FXUS65 KMSO 232132
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
232 PM MST WED DEC 23 2009

.DISCUSSION...TONIGHT THROUGH FRIDAY...CLOUDS AND SHOWERS WILL BE
DISSIPATING THIS EVENING AS DRIER..COLDER CANADIAN AIR MOVES INTO
THE NORTHERN ROCKIES. CLEARING SKIES AND CALM WINDS AT THE SURFACE
WILL PROMOTE STRONG RADIATIONAL COOLING TONIGHT AND AGAIN THURSDAY
NIGHT. A RIDGE OF HIGH PRESSURE WILL BE APPROACHING THE INTER-
MOUNTAIN REGION FROM THE WEST FURTHER STABILIZING THE LOWER
ATMOSPHERE THROUGH FRIDAY. AS THE AIR MASS MOISTENS BENEATH A
STRENGTHENING SURFACE-BASED INVERSION... FOG/STRATUS CAN START
DEVELOPING IN THE VALLEY AND LOWLANDS. TEMPERATURES WILL BECOME
CONSIDERABLY COLDER FOR THE NEXT FEW DAYS WITH DAYTIME HIGHS IN
THE TEENS AND LOWER 20S...AND MORNING LOWS IN THE SINGLE DIGITS.
COLDEST TEMPERATURES ARE EXPECTED ALONG THE CONTINENTAL DIVIDE
WITH NIGHT/MORNING TEMPERATURES WILL BE WELL BELOW ZERO.

THE VERY STRONG AND HIGHLY AMPLIFIED RIDGE OF HIGH PRESSURE WILL
MOVE OVER THE NORTHERN ROCKIES REGION THIS WEEKEND. LATE SATURDAY
FORECAST MODELS CONTINUE TO SHOW A PIECE OF ENERGY ROTATING SOUTH 
FROM CANADA INTO EASTERN MONTANA...DRAWN DOWN BY A VERY IMPRESSIVE
WINTER STORM OVER THE UPPER MISSISSIPPI RIVER VALLEY. THIS PIECE
OF ENERGY BECOMES ELONGATED AND BEGINS TO DRIFT WEST AS THE
MASSIVE LOW MOVES EAST INTO THE GREAT LAKES REGION. THE WEAK PIECE
OF ENERGY WILL GRADUALLY MEANDER ITS WAY WEST...THROUGH THE RIDGE
TOWARDS IDAHO BY SUNDAY. THIS FEATURE WILL DO LITTLE TO INFLUENCE
THE STRONG VALLEY INVERSIONS...COLD TEMPERATURES AND FREEZING FOG
WHICH IS EXPECTED TO DEVELOP ACROSS MUCH OF WESTERN MONTANA BY
WEEKS END. HOWEVER...IT COULD PROVIDE SOME HIGHER CLOUD COVER
ACROSS SOUTHWEST MONTANA (BUTTE) AND CENTRAL IDAHO 
(GRANGEVILLE/SALMON) POSSIBLY HINDERING THE DEVELOPMENT OF 
INVERSIONS...KEEPING TEMPERATURES SLIGHTLY WARMER AND REDUCE THE
POTENTIAL FOR WIDESPREAD FREEZING FOG. BUT OVERALL DO ANTICIPATE
TEMPERATURES WELL BELOW NORMAL...BELOW ZERO IN SOME 
LOCATIONS...THROUGH THE WEEKEND WITH AREAS OF FREEZING FOG LIKELY.

WEAK FLOW ALOFT WILL PREVAIL THROUGH THE BEGINNING OF NEXT WEEK
WITH FORECAST MODELS HINTING AT A RETURN MORE ACTIVE WEATHER
(MOUNTAIN SNOW) BY 2010. TEMPERATURES WILL SLOWLY MODERATE WITH
PRECIPITATION CHANCES INCREASING BY THE NEW YEAR.

&&

.AVIATION...CLOUDS AND SHOWERS WILL BE DISSIPATING THIS EVENING AS
DRIER..COLDER CANADIAN AIR MOVES INTO THE NORTHERN ROCKIES.
CLEARING SKIES AND CALM WINDS AT THE SURFACE WILL PROMOTE STRONG
RADIATIONAL COOLING TONIGHT. CONDITIONS SHOULD BE IMPROVING WITH
REGARDS TO AVIATION OPERATIONS DURING THE NEXT 24 HOURS.

&&

.AIR STAGNATION...CLOUDS AND SHOWERS WILL BE DISSIPATING THIS
EVENING AS DRIER CANADIAN AIR MOVES INTO THE NORTHERN ROCKIES.
CLEARING SKIES AND CALM WINDS AT THE SURFACE WILL PROMOTE STRONG
RADIATIONAL COOLING TONIGHT AND AGAIN THURSDAY NIGHT. A RIDGE OF
HIGH PRESSURE WILL BE APPROACHING THE INTER-MOUNTAIN REGION FROM
THE WEST FURTHER STABILIZING THE LOWER ATMOSPHERE THROUGH THE
WEEKEND.

&&

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

$$

SHORT TERM...MSJ
LONG TERM....DICKERSON
AVIATION...DE ROSA