FXUS65 KCYS 110037
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
537 PM MST THU DEC 10 2009

.UPDATE...LOCAL HIGH WIND WARNING FOR BORDEAUX AND ARLINGTON AREAS
ALLOWED TO EXPIRE AT 00Z. JLH

&&

.PREV DISCUSSION... /ISSUED 201 PM MST THU DEC 10 2009/ 

SHORT TERM...TONIGHT THROUGH SATURDAY...
STRONG WINDS WILL CONTINUE OVER AND NEAR THE MOUNTAINS THROUGH
SATURDAY.  IN GENERAL..WINDS OVER THAT AREA HAVE BEEN DIMINISHING
SLOWLY SINCE SUNRISE.  THE STRONGEST WINDS AS OF 2030Z WERE STILL
IN THE AREA FROM KARL TO KBRX WITH KARL REPORTING A GUST TO 50 MPH
AT 2010Z.  WILL KEEP THE PREVIOUSLY ISSUED HIGH WIND GOING FOR 
THOSE AREAS UNTIL 00Z.  WINDS WILL BE NEAR WARNING CRITERIA OVER 
AND NEAR THE MOUNTAINS AT TIMES THROUGH 00Z SUNDAY.  THE 700 MB
MODEL FORECAST WINDS ACTUALLY DIMINISH TO 30 TO 35 KNOTS OVER THE 
CWA STARTING ON FRIDAY.  HOWEVER...THE LOW LEVEL HEIGHT DIFFERENCE
ACROSS THE CWA WOULD SUGGEST STRONGER WINDS WITH THE DIFFERENCES
PEAKING ON SATURDAY.  THOSE STRONG WINDS WILL PRODUCE AREAS OF 
BLOWING AND DRIFTING SNOW...ESPECIALLY THROUGH TONIGHT.  WILL ALSO
MENTION BLOWING SNOW THROUGH SUNSET OVER THE PANHANDLE WHERE WINDS
HAVE BEEN GUSTING OVER 30 MPH.  

THE FLOW ALOFT BACKS THROUGH FRIDAY NIGHT AND HEIGHTS ALOFT RISE.
THIS IS IN ADVANCE OF A SHORTWAVE TROUGH CURRENTLY OFF THE 
CALIFORNIA COAST.  TEMPERATURES OVER THE CWA WILL CONTINUE TO 
WARM THROUGH SATURDAY AS 700 MB TEMPERATURES WARM TO -4C TO -6C
LATE FRIDAY NIGHT AND SATURDAY.  THOSE TEMPERATURES AND DOWNSLOPE
WINDS WILL RESULT IN HIGHS AT OR ABOVE NORMAL BY SATURDAY.  THE 
PREVIOUSLY MENTIONED SHORTWAVE TROUGH WILL MOVE ACROSS THE CENTRAL
ROCKIES FRIDAY NIGHT AND SATURDAY MORNING.  THAT FEATURE WILL
SPREAD CLOUDS OVER THE CWA AND SNOW MAINLY OVER THE SNOWY RANGE.
12Z BUFKIT RAOBS SUGGEST 2 TO 4 INCHES OF NEW SNOW ON THE WEST
FACING SLOPES OF THE SNOWY RANGE.  HAVE INCREASED POPS OVER AND
NEAR THE SNOWY RANGE FRIDAY NIGHT/SATURDAY AS WELL AS SNOW AMOUNTS.

