FXUS65 KMSO 142308
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
408 PM MST MON DEC 14 2009

.DISCUSSION...EXPECT ENOUGH WARM ADVECTION SNOW OVER THE NORTHERN
BITTERROOTS AND INTO THE KOOTENAI-CABINET REGION LATE TONIGHT AND
TUESDAY FOR A SNOW ADVISORY. VALLEYS WILL LIKELY SEE 2 TO 5 INCHES
WITH 4 TO 8 INCHES OR SO IN THE MOUNTAINS.

&&

AVIATION...A MOIST NORTHWEST FLOW WILL CONTINUE EARLY THIS
EVENING WITH WIDESPREAD MOUNTAIN OBSCURATIONS AND LOCAL LOW
VISIBILITIES IN THE VALLEYS IN THE VICINITY OF SHOWERS. A WARM
FRONT WILL PUSH A SIGNIFICANT SURGE OF PACIFIC MOISTURE ACROSS THE
REGION LATE TONIGHT AND TUESDAY WITH WIDESPREAD MOUNTAIN
OBSCURATIONS AND PRECIPITATION. 

&&

.PREV DISCUSSION... /ISSUED 248 PM MST MON DEC 14 2009/ 

DISCUSSION...THE MOIST NORTHWEST FLOW WILL QUICKLY DIMINISH THIS
EVENING IN ADVANCE OF AN APPROACHING WARM FRONT. THE WARM FRONT
SHOULD BEGIN TO SPREAD SIGNIFICANT MOISTURE AND ENERGY INTO
NORTH CENTRAL IDAHO FROM OROFINO TO PIERCE AFTER MIDNIGHT AND THEN
OVER NORTHWEST MONTANA AND THE BITTERROOTS TOWARD MORNING.

THE COLD AIR TRAPPED IN THE VALLEYS WILL MAKE THE TYPE OF
PRECIPITATION MOVING INTO THE REGION QUESTIONABLE. INITIALLY ALL
SNOW IS EXPECTED TONIGHT WITH ENOUGH ACCUMULATING TO WARRANT AN
ADVISORY ACROSS CENTRAL IDAHO ALL THE WAY TO THE OROFINO AREA. AS
THE WARMER AIR MOVES IN...THE SNOW WILL TURN TO RAIN IN THE LOWER
ELEVATIONS WHICH WILL CREATE SLICK ROADS ACROSS MUCH OF THE
AREA. THE WARM AIR WILL NOT LIKELY HAVE AS MUCH OF AN EFFECT NORTH
OF MISSOULA WHICH WILL KEEP MOSTLY SNOW IN THE FORECAST FOR THESE
LOCATIONS THROUGH TUESDAY. THE GLACIER PARK AREA WILL SEE SOME
GOOD TERRAIN-ENHANCED SNOWFALL WHICH WILL BE ENOUGH FOR AN
ADVISORY TUESDAY AFTERNOON THROUGH TUESDAY EVENING.

WEDNESDAY THROUGH SUNDAY...ANOTHER WEATHER DISTURBANCE AND SURGE
OF PACIFIC MOISTURE WILL MOVE ACROSS THE REGION WEDNESDAY. WITH
SOME COLD GROUND SURFACES AND COLD AIR TRAPPED IN VALLEYS...THE
PRECIPITATION MAY START OUT AS FREEZING RAIN IN SOME AREAS. ENOUGH
COLD AIR WILL CONTINUE ALOFT TO SUPPORT SNOW DOWN TO MOST PASS
LEVELS WITH SIGNIFICANT SNOW POSSIBLE WEDNESDAY. TEMPERATURES
SHOULD CONTINUE TO SLOWLY MODERATE IN THE VALLEYS INTO THURSDAY.
YET ANOTHER WEATHER DISTURBANCE SHOULD IMPACT THE AREA THURSDAY.
THE MODEL GUIDANCE BEGINS TO DIVERGE SOMEWHAT FRIDAY THROUGH
SUNDAY. AT THIS POINT THE MORE AMPLIFIED RIDGE OF HIGH PRESSURE IN
THE ECMWF SOLUTION IS PREFERRED FRIDAY AND SATURDAY. BEYOND
SATURDAY THE FORECAST BECOMES EVEN MORE UNCERTAIN DUE TO CONTINUED
MODEL FORECAST DIFFERENCES. 

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 5 PM MST 
     TUESDAY FOR KOOTENAI/CABINET REGION-LOWER CLARK FORK REGION.

     WINTER WEATHER ADVISORY FROM 8 AM TO 8 PM MST TUESDAY FOR WEST 
     GLACIER REGION.

ID...WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO NOON PST 
     TUESDAY FOR NORTHERN CLEARWATER MOUNTAINS-
     OROFINO/GRANGEVILLE REGION-SOUTHERN CLEARWATER MOUNTAINS.

&&

$$

UPDATE...WHITMORE
PREVIOUS DISCUSSION...BAUCK/LOEFFELBEIN
AVIATION...BAUCK