FXUS65 KMSO 082052
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
152 PM MST TUE DEC 8 2009

...CONTINUED VERY COLD TEMPERATURES TONIGHT...

.DISCUSSION...THE VERY COLD AIR MASS WILL REMAIN OVER THE NORTHERN
ROCKIES TONIGHT WITH CONTINUED NORTHERLY FLOW ALOFT. SOME CLOUD
COVER IS EXPECTED TO MOVE OVER FAR NORTHWEST MONTANA TOWARD
MORNING...AND THIS SHOULD PREVENT TEMPERATURES FROM DROPPING AS
LOW AS LAST NIGHT. AN EMBEDDED WEAK DISTURBANCE WILL MOVE OVERHEAD
DURING THE DAY WEDNESDAY...SPREADING CLOUDS AND A THREAT OF LIGHT
SNOW THROUGHOUT THE REGION. THIS WILL BE THE BEGINNING OF A
PERSISTENT MOIST NORTHWEST FLOW WITH WEAK MID AND UPPER LEVEL LIFT
DUE TO AN UPPER JET OVERHEAD. THERE WILL ALSO BE LIFT IN THE LOWER
ATMOSPHERE DUE TO MODERATE NORTHWEST WINDS RIDING OVER THE
TERRAIN. THIS PATTERN WILL HOLD THROUGH THE END OF THE WEEK. THIS
WILL SLOWLY MODIFY THE TEMPERATURE OF THE AIR MASS BY CLOUD COVER
AT NIGHT AND SOME WARMING OF THE FLOW AS IT BECOMES MORE
NORTHWEST. HOWEVER...IT WILL REMAIN COOLER THAN NORMAL FOR THIS TIME
OF YEAR THROUGH FRIDAY.

SATURDAY THROUGH SUNDAY...LATEST MODEL RUN OF THE ECMWF IS
BEGINNING TO DIG THE PACIFIC LOW FURTHER SOUTH SATURDAY AND
SUNDAY. THE LOW COULD REMAIN JUST ENOUGH TO THE NORTH TO PRODUCE
SNOW OVER THE SOUTHERN HALF OF THE NORTHERN ROCKIES. DURING THE
SAME TIMEFRAME...A CANADIAN SHORTWAVE FEATURE AND ASSOCIATED JET
IS EXPECTED TO DROP DOWN INTO NORTHWEST MONTANA. THIS FEATURE
SHOULD BRING ANOTHER ROUND OF ARCTIC AIR...ALBEIT MUCH WARMER THAN
THE LAST BLAST EARLIER IN THE WEEK...INTO THIS AREA. BOTH THE
PACIFIC SYSTEM AND THE CANADIAN SYSTEM HAVE THE POTENTIAL FOR
PRODUCING HEAVY SNOW OVER THE REGION...HOWEVER THE SMALLER
FEATURES LIKE WARM FRONTS AND SURFACE BOUNDARY LOCATIONS ARE
KEEPING A BIT OF UNCERTAINTY IN HOW THIS SCENARIO WILL PLAY OUT BY
THE WEEKEND. PLEASE REFERENCE WWW.WEATHER.GOV/MISSOULA FOR FURTHER
UPDATES REGARDING THE SYSTEM THIS WEEKEND.

MONDAY THROUGH TUESDAY...BOTH LOW PRESSURE SYSTEMS FROM THE
WEEKEND SHOULD EXIT TO THE EAST BY MONDAY KEEPING SNOW SHOWERS
ACROSS THE REGION UNDER NORTHWEST FLOW. ANOTHER MOIST PACIFIC
SYSTEM WILL BEGIN TO APPROACH THE NORTHERN ROCKIES TUESDAY. THIS
SYSTEM SHOULD USHER IN A WARMER AIR MASS WITH TEMPERATURES
POTENTIALLY REACHING VALUES SLIGHTLY ABOVE SEASONAL NORMALS.

&&

.AVIATION...BITTERLY COLD ARCTIC AIR WILL REMAIN OVER THE REGION
INTO WEDNESDAY. SKIES WILL REMAIN MOSTLY CLEAR OVERNIGHT...WITH
LIGHT WINDS. CLOUDS WILL BE INCREASING DURING THE DAY WEDNESDAY
WITH LIGHT SNOW MOVING IN FROM THE NORTHWEST AS A WEAK DISTURBANCE
MOVES OUT OF CANADA.

&&

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

$$

SHORT TERM...WHITMORE
LONG TERM....DEROSA
AVIATION...KOLATA