FXUS65 KCYS 300353
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
853 PM MST SUN NOV 29 2009
.UPDATE...BASED ON TRENDS AND EVENING NAM MODEL...HAVE MADE MINOR
ADJUSTMENTS TO TEMPERATURES...DEWPOINTS AND WINDS FOR THE REST OF
TONIGHT. RUBIN
&&
.PREV DISCUSSION... /ISSUED 1205 PM MST SUN NOV 29 2009/
SHORT TERM...TONIGHT THROUGH TUESDAY...
SURFACE HIGH PRESSURE AND AN UPPER LEVEL RIDGE ARE BUILDING OVER
THE PACIFIC NORTHWEST WHILE A PERSIST UPPER LOW CONTINUES TO SPIN
OVER THE EXTREME SOUTHWESTERN U.S. AND OLD MEXICO.
THE UPPER RIDGE IS GIVING AND IS FORECAST TO CONTINUE TO BRING A
COLD NORTH NORTHWESTERLY FLOW TO THE CWA THROUGH MONDAY. MONDAY
NIGHT INTO TUESDAY AN UPPER SYSTEM WILL MOVE QUICKLY EAST ALONG
THE U.S. AND CANADIAN BORDER AND WILL DRIVE A SURFACE COLD FRONT
INTO THE AREA BY THE END OF THE FORECAST PERIOD. AT THIS TIME THE
SHORT TERM APPEARS AS THOUGH IT WILL REMAIN DRY.
TEMPERATURES WILL BE THE FORECAST PROBLEM IN THE SHORT TERM
ESPECIALLY IN THE WESTERN PORTIONS OF THE CWA WHERE THERE ARE SOME
DIFFERENCES IN THE GUIDANCE WITH THE MET DATA KEEPING HIGHS SOME 5
DEGREES OR MORE COOLER THAN THE MAV. HAVE DECIDED TO KEEP COOLER
HIGHS IN THOSE AREAS.
SOME DENSE FOG DEVELOPED THIS MORNING IN THIS COLD AIR AND WILL GO
WITH PERSISTENCE AND HAVE FOG IN TOMORROW MORNINGS FORECAST AGAIN.
LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...
MUCH COOLER CONDITIONS WILL BE PRESENT TO START THE LONG TERM
FORECAST PERIOD FOLLOWING TUESDAYS COLD FRONTAL PASSAGE. WILL
CONTINUE THE INHERITED PRECIPITATION CHANCES WITH THE BAROCLINIC
ZONE OVERHEAD WITH NEARLY NORTH FLOW ALOFT. DYNAMICS WILL BE WEAK
AS THE JET STREAK IS EXPECTED TO BE MAINLY EAST OF THE FORECAST
AREA...BUT OROGRAPHICS COMBINED WITH WEAK MOISTURE SIGNAL SHOULD
BE ENOUGH TO PRODUCE AT LEAST A FEW SHOWERS ESPECIALLY OVER THE
HIGHER TERRAIN.
NEXT UPPER WAVE WILL BE SLIGHTLY FURTHER WEST IN THE NORTH FLOW
ALOFT AND WILL INCREASE PRECIPITATION CHANCES TO MENTIONABLE ON
WEDNESDAY NIGHT IN THE MOUNTAIN AREAS. MID LEVEL MOISTURE WILL BE
SLIGHTLY IMPROVED WITH THIS DISTURBANCE...AND OROGRAPHIC SUPPORT IN
THE MID AND UPPER NORTH-NORTHWEST FLOW SHOULD AGAIN BE ENOUGH TO
PRODUCE AT LEAST MOUNTAIN SHOWERS. WEAK WARM AIR ADVECTION AHEAD OF
A WEAK SHORTWAVE ALOFT MAY ALLOW FOR CONTINUED MOUNTAIN SHOWERS AND
A WEAK WARMUP TO NEAR NORMAL TEMPERATURES ON THURSDAY.
A SURFACE TROUGH THEN IS EXPECTED TO DEVELOP IN THE LEE OF THE
NORTHERN ROCKIES THURSDAY NIGHT AND INTO FRIDAY...WITH TEMPERATURES
AGAIN EXPECTED TO WARM TO ABOVE NORMAL VALUES FOR FRIDAY.
THE LAST SEVERAL RUNS OF THE GFS MODEL HAVE SHOWN A WIDE VARIETY OF
SOLUTIONS FOR FRIDAY AND BEYOND...BUT THE PAST FEW RUNS HAVE BEEN
TRENDING TOWARD A STRONG COLD FRONT DROPPING SOUTH INTO THE WESTERN
UNITED STATES. THE CANADIAN MODEL IS ALSO HINTING AT THIS SOLUTION.
THE EUROPEAN MODEL HAS BEEN TRENDING THE OPPOSITE DIRECTION...
STARTING WITH A DEEP COLD TROUGH ACROSS THE AREA IN PREVIOUS RUNS
FOR SATURDAY AND NOW KEEPING AN UPPER LEVEL RIDGE OVERHEAD UNTIL A
STRONG TROUGH APPROACHES EARLY NEXT WEEK.
AT THIS TIME WILL AT LEAST TREND SATURDAY THROUGH SUNDAY
PRECIPITATION CHANCES TOWARD CLIMATOLOGICAL VALUES WITH THE
POSSIBILITY OF THE GFS AND CANADIAN SOLUTIONS BRINGING A WESTERN
UNITED STATES TROUGH ACROSS THE AREA.
AVIATION...VFR CONDITIONS EXPECTED AT ALL LOCATIONS FOR THE
REMANDED OF TODAY. KRWL AND KLAR MAY SEE SOME IFR CONDITIONS WITH
FOG AND LOW CEILINGS ON MONDAY MORNING BETWEEN 11Z AND 16Z.
FIRE WEATHER...NO FIRE WEATHER CONCERNS AT THIS TIME.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&
$$
SHORT TERM/AVIATION...GRIFFITH
LONG TERM...CARPENTER
