FXUS65 KCYS 031004
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
305 AM MST THU DEC 3 2009

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT...

TODAY...PRIMARY CHALLENGE IS TEMPERATURES. BOTH 850 MB AND 700 MB 
PROGGED TEMPERATURES EVEN COOLER AT 5 PM TODAY THAN THOSE THAT 
OCCURRED WEDNESDAY. 700 MB TEMPERATURES PROGGED TO BE -20 TO -22 
CELSIUS AT 5 PM TODAY...1-2 DEGREES COLDER THAN SAME TIME YESTERDAY. 
PLUS...WITH MORE CLOUD COVER TODAY THAN YESTERDAY...EXPECT HIGH 
TEMPERATURES TO BE COLDER THAN YESTERDAY. THUS...THE COLDER GFS MOS 
HIGHS ARE MORE IN THE BALLPARK THAN WARMER NAM MOS WITH SOME MINOR 
TWEAKING. RECORD LOW MAXIMUM TEMPERATURES LOOK LIKELY AT CHEYENNE 
/16 IN 1873/...LARAMIE /18 IN 1978/...RAWLINS /18 IN 1978/. WEAK 
SHORTWAVE TROUGH ROTATING ACROSS OUR COUNTIES ALONG WITH WEAK 
500-300 MB AND 700-500 MB QUASIGEOSTROPHIC LIFT WILL PRODUCE 
ISOLATED SNOW SHOWERS ACROSS OUR NORTHERN COUNTIES AND OVER THE 
SNOWY RANGE AND SOUTHERN LARAMIE RANGE.

TONIGHT...BOTH THE NAM AND GFS SHOW DECREASING CLOUD COVER ALONG 
WITH DEVELOPING SURFACE LEE TROUGHING AS ARCTIC AIR RETREATS EAST IN 
ADVANCE OF NEXT SHORTWAVE TROUGH. WITH SNOWPACK AND CLEARING 
SKIES...EXPECT LOW TEMPERATURES TO BE ACHIEVED AROUND MIDNIGHT WITH 
STEADY OR SLOWLY WARMING TEMPERATURES THEREAFTER AS WEST WINDS 
INCREASE. WITH COLD TEMPERATURES AT LATE AFTERNOON...GFS/NAM MOS LOW 
TEMPERATURES LOOK TOO WARM AND HAVE UNDERCUT...ESPECIALLY AT LARAMIE 
WHERE COLD AIR WILL REMAIN TRAPPED IN THE LARAMIE VALLEY.

FRIDAY...NOT NEARLY AS COLD AS 700 MB TEMPERATURES RISE TO NEAR -8 
CELSIUS AND 1000-500 MB THICKNESSES CLIMB TO 5340 METERS BY 5 PM 
FRIDAY. HIGH TEMPERATURES IN THE 20S TO LOWER 30S WITH WARMING 
DOWNSLOPE WEST WINDS AIDING WARMUP.

FRIDAY NIGHT...COMBINATION OF INCREASING MID CLOUDS AHEAD OF 
APPROACHING SHORTWAVE TROUGH AND DECENT LOW LEVEL MIXING WILL KEEP 
LOW TEMPERATURES FROM BOTTOMING OUT AS MUCH AS TONIGHT. LOCALLY 
WARMER MINIMUM TEMPERATURES TO THE LEE OF THE LARAMIE RANGE DUE TO 
DECENT LOW LEVEL WINDS AND MIXING.

.LONG TERM...SATURDAY THROUGH WEDNESDAY...
RATHER DIFFICULT FORECAST FOR THIS PERIOD WITH COMPLICATED 
MULTI-STREAM PATTERN FORECAST OVER THE COUNTRY.  WILL BASICALLY 
AVERAGE OUT MODELS SOLUTIONS AND FAVOR WARMEST DAY OF THIS PERIOD 
BEING ON SATURDAY AS CWA EXPECTED TO BE IN BETWEEN SYSTEMS.  
TEMPERATURES WILL STILL BE A BIT ON THE COOL SIDE HOWEVER WITH HIGHS 
IN THE 20S TO MID 30S.  BOTTOM DROPS OUT AGAIN AS NEXT STRONG COLD 
FRONT THEN EXPECTED TO PUSH ACROSS BY LATE SATURDAY AS NEXT UPPER 
SYSTEM DROPS INTO THE PACIFIC NW.  COLD SFC AIRMASS WILL SETTLE OVER 
THE CWA INTO THE MID PART OF NEXT WEEK MAINTAINING WELL BELOW 
AVERAGE TEMPERATURES.  A SHOT OF LIGHT SNOW SHOULD MOVE OVER MUCH 
OF THE CWA BEHIND THIS NEXT FRONT THEN WILL FAVOR BULK OF PCPN 
PUSHING SOUTH OVER COLORADO WHERE MAIN UPPER FLOW SHOULD RESIDE 
THOUGH MTN SNOW SHOWERS WILL PERSIST OVER SRN WY.   

&&

.AVIATION...
MAINLY VFR CONDITIONS EXPECTED THROUGH FRIDAY THOUGH LOCALIZED MVFR 
CONDITIONS DUE TO LOWERED CIGS EXPECTED ALONG WITH SOME MTN 
OBSCURATIONS AS POCKETS OF ENHANCED MOISTURE MOVE ACROSS IN 
NORTHERLY UPPER FLOW.   

&&

.FIRE WEATHER...NO FIRE WEATHER ISSUES THROUGH FRIDAY NIGHT.

&&

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

&&

$$

SHORT TERM/AVIATION...RUBIN
LONG TERM...RE