FXUS65 KCYS 290357
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
857 PM MST SAT NOV 28 2009

.UPDATE...BASED ON TRENDS AND LATEST RUNS OF THE NAM...HAVE MADE
SOME MODIFICATIONS TO TEMPERATURES...DEWPOINTS...WINDS...CLOUD
COVER...SNOW SHOWER COVERAGE FOR THE REST OF THE NIGHT. ALSO ADDED
MENTION OF AREAS OF FOG IN LOCATIONS WHERE THE TEMPERATURE AND
DEWPOINT SPREADS ARE NARROWING WITH DECREASING CLOUD COVER AND
WHERE NAM BOUNDARY LAYER PROGS SUGGEST MOST LIKELY FOG FORMATION.
RUBIN

&&

.AVIATION...VFR THE REST OF THE NIGHT...EXCEPT FOR SCATTERED AREAS
OF MVFR AND IFR IN SNOW SHOWERS AND FOG WEST OF A CASPER TO 
CHEYENNE LINE.  RUBIN

&&

.PREV DISCUSSION... /ISSUED 1226 PM MST SAT NOV 28 2009/ 

SHORT TERM...TONIGHT THROUGH MONDAY...

18Z SURFACE ANALYSIS HAS 2MB HEIGHT RISES IN THE CWA ASSOCIATED
WITH ANOTHER SURGE OF COLD AIR. THIS IS CAUSING SOME GUSTY WINDS
ESPECIALLY FROM CHEYENNE EAST TO SIDNEY BUT NO SNOW HAS BEEN
REPORTED YET AND RADAR NOT SHOWING ANY RETURNS. WATER VAPOR
SHOWING THE SPINNING LOW OVER SOUTHERN CALIFORNIA AND A TROUGH
FROM NE MONTANA INTO SOUTHEAST IDAHO IN THE SPLIT FLOW.

MODELS INDICATE THIS UPPER TROUGH SHOULD MOVE ACROSS THE CWA
DURING THE EVENING HOURS WITH PRECIPITATION PRETTY MUCH CONFINED
TO THE HIGHER ELEVATIONS AND SHOULD BE DONE BY 06Z TONIGHT. IN
ADDITION GUIDANCE INDICATES THAT THE WINDS SHOULD BEGIN TO DIE
DOWN AFTER SUNSET THIS EVENING.

AFTER TROUGH PASSES THIS EVENING LEADING EDGE OF UPPER RIDGE WILL
GIVE THE CWA NORTHWEST FLOW THROUGH THE END OF THE FORECAST PERIOD
WITH LITTLE IF ANY SENSIBLE WEATHER.

TEMPERATURES WILL BE COLD AGAIN ON SUNDAY WITH A SLIGHT WARMING
TREND ON MONDAY WITH SOME AREAS EAST OF INTERSTATE 25 MAKING IT
BACK INTO THE 50S.

LONG TERM...MONDAY NIGHT THROUGH FRIDAY NIGHT...RIDGING WILL BE 
OVERHEAD MONDAY NIGHT AND WILL PUSH OFF TO THE EAST BY TUESDAY 
MORNING. AN UPPER TROUGH WILL DIG ACROSS SOUTHERN CANADA AND INTO 
THE NORTHERN PLAINS BY TUESDAY MORNING. A COLD FRONT ASSOCIATED WITH 
THE SYSTEM WILL DROP SOUTH ACROSS THE CWA IN THE AFTERNOON ON 
TUESDAY BUT MODELS DO NOT SHOW MUCH MOISTURE ASSOCIATED WITH IT. SO 
KEPT CHANCE POPS IN THE MOUNTAINS TO ACCOUNT FOR OROGRAPHIC DYNAMICS 
WITH LOW POPS ELSEWHERE. NORTH WINDS WILL BE GUSTY BEHIND THE FRONT 
AND WILL EASE OVERNIGHT AS SFC HIGH PRESSURE SLIDES ACROSS THE AREA. 
TEMPS WILL BE COOLER FOR WEDNESDAY AND THURSDAY AS HIGH PRESSURE 
REMAINS AT THE SFC UNDER NNW FLOW ALOFT. WINDS AT THE SFC WILL BE 
TYPICAL BREEZY ON THURSDAY AND FRIDAY AS SFC HIGH PRESSURE SLIDES
TO THE EAST AND LEE TROUGH RETURNS TO THE PLAINS. MODELS HINT AT
ANOTHER WAVE DIGGING INTO THE PACIFIC NW FRI BUT DIFFER
SIGNIFICANTLY WITH TIMING OF THE SYSTEM. 12Z GFS AND CANADIAN BOTH
HAVE THE TROUGH MOVING OVER IDAHO AND MONTANA BY 12Z FRIDAY WHERE
THE ECMWF AND GFS ENSEMBLE MEAN KEEP IT OFFSHORE WITH RIDGE OVER
THE NORTHERN ROCKIES...WHICH IS CONSISTENT WITH THE PREVIOUS MODEL
RUN. SO WENT WITH A DRIER AND WINDIER FORECAST BASED ON THE MORE
CONSISTENT MODEL RUNS. TEMPS WILL STILL BE ON THE COOL SIDE FRIDAY
AND FRIDAY NIGHT.

AVIATION...MAIN AVIATION CONCERN THIS AFTERNOON WILL BE THE GUSTY
NORTHERLY WINDS BUT SHOULD DIE DOWN AFTER SUNSET. SOME ISOLATED
SNOW SHOWERS WILL BE LOCATED MAINLY OVER THE HIGHER ELEVATIONS
OF SOUTHEAST WYOMING THROUGH THIS EVENING BUT NOT HAVE ANY
SIGNIFICANT IMPACTS ON ANY AERODROMES.

FIRE WEATHER...NO FIRE WEATHER CONCERNS AT THIS TIME.

&&

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

&&

$$

SHORT TERM/AVIATION...GRIFFITH
LONG TERM...RJM