FXUS65 KMSO 061035
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
335 AM MST SUN DEC 6 2009

...ARCTIC AIR...STRONG WINDS...AND DANGEROUS WIND CHILLS EXPECTED
TO BEGIN TONIGHT AND CONTINUE THROUGH MONDAY...

.DISCUSSION...
TODAY THROUGH MONDAY NIGHT...A BROAD TROUGH OF LOW PRESSURE WILL
EXTEND FROM SOUTH-CENTRAL CANADA THROUGH THE NORTHERN ROCKIES INTO
THE PACIFIC NORTHWEST THROUGH THE PERIOD. VERY COLD AIR WILL BE
MOVING INTO WESTERN MONTANA TODAY AS THE NEXT SURGE OF ARCTIC AIR
FLOODS INTO WEST OF THE CONTINENTAL DIVIDE. LIGHT SNOWFALL WILL BE
TAPERING OFF DURING THE DAY TODAY WITH LITTLE IN THE WAY OF
ADDITIONAL ACCUMULATION EXPECTED. THE BIGGEST IMPACT STILL TO BE
DEALT WITH WILL BE STRONG NORTHEAST WINDS AND DANGEROUS WIND
CHILL VALUES. SURFACE WINDS WILL BE DECREASING ACROSS THE REGION
LATER MONDAY AND MONDAY NIGHT AS THE SURFACE PRESSURE GRADIENT
RELAXES AND WINDS ALOFT DIMINISH. HOWEVER...VERY COLD AIR WILL
REMAIN FIXED OVER THE REGION. EARLY TUESDAY MORNING...DECREASED
WINDS AND PARTIAL CLEARING COULD SET UP CONDITIONS FAVORABLE FOR
THE COLDEST TEMPERATURES THUS FAR THIS FALL.

TUESDAY THROUGH SUNDAY...THE MODELS ARE CONSISTENT WITH
NORTHWESTERLY FLOW PERSISTING OVER THE NORTHERN ROCKIES THROUGH
THE MIDDLE OF THE WEEK. THIS FLOW PATTERN WILL CAUSE A VERY
GRADUAL WARMING TREND. TEMPERATURES FOR TUESDAY SHOULD STILL BE
AROUND 25 DEGREES BELOW SEASON NORMALS WHILE BY FRIDAY
TEMPERATURES ARE EXPECTED TO BE AROUND 5 DEGREES BELOW NORMAL. THE
LATEST RUN OF THE MODELS ARE INDICATING THAT THE FLOW PATTERN WILL
BECOME SPLIT OVER THE WESTERN UNITED STATES WITH DISTURBANCES
BEING NORTH AND SOUTH OF THE NORTHERN ROCKIES. THE TEMPERATURES
FOR THE WEEKEND COULD POTENTIAL BE NEAR TO ABOVE SEASON
NORMALS...BUT DUE TO RECENT SHOWING OF THIS SOLUTION HAVE DECIDED
TO TREND TEMPERATURES.

&&

.AVIATION...AN UNSTABLE COLD TROUGH WILL CONTINUE TO SETTLE OVER
THE NORTHERN ROCKIES TODAY. THE BIGGEST IMPACT OF THE TROUGH WILL
BE THE COLD AIR FILTERING INTO THE VALLEYS OF WESTERN MONTANA.
MOST VALLEY LOCATIONS WILL SEE GUSTY EASTERLY WINDS TODAY...WITH
THE STRONGEST GUSTS EXPECTED THIS AFTERNOON. THIS TROUGH WILL
KEEP CEILINGS RELATIVELY LOW CAUSING MOUNTAINS AND PASSES TO BE
OBSCURED. ALSO THE INSTABILITY WILL KEEP A FEW LINGER SNOW SHOWERS
AROUND.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WIND CHILL WARNING UNTIL 11 AM MST MONDAY FOR BUTTE/BLACKFOOT 
     REGION-FLATHEAD/MISSION VALLEYS-POTOMAC/SEELEY LAKE REGION-
     WEST GLACIER REGION.

     WIND CHILL ADVISORY UNTIL 11 AM MST MONDAY FOR 
     BITTERROOT/SAPPHIRE MOUNTAINS-KOOTENAI/CABINET REGION-LOWER 
     CLARK FORK REGION-MISSOULA/BITTERROOT VALLEYS.

     WINTER WEATHER ADVISORY UNTIL 10 AM MST THIS MORNING FOR 
     FLATHEAD/MISSION VALLEYS.

ID...WIND CHILL ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR WESTERN 
     LEMHI COUNTY.

     WIND CHILL ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR EASTERN 
     LEMHI COUNTY.

&&

$$

SHORT TERM...MSJ
LONG TERM....SMITH
AVIATION...SMITH