FXUS65 KCYS 030136
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
635 PM MST WED DEC 2 2009
.DISCUSSION...FLURRIES OVER EAST CENTRAL WYOMING AND THE NORTHERN
PANHANDLE HAVE HAD A HARD TIME SPREADING SOUTH SO FAR EARLY THIS
EVENING. A SHORTWAVE TROUGH CURRENTLY OVER NORTHEAST WYOMING WILL
MOVE SOUTH AND OVER MUCH OF THE CWA THROUGH THE REST OF TONIGHT.
THAT FEATURE SHOULD SPREAD CLOUDS AND SOME FLURRIES OVER THE REST OF
THE CWA AFTER 06Z. LOW TEMPERATURES WILL ALSO BE TRICKY TONIGHT
WITH THE INCREASE IN CLOUD COVER AND INITIAL CHILLY READINGS. KLAR
DROPPED DOWN TO -8 ALREADY BY 01Z AND KRWL WAS AT -1. LOWERED THE
MINIMUM TEMPERATURES FOR TONIGHT A BIT IN THE SOUTHWEST PART OF THE
CWA. FINALLY...SHALLOW FOG HAS FORMED OVER PORTIONS OF THE LARAMIE
VALLEY EARLY THIS EVENING WITH VISIBILITIES BELOW ONE MILE. IN A
RECENT FORECAST UPDATE MADE CHANGES DISCUSSED ABOVE.
&&
.DISCUSSION.../ISSUED AT 305 PM MST WED DEC 2 2009/...
SHORT TERM...TONIGHT THROUGH FRIDAY...
UPPER LOW DRIFTING INTO SERN ND CURRENTLY AND MODELS IN AGREEMENT
MOVING THIS SLOWLY SSE INTO NORTHERN IOWA BY MIDDAY THU. NW FLOW
ALOFT OVER THE CWA WILL BECOME NORTHERLY TONIGHT. ALTHOUGH THE
VORTICITY WRAPPING AROUND THE BACK OF THE UPPER LOW IS MAINLY
CHANNELED...THERE WILL BE ENOUGH MOISTURE AND DYNAMICS TO PRODUCE
SCATTERED AREAS OF LIGHT SNOW OR FLURRIES TONIGHT AND THU MORNING
ESPECIALLY EAST OF A KCPR-KLAR LINE. THESE WILL DIMINISH EITHER
THU AFTERNOON OR EVENING WITH CLOUDS DECREASING LATER THU NIGHT.
OF COURSE...COLD TEMPS ARE THE MAIN WX CONCERN AND THEY WILL BE
STAYING THAT WAY THROUGH THURSDAY NIGHT BEFORE MODERATING FRIDAY
AS A NARROW SHORTWAVE RIDGE BUILDS IN FROM THE WEST. HAVE GONE
LOWER THAN GUIDANCE AT MOST LOCATIONS TONIGHT/THU...KLAR HAS NOT
EVEN HIT 10 YET TODAY. MIN TEMPS TONIGHT WILL BE TRICKY THOUGH AS
CLOUDS SPREAD DOWN FROM THE NORTH.
LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...
MODELS SEEM TO DIFFER ON PLACEMENT OF UPPER LOW OVER THE PAC NW AT
THE END OF THE EXTENDED PERIOD AND ALSO THE PLACEMENT OF THE UPPER
TROUGH AXIS OVER THE WEST. WILL GO WITH A BLEND OF ECMWF...GFS AND
ENSEMBLE MEAN. NW FLOW WILL BE ALOFT OVER THE CWA FRIDAY NIGHT AS A
BRIEF UPPER RIDGE WEAKENS OVER THE AREA. W TO SW FLOW WILL DEVELOP
ALOFT SAT AS THE BROAD UPPER TROUGH DEEPENS OVER THE WESTERN U.S.
THE UPPER LOW WILL BE IN THE VICINITY OF ID. SKIES WILL BE PARTLY
CLOUDY OVER THE CWA FRI NIGHT AND SAT AND A COLD FRONT WILL MOVE
ACROSS THE FORECAST AREA BY SAT EVENING. THIS WILL RESULT IN VERY
COLD TEMPERATURES ONCE AGAIN ON SUN WITH A CHANCE OF LIGHT SNOW
ACROSS THE AREA. WESTERLY FLOW WILL BE ALOFT SUN AS THE UPPER
TROUGH STRETCHES WEST OF THE PAC NW COAST WITH THE AXIS ORIENTED IN
AN WEST-EAST DIRECTION. THE UPPER TROUGH AXIS WILL MOVE TOWARDS THE
AREA MON AND MON NIGHT WITH TEMPS MODERATING A BIT AHEAD THIS NEXT
IMPULSE. SNOW WILL DEVELOP ACROSS THE WY PORTION OF THE CWA BY TUES
MORNING. BRISK CONDITIONS WILL OCCUR TUESDAY AS THE UPPER TROUGH
MOVES ACROSS THE FORECAST AREA...RESULTING IN A CHANCE OF LIGHT SNOW
FOR THE CWA. FINALLY ON WED...A BIT WARMER CONDITIONS WILL OCCUR AS
W TO NW FLOW DEVELOPS ALOFT AS ANOTHER BRIEF RIDGE MOVES OVER THE
AREA AHEAD OF THE NEXT UPPER TROUGH WHICH WILL SHIFT THE UPPER FLOW
BACK TO THE SW WED NIGHT. HIGH TEMPERATURES WILL BE FROM 15 TO 20
DEGREES BELOW NORMAL THROUGH MUCH OF THE EXTENDED PERIOD...THEN 5 TO
10 DEGREES BELOW NORMAL ON WED.
&&
.AVIATION...PREVAILING CONDITIONS WILL BE VFR OVERALL TONIGHT/THU
BUT CEILINGS AND VSBYS WILL LOWER INTO MVFR CATEGORY IN SCATTERED
AREAS OF LIGHT SNOW OR FLURRIES MAINLY OVER NORTHERN AND EASTERN
PARTS OF CWA. IFR CEILINGS AND VISIBILITIES IN FOG WILL REMAIN OVER
PARTS OF THE LARAMIE VALLEY THROUGH 15Z...INCLUDING THE AIRPORT AT
KLAR. CLOUDS WILL DECREASE FROM WEST TO EAST THURSDAY NIGHT.
&&
.FIRE WEATHER...NO FIRE WEATHER CONCERNS EXPECTED THROUGH THURSDAY.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&
$$
SHORT TERM/AVIATION/FIRE WEATHER...JLH
LONG TERM...KMD
UPDATE...WEILAND
