FXUS65 KCYS 160443 AAA
AFDCYS

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHEYENNE WY
943 PM MST TUE DEC 15 2009

.UPDATE...
BASED ON OBSERVATIONS OVER THE PAST SEVERAL HOURS...HAVE DECIDED
TO GO AHEAD AND END THE HIGH WIND WARNING A BIT EARLIER THAN
ANTICIPATED. BREEZY WINDS OF 20 TO 30 MPH WITH GUSTS TO AROUND 50
MPH WILL STILL BE POSSIBLE TONIGHT AND ESPECIALLY AGAIN TOMORROW
AFTERNOON AHEAD OF THE APPROACHING COLD FRONT. TEMPERATURES
TONIGHT WILL CONTINUE TO BE A CHALLENGE...ESPECIALLY IN THE
NEBRASKA PANHANDLE...WITH THE LEE TROUGH EXPECTED TO SHIFT EAST
AS A WARM FRONT. THE COLD AIR REMAINS IN THE NORTH PLATTE RIVER
VALLEY LATE THIS EVENING...BUT MAY SCOUR OUT OVERNIGHT WITH
WARMING TEMPERATURES INTO THE 20S. THIS HAS ALREADY OCCURRED
TONIGHT IN THE CHADRON AREA WHERE THE COLDER AIRMASS WAS IN PLACE
MUCH OF TODAY. TEMPERATURES TOMORROW IN SOUTHEAST WYOMING WILL
PEAK OUT AT AROUND 10 DEGREES ABOVE NORMAL VALUES AS COMPRESSIONAL
WARMING USUALLY HELPS BUMP UP TEMPERATURES EVEN A BIT ABOVE
GUIDANCE VALUES IN A PRE-FRONTAL ENVIRONMENT.

&&

.LONG TERM...THURSDAY NIGHT THROUGH NEXT TUESDAY...
MODELS IN REASONABLE AGREEMENT INTO THE WEEKEND...BUT THEN
SOLUTIONS DIVERGE SIGNIFICANTLY LATE IN THE WEEKEND AND EARLY NEXT
WEEK. MODELS GENERALLY SHOW NORTH TO NORTHWEST FLOW FRIDAY AND
SATURDAY AS A SERIES OF WEAK PACIFIC TROUGHS QUICKLY PUSH ACROSS
THE NRN AND CNTRL ROCKIES AND INTO THE PLAINS. EXPECT TEMPERATURES
TO BE NEAR OR SLIGHTLY BELOW NORMAL FOR THIS TIME OF THE YEAR
GOING INTO THE WEEKEND WITH A CHC OF SNOW ACROSS THE AREA THURSDAY
NIGHT AND EARLY FRIDAY MORNING. SNOW ACCUMULATIONS APPEAR TO BE
MINIMAL AT THIS TIME WITH MANY AREAS OVER THE LOWER ELEVATION
RECEIVING ONLY SNOW FLURRIES AS A WEAK COLD FRONT MOVES ACROSS THE
AREA THURSDAY EVENING. BY SUNDAY...MODELS SHOW ANOTHER COLD FRONT
PUSHING SOUTHWARD OUT OF CANADA AS AN ARCTIC AIRMASS MOVES INTO
SRN CANADA AND THE NRN PLAINS. GFS IS THE FURTHEST WEST WITH THE
ARCTIC AIRMASS...SHOWING A DEEPER TROUGH DIGGING SOUTHEAST OVER
THE NRN ROCKIES WITH ANOTHER CHC OF SNOW AND MUCH COLDER TEMPS
ACROSS THE REGION. IN CONTRAST...OTHER MODELS INCLUDING THE GEM
AND ECMWF ARE SHOWING THIS AIRMASS FURTHER TO THE EAST WITH ONLY A
WEAK SHORTWAVE QUICKLY PUSHING ACROSS THE HIGH PLAINS. WITH THE
GFS THE OUTLIER...TRENDED TOWARDS THE GEM AND ECMWF WITH LOWER POP
AND TEMPS NEAR NORMAL IN WYOMING...WITH BELOW NORMAL TEMPS OVER
THE NEBRASKA PANHANDLE CLOSER TO THE ARCTIC AIRMASS.

BY EARLY NEXT WEEK...GFS SHOWS MAINLY WESTERLY FLOW AS ANOTHER
UPPER LEVEL TROUGH ESTABLISHES ITSELF OVER THE PACIFIC 
NORTHWEST...SLOWLY DRIFTING EASTWARD INTO TUESDAY. THE ECMWF
SHOWS THIS TROUGH MOVING EASTWARD MUCH SOONER COMPARED TO THE
GFS...MOVING INTO THE AREA BY LATE TUESDAY BRINGING COLDER TEMPS AND
SNOW. LOW CONFIDENCE WITH DAYS 6 AND 7...THEREFORE DID NOT MAKE
MANY CHANGES TO THE PREVIOUS FORECAST AND TRENDED POP TOWARDS
CLIMO WITH A CHC OF SNOW OVER THE MOUNTAINS ALONG AND WEST OF THE
LARAMIE RANGE. KEPT POP BELOW 15 PCT OVER THE HIGH PLAINS OF ERN
WYOMING AND THE NEBRASKA PANHANDLE WITH TEMPS SLIGHTLY BELOW
NORMAL. 

&&

.AVIATION...
BREEZY SOUTH TO SOUTHWEST WINDS WILL CONTINUE THROUGH THIS
EVENING...ESPECIALLY ALONG AND WEST OF THE LARAMIE RANGE NEAR KLAR
AND KRWL...AND THE BREEZY WINDS WILL CONTINUE AHEAD OF A COLD
FRONTAL PASSAGE WEDNESDAY EVENING. OTHERWISE...VFR CONDITIONS
ARE STILL EXPECTED INTO WEDNESDAY WITH INTERVALS OF MID TO HIGH
CLOUDS PUSHING ACROSS THE REGION.

&&

.FIRE WEATHER...
BREEZY WINDS WILL BE PRESENT ACROSS THE DISTRICT TONIGHT AND
WEDNESDAY WITH A COLD FRONT EXPECTED TO PASS FROM NORTHWEST TO
SOUTHEAST ACROSS THE AREA EARLY WEDNESDAY EVENING. THIS WILL
PRODUCE COOLER TEMPERATURES THURSDAY...THOUGH STILL A FEW DEGREES
ABOVE NORMAL. HIGHS WEDNESDAY IN SOUTHEAST WYOMING ARE EXPECTED
TO BE AROUND TEN DEGREES ABOVE NORMALS FOR MID-DECEMBER...BUT
CLOSER TO NORMAL CONDITIONS CAN BE EXPECTED IN THE NEBRASKA
PANHANDLE WHICH WILL BE CLOSER TO THE COLDER AIRMASS.

&&

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

&&

$$

SHORT TERM/FIRE WEATHER...CARPENTER 
LONG TERM...TJT
AVIATION...CYS