FXUS65 KMSO 261055
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
355 AM MST THU NOV 26 2009

.DISCUSSION...THE UPPER LEVEL RIDGE OF HIGH PRESSURE HAS BEGUN TO
FLATTEN AND SLOWLY WEAKEN THIS MORNING...ALLOWING HIGHER LEVEL
CLOUD COVER TO MOVE OVER CENTRAL IDAHO AND WESTERN MONTANA. THIS HAS
SERVED TO KEEP TEMPERATURES IN SOME LOCATIONS FROM DROPPING TOO
FAR BUT WITH THOSE WHO SAW BREAKS IN THE CLOUDS DROPPING ABOUT
TEN DEGREES COOLER THAN YESTERDAY. AS SUCH ANTICIPATE HIGH
TEMPERATURES TO BE VERY TRICKY FOR THIS AFTERNOON SINCE THOSE
COOLER VALLEY LOCATIONS WILL REMAIN UNDER THE INFLUENCE OF STRONG
TEMPERATURE INVERSIONS AND LIKELY NOT WARM AS MUCH AS THEY DID
YESTERDAY. WHILE OTHERS...WHO HAVE REMAINED WARMER OVERNIGHT...
COULD POTENTIALLY REACH HIGH TEMPERATURES SIMILAR TO YESTERDAYS
VALUES DESPITE STRONG INVERSIONS AT THE SURFACE. THE OTHER IMPACT
FOR TODAY WILL BE THE LONGEVITY OF LOCALLY DENSE FOG...WHICH HAS
PLAGUED THE AIRPORT IN KALISPELL OVERNIGHT AND RECENTLY DEVELOPED
IN MISSOULA. BELIEVE FOG WILL LIKELY PERSIST THROUGH AT LEAST THE
LATE MORNING BEFORE THE ATMOSPHERE SLOWLY BEGINS TO MODERATE DUE
TO AFTERNOON HEATING AND LIFT THE FOG. BUT HAZY CONDITIONS WILL
LIKELY CONTINUE THROUGH MUCH OF THE AFTERNOON SINCE SURFACE WIND
SPEEDS IN MOST LOCATIONS ARE EXPECTED TO REMAIN LIGHT.

TONIGHT THINGS BEGIN TO CHANGE AS AN APPROACHING PACIFIC WEATHER
SYSTEM MOVES INLAND AND IMPACTS THE NORTHERN ROCKIES WITH COLDER
TEMPERATURES AND SNOW. FORECAST MODELS HAVE TRENDED DRAMATICALLY
TOWARDS A SPLITTING SYSTEM WITH THE MOST ENERGETIC PORTIONS OF THE
TROUGH DIGGING QUICKLY INTO CALIFORNIA. THERE IS...HOWEVER...A
FAIRLY ENERGETIC UPPER AND MID LEVEL TROUGH WHICH WILL MOVE
THROUGH THE NORTHERN ROCKIES TONIGHT THROUGH LATE FRIDAY. AS THE
SURFACE LOW AND ASSOCIATED COLD FRONT PASS ALONG THE CANADIAN
BORDER...JET ENERGY APPEARS TO HELP ENHANCE DYNAMIC LIFT WITH
THIS SYSTEM RESULTING BETTER CHANCES FOR SNOWFALL. GIVEN THE
TRAJECTORY OF THIS SYSTEM...BELIEVE NORTHWEST MONTANA...THE
CLEARWATER MOUNTAINS AND CONTINENTAL DIVIDE MOUNTAINS NORTH OF
HIGHWAY 200 STAND IN AN AREA FAVORED FOR HEAVIER SNOWFALL AMOUNTS.
AT THIS TIME ADVISORY AMOUNTS OF SNOWFALL (4-8 INCHES) APPEAR
POSSIBLE...ESPECIALLY IN THE MOUNTAINS AND OVER PASSES IN THESE
FAVORED LOCATIONS. THE BIGGEST QUESTION WITH THIS SYSTEM REMAINS
TO BE SNOW LEVELS AND HOW QUICKLY THEY FALL PROCEEDING THE FRONT.
IN ADDITION...THE POTENTIAL FOR GUSTY WINDS OVER THE CAMAS PRAIRIE
AND GRANGEVILLE ARE POSSIBLE JUST BEFORE AND ALONG THE COLD FRONT.

SUNDAY... THE NORTHERN ROCKIES WILL REMAIN UNDER THE INFLUENCE OF AN 
EXITING WEATHER SYSTEM WITH A CHANCE OF SNOW.

MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT WITH THE NEXT WEATHER 
PRODUCER PROJECTED TO ARRIVE IN THE PACIFIC NORTHWEST ON MONDAY AND 
THROUGH THE NORTHERN ROCKIES ON TUESDAY. THIS WEATHER SYSTEM LOOKS 
TO BE IN THE FORM OF A COLD LOW PRESSURE TROUGH WITH THE POTENTIAL 
FOR SNOW DOWN TO MOST VALLEY FLOORS. BY THURSDAY A RIDGE OF HIGH 
PRESSURE WILL BE BUILDING INTO THE REGION. 

&&

.AVIATION...DRAMATICALLY REDUCED VISIBILITY AND EXTREMELY LOW
CEILING HEIGHTS CAN BE EXPECTED AT KMSO AND KGPI THIS MORNING
SINCE FREEZING FOG HAS DEVELOPED OVERNIGHT. EXPECT VERY STABLE
CONDITIONS AT THE SURFACE TO KEEP FOG IN THE FORECAST THROUGH AT
LEAST 18Z BEFORE WARMING TEMPERATURES HELP TO MODERATE THE
ATMOSPHERE SOME AND LIFT THE FOG. TERRAIN OBSCURATION CAN ALSO BE
EXPECTED DUE TO LOW STRATUS HUGGING AGAINST THE MOUNTAINS.

&&

.AIR STAGNATION...ALTHOUGH THE RIDGE OF HIGH PRESSURE HAS BEGUN TO
SLOWLY WEAKEN...VERY STABLE CONDITIONS AT THE SURFACE WILL PREVENT
WIND FROM DEVELOPING AND KEEP THE ATMOSPHERE STAGNANT THROUGH THIS
AFTERNOON. AN APPROACHING PACIFIC WEATHER SYSTEM IS STILL EXPECTED
TO MOVE INTO THE REGION TONIGHT WITH A COLD FRONT PASSAGE ANTICIPATED
FRIDAY AFTERNOON. THIS WILL HELP TO MIX THE LOWER ATMOSPHERE AND
REDUCE THE AMOUNT OF ACCUMULATED POLLUTANTS.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
ID...NONE.
&&

$$

SHORT TERM...DICKERSON
LONG TERM....KOLATA
AVIATION...DICKERSON