FXUS65 KMSO 050447
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
947 PM MST FRI DEC 4 2009

...SNOW ALONG THE CONTINENTAL DIVIDE TONIGHT AND SATURDAY FOLLOWED
BY INCREASING NORTHEAST WINDS AND BITTERLY COLD AIR INVADING THE
NORTHERN ROCKIES OVER THE WEEKEND...

.DISCUSSION...ONLY MADE SOME MINOR TWEEKS TO THE FORECAST FOR
OVERNIGHT. ADDED MENTION OF BLOWING SNOW OVER MARIAS AND MACDONALD
PASSES AS WELL AS THE HIGHER TERRAIN ALONG THE DIVIDE. ALSO
LOWERED FORECAST LOW TEMPERATURES IN THE HIGHER TERRAIN SINCE MOST
HIGH ELEVATION SENSORS ARE SHOWING COLDER AIR ALREADY IN PLACE.
THIS IS FURTHER SUPPORTED BY THE 00Z SPOKANE AND GREAT FALLS
SOUNDINGS WHICH DISPLAY SIGNIFICANT COOLING ABOVE THE SURFACE.
ALSO ADDED MENTION OF PATCHY FREEZING FOG AROUND
GRANGEVILLE...KAMIAH AND OROFINO GIVEN OBSERVATIONS ARE SHOWING
NEAR SATURATED CONDITIONS AND SPOTTER REPORTS CONFIRM THE PRESENCE
OF FREEZING FOG AND LIGHT SNOWFALL.

OTHERWISE THE FORECAST APPEARS TO BE ON TRACK FOR THE NEXT TWENTY-
FOUR HOURS.

&&

.AVIATION...A SYSTEM DROPPING IN FROM THE NORTH WILL BEGIN TO
SPREAD LIGHT SNOW OVER NORTHWEST MONTANA THIS AFTERNOON. THE SNOW
WILL SPREAD THROUGHOUT THE REMAINDER OF THE NORTHERN ROCKIES
OVERNIGHT AND SATURDAY. WIDESPREAD MVFR CEILINGS AND VISIBILITIES
ARE LIKELY...WITH LOCAL IFR POSSIBLE. BLOWING SNOW COULD FURTHER
REDUCE VISIBILITIES SATURDAY AFTERNOON AND EVENING.

&&

.PREV DISCUSSION... /ISSUED 149 PM MST FRI DEC 4 2009/ 

DISCUSSION...AN UPPER TROUGH THAT IS OVER THE CANADIAN ROCKIES
EARLY THIS AFTERNOON WILL MOVE OVER THE MONTANA ROCKIES LATER
TODAY. THIS WILL SPREAD PERSISTENT LIGHT SNOW ACROSS THE REGION.
AREAS NEAR THE NORTHERN CONTINENTAL DIVIDE FROM THE CANADIAN
BORDER THROUGH AROUND SEELEY LAKE ARE EXPECTED TO RECEIVE 3 TO 7
INCHES FROM THIS EVENING THROUGH SATURDAY. WITH THIS FEATURE
COMING FROM THE NORTH...SIGNIFICANT COLD AIR WILL ACCOMPANY AND
FOLLOW IT. THE FIRST IMPACT FROM THIS IS VERY HIGH SNOW TO WATER
RATIOS ON THE ORDER OF 20 OR 25 TO 1. THEREFORE THE SNOW WILL BE
VERY LIGHT AND POWDERY. THIS IS IMPORTANT BECAUSE THE INVADING
COLD AIR WILL CREATE INCREASING NORTHEAST WINDS...AND THEREFORE
BLOWING SNOW IS A CONCERN. AGAIN THIS WILL BE AN ISSUE MAINLY NEAR
THE DIVIDE...BUT COULD ALSO IMPACT THE KALISPELL AREA.

THE VERY COLD ARCTIC AIR MASS WILL CONTINUE TO SINK INTO WESTERN
MONTANA AND NORTH CENTRAL IDAHO THROUGH TUESDAY. AS IT DOES SO...A
SURFACE PRESSURE GRADIENT WILL BEGIN TO TIGHTEN AND CAUSE EAST-
NORTHEAST WINDS TO INCREASE THROUGHOUT THE DAY SATURDAY. BY
SATURDAY NIGHT...SUSTAINED WIND SPEEDS OF 15 TO 25 MPH WITH HIGHER
GUSTS APPROACHING 35 MPH WILL OCCUR...PARTICULARLY WHERE WIND IS
CHANNELED THROUGH GAPS ALONG THE CONTINENTAL DIVIDE. WINDS WILL
CONTINUE TO INCREASE OVERNIGHT AND THROUGH THE DAY SUNDAY. DAYTIME
HIGH TEMPERATURES WILL STRUGGLE TO GET OUT OF THE SINGLE DIGITS
FOR MOST LOCATIONS. WITH AIR THIS COLD RESIDING FIRMLY OVER THE
REGION...ANY WINDS THAT ARE GENERATED WILL CAUSE WIND CHILLS TO
STAY AT DANGEROUS VALUES. THE COLDEST WIND CHILLS WILL BE FELT
LATE SUNDAY THROUGH MONDAY MORNING AS EVEN COLDER AIR SETTLES INTO
THE REGION SUNDAY NIGHT. LOW TEMPERATURES WILL FALL INTO THE
NEGATIVE TEENS AND TWENTIES...WITH WIND CHILLS EXPECTED TO BE
ANYWHERE FROM -25 TO -40 DEGREES BY MONDAY MORNING.
 
BY MONDAY AFTERNOON THE PRESSURE GRADIENT WILL FINALLY WEAKEN AND
ALLOW WINDS TO DIE OFF. HOWEVER NO RELIEF IN THE WAY OF WARMER
TEMPERATURES IS EXPECTED. MONDAY NIGHT WILL BE YET ANOTHER
BITTERLY COLD NIGHT IN STORE FOR THE NORTHERN ROCKIES...IF NOT THE
COLDEST EXPECTED DURING THIS TIME FRAME. THIS WILL BE DUE TO
CLEARING SKIES MONDAY NIGHT WHICH WILL ONLY AID IN TEMPERATURES
DROPPING TO EXTREMELY COLD VALUES. TEMPERATURES ARE ANTICIPATED TO
RANGE FROM -10 TO -30 DEGREES BY TUESDAY MORNING.

THE REMAINDER OF NEXT WEEK WILL CONTINUE TO BE COLD AND
UNSETTLED...WITH PERIODS OF SNOW.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WIND CHILL WARNING FROM 8 PM SATURDAY 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 SATURDAY 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 SATURDAY FOR 
     POTOMAC/SEELEY LAKE REGION-WEST GLACIER REGION.

ID...NONE.
&&

$$

UPDATE...DICKERSON
PREVIOUS DISCUSSION...WHITMORE/ALLEGRETTO/DE ROSA
AVIATION...PALLISTER