND CONVERSE AND NIOBRARA
COUNTIES IN WYOMING. KEPT LIGHT PRECIP IN THE FORECAST FOR
NOW...BUT DID LOWER MAX TEMPS ON SUNDAY INTO THE 20S AND LOWER 30S
AS THIS ARCTIC AIR MASS WILL LIKELY BE CLOSE TO THE HIGH PLAINS
LATER ON SUNDAY. OTHERWISE...WINDY CONDITIONS WILL CONTINUE AT
TIMES THROUGH THE WEEKEND...MAINLY IN THE WIND PRONE AREAS ALONG
I25 AND I80 AS A LEE-SIDE TROUGH REMAINS OVER THE HIGH PLAINS WITH
700MB WINDS AROUND 50KTS INTO SUNDAY MORNING. INCREASED WINDS
ALONG AND WEST OF THE LARAMIE RANGE WITH ISOLATED GUSTS UP TO 65
MPH POSSIBLE. MAY NEED HIGH WIND HIGHLIGHTS IN A FEW
LOCATIONS...BUT HIGHER WIND GUSTS LOOK TO BE VERY ISOLATED.

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...A SHORTWAVE TROUGH WILL 
MOVE ACROSS THE CENTRAL ROCKIES SUNDAY NIGHT. AS THE FEATURE
MOVES EAST IT WILL HELP TO DRAW DOWN A SHALLOW SURFACE FRONT TO
THE EAST OF THE LARAMIE RANGE. THE SHORTWAVE TROUGH WILL PRODUCE
SNOW MAINLY OVER AND AND WEST OF THE SNOWY RANGE SUNDAY NIGHT. FOR
NOW WILL KEEP SEVERAL INCHES OF SNOW FOR THAT AREA DURING THAT
TIME. THROUGH THE REST OF THE WEEK...HEIGHTS ALOFT RISE SLOWLY
OVER THE ROCKIES AND BY NEXT FRIDAY A LARGE AMPLITUDE RIDGE WILL
BE OVER THE WESTERN PART OF THE NATION PER BOTH THE ECMWF AND GFS.
AS THE HEIGHTS ALOFT RISE...OROGRAPHIC SNOW WILL TAPER OFF AND END
OVER THE SNOWY RANGE THROUGH TUESDAY.

THE NAM...SREF AND ECMWF ARE FASTER IN THE SOUTHWARD MOVEMENT OF THE 
INITIAL FRONT THAN THE GFS.  THOSE MODELS MOVE THE FRONT TO ALONG 
THE LARAMIE RANGE BY 00Z MONDAY WHILE THE GFS IS BETWEEN 06Z AND 
12Z.  FOR NOW WILL LEAN TOWARD THE FASTER MODELS FOR THIS FORECAST. 
LIGHT SNOW OR FLURRIES SHOULD BE OVER THE NORTH PART OF THE CWA
SUNDAY NIGHT WHERE THE COLD AIR IS DEEPER.  THE SURFACE BOUNDARY 
THEN MOVES SLOWLY EAST FROM THE LARAMIE RANGE THROUGH MONDAY.  A 
SHORTWAVE TROUGH WILL MOVE OVER THE NORTHERN PLAINS MONDAY NIGHT AND 
THEN CONTINUES QUICKLY SOUTHEAST.  THAT FEATURE WILL PUSH A 
REINFORCING SURGE OF COLD AIR OVER THE EAST PART OF THE CWA MONDAY 
NIGHT.  LOWER CLOUDS AND MAINLY FLURRIES SHOULD DEVELOP TO THE EAST 
OF THE BOUNDARY MONDAY NIGHT AND TUESDAY MORNING.  THAT BOUNDARY 
THEN MOVES SLOWLY EAST AS A SURFACE LOW PRESSURE TROUGH INTO LATE 
NEXT WEEK.  ANOTHER SHALLOW SURGE OF COLD AIR MOVE OVER THE EAST 
PART OF THE CWA BY THE MODELS NEXT FRIDAY.  BEHIND THE BOUNDARIES 
WILL BE COLD TEMPERATURES AND EASTERLY WINDS...WHILE TO THE WEST OF 
THE BOUNDARIES WILL BE GUSTY WESTERLY WINDS AND WARMER READINGS.  
TEMPERATURES OVER THE ENTIRE CWA WILL BE ABOVE NORMAL WEDNESDAY AND 
THURSDAY.  

&&

.AVIATION...VFR CONDITIONS EXPECTED THROUGH TONIGHT. CLOUDS
WILL GRADUALLY INCREASE LATE TONIGHT AND EARLY SATURDAY
MORNING FROM WEST TO EAST...ESPECIALLY IN CARBON AND ALBANY
COUNTIES. THERE IS A 10 PCT CHANCE OF CIGS AROUND 3K FEET AND ISOLD
SNOW SHOWERS BY 18Z SATURDAY MORNING AROUND KRWL AND KLAR AS A
WEAK DISTURBANCE PUSHES INTO THE AREA. 
&&

.FIRE WEATHER...WITH COOL TEMPS AND MOUNTAIN PRECIP THIS WEEKEND...NO
FIRE WEATHER CONCERNS ANTICIPATED INTO EARLY NEXT WEEK. STRONG
WEST TO SOUTHWEST WINDS BETWEEN 20 TO 40 MPH ARE EXPECTED THROUGH
THIS WEEKEND WITH GUSTS POSSIBLY AS HIGH AS 65 IN A FEW AREAS. 
&&

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

&&

$$

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