FXUS65 KMSO 221214 AAA
AFDMSO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MISSOULA MT
514 AM MST TUE DEC 22 2009

.UPDATE...ISSUED A WINTER WEATHER ADVISORY FOR THE GLACIER PARK
AREA FOR TONIGHT AND WEDNESDAY.

&&

.DISCUSSION...SNOWFALL ACCUMULATIONS TONIGHT THROUGH WEDNESDAY
MORNING WILL BE ENOUGH TO WARRANT A WINTER WEATHER ADVISORY OVER
THE GLACIER PARK AREA. HIGHWAY 2 BETWEEN WEST GLACIER AND MARIAS
PASS WILL BE IMPACTED BY THIS SNOWFALL. PLEASE SEE
WWW.WEATHER.GOV FOR FURTHER DETAILS.

&&

.AVIATION...A SLOW MOVING COLD FRONT...CURRENTLY LOCATED ALONG A
LINE FROM KGPI TO KMYL...WILL CREATE SEVERAL AVIATION CONCERNS
TODAY. AHEAD OF THE COLD FRONT...VALLEY FOG CONTINUES TO PLAGUE
WEST CENTRAL AND SOUTHWEST MONTANA INCLUDING AIRFIELD KMSO WITH
LOW VISIBILITY. EXPECT THE FOG TO LIFT WITH THE APPROACH OF THE
COLD FRONT...AROUND 22/12Z FOR KMSO. BEHIND THE FRONT...WIDESPREAD
PRECIPITATION WILL CAUSE LOWERED CEILINGS AND VISIBILITY WHICH
WILL OBSCURE THE HIGHER TERRAIN. PRECIPITATION BEHIND THE FRONT IS
EXPECTED TO FALL AS SNOW DOWN TO AROUND 2500 FEET.

&&

.PREV DISCUSSION... /ISSUED 401 AM MST TUE DEC 22 2009/ 

DISCUSSION...MOISTURE IS SPREADING INTO THE NORTHERN ROCKIES
AHEAD OF A PACIFIC LOW PRESSURE SYSTEM THAT IS CURRENTLY MOVING
INTO WASHINGTON AND OREGON. A MIXTURE OF RAIN AND SNOW IS
CURRENTLY FALLING OVER MUCH OF IDAHO AND IS NOW MOVING INTO
WESTERN MONTANA. AN ASSOCIATED COLD FRONT IS MOVING THROUGH THE
REGION AS WELL WHICH WILL CONTINUE TO CAUSE SNOW LEVELS TO DROP
THROUGH THE DAY. WEST-CENTRAL IDAHO HAS SEEN SNOW ACCUMULATIONS
DOWN TO 3500 FEET. BECAUSE OF THE SNOW ACCUMULATION BEING
OBSERVED ON THE GREER AND WHITEBIRD GRADES IN IDAHO DECIDED TO
ISSUE A WINTER WEATHER ADVISORY FOR THIS MORNING. AND SNOW LEVELS
SHOULD CONTINUE TO DROP THIS MORNING BRINGING ACCUMULATIONS TO
LOWER ELEVATIONS. AS THE LOW DIGS INTO THE GREAT BASIN THIS
AFTERNOON AN AREA OF ENHANCED FORCING WILL SET UP OVER THE
IDAHO/MONTANA BORDER WHICH COULD POTENTIALLY BRING LIGHT TO
MODERATE SNOWFALL TO MISSOULA. BECAUSE OF THE UNCERTAINTY OF THE
LOCATION OF THE HEAVIEST SNOWFALL WENT ON THE LIGHTER SIDE. 

A SECONDARY TROUGH OF LOW PRESSURE WILL MOVE OUT OF WESTERN CANADA
AND INTO IDAHO AND MONTANA ON WEDNESDAY. THIS WILL BRING ANOTHER
SHOT OF MOISTURE AND COLDER AIR. MANY LOCATIONS WILL SEE AT LEAST
SOME LIGHT SNOWFALL...BUT THE MOST LIKELY LOCATIONS FOR HEAVIER
SNOWFALL WILL BE ALONG THE DIVIDE IN THE WEST GLACIER/BOB MARSHALL
/SEELEY-SWAN REGIONS.

A COOL AND DRY NORTHERLY FLOW WILL SET UP OVER THE NORTHERN
ROCKIES THURSDAY AND FRIDAY AS A RIDGE OF HIGH PRESSURE BUILDS
ALONG THE WEST COAST. THIS WILL ALLOW FOR MUCH COLDER TEMPERATURES
OVER THE NORTHERN ROCKIES COMPARED TO EARLIER IN THE WEEK.

THE RIDGE OF HIGH PRESSURE IS EXPECTED TO SHIFT SLOWLY EASTWARD
FRIDAY NIGHT AND REMAIN ANCHORED OVER THE AREA THROUGH THE
WEEKEND. WITH STRENGTHENING INVERSIONS...PERSISTENT VALLEY FOG IS
EXPECTED TO FORM.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 11 AM MST 
     WEDNESDAY FOR WEST GLACIER REGION.

ID...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR LOWER 
     HELLS CANYON/SALMON RIVER REGION.

     WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR 
     OROFINO/GRANGEVILLE REGION.

&&

$$

SHORT TERM...LOEFFELBEIN
LONG TERM....PALLISTER
AVIATION...PALLISTER