FXUS65 KMSO 051012
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
312 AM MST SAT DEC 5 2009

...SNOW ALONG THE CONTINENTAL DIVIDE TODAY FOLLOWED BY INCREASING
NORTHEAST WINDS AND BITTERLY COLD AIR INVADING THE NORTHERN
ROCKIES TONIGHT CONTINUING INTO MIDWEEK...

.DISCUSSION...
TODAY...THE INITIAL UPPER TROUGH OF LOW PRESSURE HAS PASSED TO
THE SOUTH OF THE NORTHERN ROCKIES REGION. THE BULK OF THE
PRECIPITATION IN THE WAKE OF THIS SYSTEM IS EXPECTED TO BE
GENERALLY LIGHT...WITH SOME ACCUMULATING SNOW STILL ON TAP NEAR
THE CONTINENTAL DIVIDE...THANKS TO ADDITIONAL TOPOGRAPHIC
ENHANCEMENT. A NORTHEAST FLOW ALOFT WILL CONTINUE TO FEED COLD
CANADIAN AIR INTO WESTERN MONTANA AND NORTH-CENTRAL IDAHO
MAINTAINING BELOW NORMAL TEMPERATURES.

TONIGHT THROUGH SUNDAY NIGHT...A SECOND STRONGER SURGE OF ARCTIC 
AIR WILL PLUNGE SOUTH OUT OF CENTRAL CANADA AND BEGIN TO FLOOD
WEST OF THE CONTINENTAL DIVIDE TONIGHT. THE INTRODUCTION OF ARCTIC
AIR WILL TIGHTEN THE SURFACE PRESSURE GRADIENT...INCREASING
NORTHEAST SURFACE WINDS ACROSS MUCH OF WESTERN MONTANA. THESE
WINDS WILL HAVE A TWO-FOLD IMPACT: FIRST...WIND CHILL VALUES WILL
LOWER TO DANGEROUS LEVELS. SECONDLY...STRONG SURFACE WINDS WILL BE
BLOWING THE RECENTLY FALLEN SNOW AROUND REDUCING VISIBILITIES AND
IMPACTING AREA TRAVEL. ANY ADDITIONAL SNOWFALL TONIGHT WILL BE
CONFINED TO AN AREA RIGHT ALONG THE CONTINENTAL DIVIDE...WITH ONLY
MINOR AMOUNTS EXPECTED.

MONDAY THROUGH SATURDAY...THE MODELS CONTINUE TO INDICATED THAT
THE BROAD TROUGH WILL LINGER OVER THE REGION...MAYBE EVEN LONGER
THEN PREVIOUSLY FORECASTED. CURRENT GUIDANCE IS SHOWING THE MONDAY
AND MONDAY NIGHT SHOULD BE THE COLDEST PERIODS...BUT TUESDAY COULD
BE AS COLD AS MONDAY. FINALLY COME THE MIDDLE OF THE WEEK THE
TROUGH WILL MOVE OFF TO THE EAST LEAVING THE REGION IN
NORTHWESTERLY FLOW. THIS FLOW PATTERN WILL HELP MODERATE THE COLD
AIR MASS...BUT IT WILL BE A GRADUAL PROCESS. MONDAYS TEMPERATURES
WILL BE AROUND 30 DEGREES BELOW SEASON NORMALS...CLOSE TO RECORD
TEMPERATURES. WHILE TEMPERATURES BY SATURDAY SHOULD STILL BE
AROUND 5 TO 10 DEGREES BELOW NORMAL. THE TROUGH AND NORTHWESTERLY
FLOW WILL HAVE DIFFICULTY BRINGING ANY KIND OF MOISTURE INTO THE
NORTHERN ROCKIES. THE SHOWERS THAT DO DEVELOP WILL BE FAIRLY LIGHT
WITH LITTLE TO NO NEW SNOW ACCUMULATIONS.

&&

.AVIATION...A SYSTEM DROPPING IN FROM THE NORTH WILL CONTINUE TO
SPREAD LIGHT SNOW OVER NORTHWEST MONTANA THIS MORNING. THE SNOW
WILL SPREAD THROUGHOUT THE REMAINDER OF THE NORTHERN ROCKIES
TODAY. WIDESPREAD MVFR CEILINGS AND VISIBILITIES ARE LIKELY...WITH
LOCAL IFR POSSIBLE. BLOWING SNOW COULD FURTHER REDUCE VISIBILITIES
THIS AFTERNOON AND EVENING...ESPECIALLY TIGHT CANYONS AND PASSES
ALONG THE CONTINENTAL DIVIDE.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WIND CHILL WARNING FROM 8 PM THIS EVENING TO 11 AM MST MONDAY 
     FOR BUTTE/BLACKFOOT REGION-FLATHEAD/MISSION VALLEYS-
     POTOMAC/SEELEY LAKE REGION-WEST GLACIER REGION.

     WIND CHILL ADVISORY FROM 8 PM THIS EVENING TO 11 AM MST MONDAY 
     FOR BITTERROOT/SAPPHIRE MOUNTAINS-KOOTENAI/CABINET REGION-
     LOWER CLARK FORK REGION-MISSOULA/BITTERROOT VALLEYS.

     WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR 
     POTOMAC/SEELEY LAKE REGION-WEST GLACIER REGION.

ID...NONE.
&&

$$

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