FXUS65 KMSO 010457
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
957 PM MST MON NOV 30 2009

.UPDATE...INCREASED CHANCES FOR PRECIPITATION IN THE GRANGEVILLE/
CAMAS PRAIRIE REGION FOR TUESDAY MORNING.

&&

.DISCUSSION...MODEL CROSS SECTIONS AND SOUNDINGS OVER GRANGEVILLE
SHOW SUFFICIENT LOW LEVEL MOISTURE AND OROGRAPHIC LIFT FOR LIGHT
SNOW ACCUMULATIONS TUESDAY MORNING. THE BEST CHANCES FOR SNOW LOOK
TO BE CENTERED AROUND 15Z/700AM PST. LIGHT ACCUMULATIONS OF AROUND
1 INCH NEAR GRANGEVILLE AND SLIGHTLY HIGHER AMOUNTS OVER THE
WHITEBIRD GRADE ARE POSSIBLE BY MID-MORNING TUESDAY.

&&

.AVIATION...A SURFACE COLD FRONT WILL SWEEP THROUGH THE NORTHERN
ROCKIES BRINGING SNOW CHANCES AND INCREASE SURFACE WINDS TO THE
TERMINALS. NORTHERN AIRFIELDS...INCLUDING KGPI AND KMSO...WILL SEE
FRONTAL PASSAGE AND THE BEST CHANCE FOR SNOW ACTIVITY AROUND AND
AFTER THE 01/0600Z TIMEFRAME THROUGH EARLY TUESDAY MORNING. BY
01/1200Z FRONTAL PASSAGE WILL REACH KBTM AND KSMN...TURNING WINDS
NORTHERLY...INCREASING CLOUDS AND CHANCES FOR SHOWER ACTIVITY.
VISIBILITIES AND CEILINGS HAVE THE POTENTIAL TO BE LOWERED
SIGNIFICANTLY UNDER THE HEAVIEST SHOWERS. EXPECT MOUNTAINS AND
PASSES TO BE OBSCURED BY SHOWER ACTIVITY AND CLOUDS. BEHIND THE
INITIAL PRECIPITATION BURST BY THE FRONT...MOSTLY BROKEN TO
OVERCAST SKIES AND MAINLY TERRAIN LOCKED SHOWERS WILL REMAIN WITH
MOSTLY NORTHERLY WINDS THROUGH TUESDAY.

&&

.PREV DISCUSSION... /ISSUED 245 PM MST MON NOV 30 2009/ 

..TEMPERATURES TURNING COLDER...

DISCUSSION...TONIGHT THROUGH THURSDAY...A WEAKENING COLD FRONT
WILL DRIFT SOUTHWARD ACROSS NORTH CENTRAL IDAHO AND WESTERN
MONTANA TONIGHT. THIS WILL BE FOLLOWING BY A FAST MOVING AND MORE
ORGANIZED WEATHER DISTURBANCE THAT WILL SWEEP SOUTHEASTWARD ACROSS
MAINLY WESTERN MONTANA LATE TONIGHT AND TUESDAY MORNING.
PRECIPITATION WILL BE ON THE LIGHT SIDE AND MAINLY CONFINED TO THE
HIGHER TERRAIN OF NORTHWEST MONTANA WITH THE INITIAL WEAKENING
COLD FRONT. HOWEVER...A FAIRLY MOIST AND UNSTABLE LOWER ATMOSPHERE
WILL COMBINE WITH THE ENERGY FROM THE SECOND WEATHER DISTURBANCE
TO PRODUCE A BETTER THREAT OF PRECIPITATION LATE TONIGHT INTO
TUESDAY MORNING. WE HAVE ISSUED A WINTER WEATHER ADVISORY FOR
GLACIER PARK WHERE OROGRAPHIC FORCING SHOULD COMBINE WITH THE
WEATHER FEATURES ABOVE. SIGNIFICANTLY COLDER AIR WILL SHIFT
SOUTHWARD OVER THE REGION TUESDAY AND WEDNESDAY. THIS COLDER
AIR...COMBINED WITH GENERALLY CLEAR SKIES AND LONG NIGHTS SHOULD
SUPPORT A PERIOD OF MUCH COOLER CONDITIONS INTO AT LEAST THURSDAY.

THURSDAY NIGHT INTO FRIDAY...THE MODELS CONTINUE TO STRUGGLE ON
HOW A WEATHER DISTURBANCE WILL BE MOVING INTO THE WESTERN UNITED
STATES FOR THE END OF THE WEEK. THE GFS CONTINUES TO SHOW A
SIGNIFICANT SYSTEM DROPPING OUT OF BRITISH COLUMBIA CAUSING WIDESPREAD
PRECIPITATION ON FRIDAY FOR THE NORTHERN ROCKIES. MEANWHILE...THE ECMWF
CONSISTENTLY SHOWS A CUTOFF LOW PRESSURE SYSTEM DEVELOPING JUST
OFF THE COAST WHICH LEAVES THE NORTHERN ROCKIES UNDER A SHORTWAVE
RIDGE. SO AT THIS TIME HAVE LITTLE CONFIDENCE IN THE MODEL
SOLUTIONS...SO WENT WITH CLIMATOLOGY POPS AND TEMPERATURES.

SATURDAY THROUGH SUNDAY...EVEN THOUGH THE MODELS DISAGREE ON
FEATURES FOR THE END OF THE WEEK...THEY COME IN FAIRLY GOOD
AGREEMENT FOR THE WEEKEND. BOTH THE ECMWF AND GFS SHOW A BROAD
TROUGH DEVELOPING OVER THE REGION. A FAIRLY STRONG SURFACE HIGH WILL
DROP PRACTICALLY DUE SOUTH OUT OF ALBERTA. THIS HIGH PRESSURE
WILL BE ACCOMPANIED BY A DEEP ARCTIC AIR MASS PUSHING INTO THE
AREA. TEMPERATURES FOR THE WEEKEND ARE CURRENTLY FORECAST TO BE
AROUND 10 DEGREES BELOW SEASONAL NORMALS...BUT HAVE THE POTENTIAL
TO BE EVEN COOLER AROUND 20 DEGREES BELOW NORMAL. ALSO THIS BROAD
TROUGH WILL BE FAIRLY UNSTABLE WITH PRIMARILY OROGRAPHIC
SHOWERS...ESPECIALLY ALONG THE CONTINENTAL DIVIDE.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WEST GLACIER 
     REGION.

ID...NONE.
&&

$$

SHORT TERM...KITSMILLER
LONG TERM....BAUCK
AVIATION...KITSMILLER