FXUS65 KMSO 222135
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
235 PM MST TUE DEC 22 2009

.DISCUSSION...SNOW SHOWERS ARE BEGINNING TO DECREASE AS AN
ASSOCIATED LOW PRESSURE SYSTEM SAGS SOUTH INTO THE GREAT BASIN.
HOWEVER...NOT MUCH OF A BREAK IS ANTICIPATED AS ANOTHER WEATHER
SYSTEM DEVELOPS OVER SOUTHWEST CANADA AND BEGINS TO SPREAD SNOW
INTO WESTERN MONTANA AND PORTIONS OF NORTH-CENTRAL IDAHO LATER
TONIGHT. WEST GLACIER AND SEELEY-SWAN REGIONS WILL BE THE PRIMARY
TARGET AS THIS SYSTEM SLIDES SOUTH ALONG THE CONTINENTAL DIVIDE.
WINTER WEATHER ADVISORIES ARE IN EFFECT FOR THESE AREAS VALID
LATER TONIGHT THROUGH WEDNESDAY MORNING. LIGHT SNOW CAN ALSO BE
EXPECTED ELSEWHERE WITH MINOR ACCUMULATIONS. THIS SAME CANADIAN
SYSTEM WILL ALSO DRAG A MUCH COOLER AIR MASS INTO THE NORTHERN
ROCKIES WEDNESDAY AND WEDNESDAY NIGHT. THERE MAY BE A BRIEF
EPISODE OF SNOW BANDING WEDNESDAY...OTHERWISE SNOW IS EXPECTED TO
TAPER OFF WEDNESDAY AFTERNOON AS COLD..DRIER AIR MAKES ITS WAY
SOUTH. CLEARING SKIES WITH LIGHT WINDS (PLUS SNOW ON THE
GROUND) WOULD PROMOTE STRONG RADIATIONAL COOLING WEDNESDAY NIGHT
AND MUCH COLDER NIGHTTIME LOWS.

A DRY NORTHERLY FLOW IS EXPECTED THURSDAY. A RIDGE OF HIGH
PRESSURE WILL SLOWLY SHIFT EASTWARD OVER THE NORTHERN ROCKIES
FRIDAY THROUGH THE WEEKEND. COLD AIR THAT WILL MOVE SOUTHWARD OVER
THE REGION WEDNESDAY AND THURSDAY WILL BECOME LOCKED IN THE
VALLEYS AS THE RIDGE OF HIGH PRESSURE SHIFTS OVER THE REGION. IN
FACT...THERE MAY BE A NET COOLING IN THE VALLEYS FRIDAY AND
SATURDAY WITH THE LONG NIGHTS ALLOWING EVEN MORE HEAT TO ESCAPE.
AS THE LOWER ATMOSPHERE BECOMES QUITE STABLE FRIDAY THROUGH THE
WEEKEND...INCREASING VALLEY FREEZING FOG AND LOW CLOUDS CAN BE
EXPECTED. THE FREEZING FOG/STRATUS SHOULD FIRST DEVELOP NEAR THE
LARGER RESERVOIRS AND FLATHEAD LAKE...BUT BY THE WEEKEND EXPAND TO
OTHER VALLEYS AS WELL. IN THE LONGER TERM...A SPLIT FLOW AND
RESULTANT GENERALLY DRY CONDITIONS IS EXPECTED TO PERSIST ON THE
WEST COAST INTO EARLY NEXT WEEK.

&&

.AVIATION...A MOIST ATMOSPHERE WILL PERSIST THROUGH THIS EVENING
WITH MUCH OF THE TERRAIN CONTINUING TO BE OBSCURED. A WEATHER
DISTURBANCE WILL BRUSH THE AREA WEDNESDAY AND PRODUCE SCATTERED
AREAS OF LIGHT SNOW WITH TERRAIN OBSCURATIONS AND LOCALLY LOW
VISIBILITIES IN VALLEYS AS WELL.  

&&

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

     WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 11 AM MST 
     WEDNESDAY FOR POTOMAC/SEELEY LAKE REGION.

ID...NONE.
&&

$$

SHORT TERM...MSJ
LONG TERM....BAUCK
AVIATION...BAUCK