LONG TERM...SATURDAY NIGHT THROUGH THURSDAY
THE GFS AND ECMWF HAVE SIMILAR IDEAS ABOUT THE FEATURES IN THE LONG 
TERM.  THE GFS IS MORE AMPLIFIED WITH THE UPPER RIDGE OVER THE WEST 
AT THE END OF THE PERIOD...WHEREAS THE ECMWF IS MORE PROGRESSIVE IN 
MOVING THE FEATURES ALONG.  TRIED TO GO WITH A COMPROMISE BETWEEN 
THE TWO MODELS...WITH TIMING CLOSER TO THE GFS.  ZONAL FLOW WILL BE 
OVER THE CWA SAT NIGHT WITH SOME SNOW SHOWERS OVER THE SOUTHERN HALF 
OF CARBON COUNTY.  A SHORT WAVE WILL MOVE ACROSS THE FORECAST AREA 
SUN WITH A SURFACE LOW MOVING INTO NORTHERN WY AT THIS TIME.  LIGHT 
SNOW WILL OCCUR ACROSS MUCH OF THE AREA...BUT SNOW AMOUNTS DO NOT 
LOOK SIGNIFICANT OUTSIDE THE MOUNTAINS.  HOWEVER...THE MOUNTAINS MAY 
NEED WINTER WEATHER HIGHLIGHTS SUN INTO SUN NIGHT.  COLDER 
TEMPERATURES WILL OCCUR MON AS A COLD FRONT MOVES SOUTH.  THIS SURGE 
OF COLD AIR WILL AFFECT AREAS MAINLY EAST OF THE LARAMIE RANGE WITH 
WINDS SHIFTING TO THE N TO NE BEHIND THE FRONT.  WEST WINDS SHOULD 
PREVAIL WEST OF THE LARAMIE RANGE.  LIGHT SNOW WILL OCCUR BEHIND THE 
COLD FRONT AS IT MOVES SOUTH...THEREFORE THE LIGHT SNOW WILL SPREAD 
SOUTH ACROSS THE AREA AS THE DAY WEARS ON.  ONCE AGAIN...SNOW 
AMOUNTS DO NOT LOOK SIGNIFICANT.  THE UPPER FLOW WILL BECOME NW MON 
NIGHT AS THE SHORT WAVE MOVES EAST AND THE UPPER RIDGE ALONG THE 
WEST COAST MOVES INLAND.  ON TUES...TEMPS WILL MODERATE A BIT AS THE 
FRONTAL BOUNDARY BEGINS TO MOVE BACK TO THE EAST.  THE UPPER FLOW 
WILL FLATTEN DURING THE AFTERNOON AS ANOTHER SHORT WAVE RIPPLE MOVES 
THROUGH THE FLOW.  A SURFACE LEE TROUGH WILL THEN SET UP TUES NIGHT 
AND NW FLOW WILL RETURN ALOFT AS THE UPPER RIDGE REBUILDS OVER THE 
WESTERN U.S.  THIS PATTERN WILL CONTINUE THROUGH WED...AND THE 
SOUTHERN MOUNTAINS WILL GET SOME OROGRAPHIC INDUCED SNOW.  THURSDAY 
LOOKS REALLY MILD COMPARED TO TEMPS OF LATE AS THE SURFACE LEE 
TROUGH STRENGTHENS LEADING TO MODERATE TO STRONG DOWNSLOPE WINDS.  
HIGH TEMPERATURES WILL BE AROUND NORMAL SUN...10 TO 12 DEGREES 
BELOW NORMAL MON...AROUND NORMAL FOR TUES AND WED...AND 5 DEGREES 
ABOVE NORMAL FOR THURS.

AVIATION...
VFR CONDITIONS WILL PREVAIL OVER MUCH OF THE CWA THROUGH SATURDAY.  
WEST WINDS WILL GUST TO AS HIGH AS 45 KNOTS OVER AND NEAR THE 
MOUNTAINS THROUGH SATURDAY AND WILL PRODUCE AREAS OF BLOWING SNOW...
ESPECIALLY TONIGHT. FAST NORTHWEST WIND FLOW ALOFT WILL STAY OVER
THE CWA THROUGH FRIDAY AND WILL CONTINUE TO PRODUCE MOUNTAIN WAVES
TO THE LEE OF THE SNOWY RANGE AND ALSO LARAMIE PEAK. SNOWY RANGE
WILL BECOME OBSCURED FRIDAY NIGHT AND CONTINUE THAT WAY SATURDAY AS
A SHORTWAVE TROUGH MOVES THROUGH THE CENTRAL ROCKIES. CLOUDS WILL
ALSO INCREASE AND LOWER OVER THE REST OF THE CWA FRIDAY NIGHT AND
SATURDAY MORNING WITH PERHAPS BRIEF MVFR CEILINGS AND VISIBILITIES
IN LIGHT SNOW AT KRWL AND KSAA.

FIRE WEATHER...
WITH THE COLD CONDITIONS AND RECENT SNOW COVER...FIRE WEATHER 
CONCERNS WILL BE MINIMAL OVER THE CWA THROUGH SATURDAY. WEST WINDS 
WILL BE STRONG OVER AND NEAR THE SNOWY AND LARAMIE RANGES THROUGH
SATURDAY WITH GUSTS TO 50 MPH POSSIBLE.  TEMPERATURES WILL MODERATE 
AND RETURN TO AT OR ABOVE NORMAL BY SATURDAY.  MINIMUM RELATIVE
HUMIDITY VALUES WILL BE BETWEEN 25 AND 35 PERCENT TO THE EAST OF THE
LARAMIE RANGE SATURDAY.   

&&

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

&&

$$

SHORT TERM/AVIATION...WEILAND
LONG TERM...KMD