FXUS65 KMSO 012140
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
240 PM MST TUE DEC 1 2009

...COLDER CONDITIONS EXPECTED FOR THE WEEKEND...

.DISCUSSION...

TONIGHT THROUGH THURSDAY...COOL AND DRY NORTHERLY FLOW ALOFT WILL BE 
PRESENT OVER WESTERN MONTANA AND NORTH CENTRAL IDAHO DURING THE 
SHORT TERM FORECAST PERIODS. AREAS OF SNOW THAT DEVELOPED OVER THE 
REGION THIS MORNING HAVE MOVED SOUTH AND EAST INTO SOUTHWEST MONTANA. 
MOUNTAIN SNOW IS ANTICIPATED TO LINGER THROUGH THE EARLY EVENING 
HOURS IN THE VICINITY OF BUTTE AND LOST TRAIL PASS...WITH FAST 
DISSIPATING CLOUDINESS THEREAFTER. A SURFACE PRESSURE GRADIENT ALONG 
THE CONTINENTAL DIVIDE...PARTLY RESPONSIBLE FOR THE INTRODUCTION OF 
COLD AIR TODAY...WILL WEAKEN DURING THE EVENING AS WELL. MOST VALLEY 
LOCATIONS WEST OF THE CONTINENTAL DIVIDE WILL EXPERIENCE CALM 
WINDS...WITH RAPID RADITIONAL COOLING AFTER SUNSET. CONSIDERING 
RAPID LOW LEVEL DRYING DURING THIS AFTERNOON...THE CONFIDENCE IN FOG 
DEVELOPMENT IS HIGHEST IN THE FOG PRONE VALLEYS OF NORTHWEST MONTANA 
AND NORTH CENTRAL IDAHO. THE PERSISTENT NORTHERLY FLOW ALOFT WILL 
MAINTAIN THE RELATIVELY COOL AIR AND MOSTLY CLEAR SKIES OVER THE 
REGION THROUGH THURSDAY...WITH OVERNIGHT TEMPERATURES FALLING BELOW 
ZERO DEGREES IN VALLEYS JUST WEST OF THE CONTINENTAL DIVIDE. 

THURSDAY NIGHT THROUGH THE WEEKEND...THE MODELS HAVE FINALLY COME
IN AGREEMENT WITH THE DISTURBANCE MOVING THROUGH THE NORTHERN
ROCKIES FOR THE END OF THE WEEK. THE CURRENT RUNS INDICATE THAT
THE FEATURE WILL MOVE FROM NORTH THROUGH SOUTH STARTING LATE
FRIDAY AFTERNOON THROUGH OUT THE NIGHT. THE MODELS ARE STILL IN
CONSESUS WITH THE BROAD TROUGH SETTLING OVER THE PACIFIC
NORTHWEST. THIS TROUGH IS STILL EXPECTED TO ALLOW AN ARCTIC
AIRMASS TO ENCROACH THE REGION. TEMPERATURES BY SUNDAY AND MONDAY
COULD BE AS MUCH AS 15 TO 20 DEGREES BELOW SEASON
NORMALS...ESPECIALLY ALONG THE CONTINENTAL DIVIDE.

&&

.AVIATION...
MOSTLY CLEAR SKIES WILL DEVELOP ACROSS THE REGION BY 02/0300Z IN
THE PRESENCE OF DRY NORTHERLY FLOW ALOFT DURING THE NEXT 24 HOURS.
THROUGH 02/0300Z...OCCASIONAL TERRAIN OBSCURATIONS WILL BE FOUND
NEAR KBTM AND KSMN DUE TO SNOW ALONG HIGHER TERRAIN.
OTHERWISE...FEW AVIATION IMPACTS ARE ANTICIPATED DURING THIS TIME.

&&

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

$$

SHORT TERM...ZUMPFE
LONG TERM....SMITH
AVIATION...ZUMPFE