FXUS65 KMSO 151101
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
401 AM MST TUE DEC 15 2009

.DISCUSSION...A WARM PACIFIC WEATHER SYSTEM IS CURRENTLY SPREADING
WIDESPREAD PRECIPITATION ACROSS THE PACIFIC NORTHWEST AND WILL
MOVE INTO NORTH CENTRAL IDAHO AND WESTERN MONTANA EARLY THIS
MORNING. CURRENT ADVISORIES LOOK IN GOOD SHAPE WITH NO CHANGES
EXPECTED. WILL CONTINUE TO MONITOR THE MISSOULA AND BITTERROOT
VALLEY TODAY AS AT THIS TIME...IT LOOKS LESS LIKELY THE MISSOULA
VALLEY WILL SEE FULL MIXING TODAY AND SNOW IS EXPECTED TO BE THE
DOMINANT PRECIPITATION TYPE TODAY. COULD SEE UP TO 3 INCHES OF
ACCUMULATION IF WE FAIL TO MIX. THE BITTERROOT VALLEY HOWEVER HAS
ALREADY EXPERIENCED MIXING WITH HAMILTON ALREADY ABOVE FREEZING.
THEREFORE WHEN PRECIPITATION BEGINS THERE WILL BE A DEFINITE LINE
OF RAIN TO THE SOUTH WITH SNOW IN MISSOULA VALLEY. BETWEEN
FLORENCE AND STEVI...SNOW IS EXPECTED AT THE ONSET...THEN BECOME A
MIX OF RAIN AND SNOW. ONCE THE PRECIPITATION MOVES INTO WESTERN
MONTANA AND WE GET A BETTER IDEA OF THE AMOUNT OF MIXING TAKING
PLACE WITH THE PRECIPITATION A BETTER RAIN/SNOW LINE WILL BE
DETERMINED. MAY EVEN NEED SOME WINTER WEATHER ADVISORIES FOR THE
NORTHERN BITTERROOT VALLEY AND MISSOULA VALLEY LATER THIS MORNING. 

WITH THE ENTRANCE REGION OF THE JET OVER WESTERN MONTANA THIS
EVENING...EXPECT A BRIEF BREAK IN THE ACTION IN THE VALLEYS AS
WEST WINDS KICK IN AND RESULT IN DOWNSLOPING OVER THE WESTERN
MONTANA VALLEYS. THIS MAY ALSO RESULT IN ENOUGH CLEARING TO ALLOW
TEMPERATURES TO DROP BELOW FREEZING. WITH THE NEXT SLUG OF
MOISTURE MOVING IN AFTER MIDNIGHT ON A WARM PUSH OF AIR...THIS
WILL SET THE STAGE TO INTRODUCE SOME FREEZING RAIN LATE TONIGHT
AND EARLY WEDNESDAY MORNING. AGAIN...THIS SCENARIO IS HIGHLY
DEPENDENT ON WHAT HAPPENS WITH TEMPERATURES EARLY THIS EVENING.
HAVE KEPT MENTION OF FREEZING RAIN IN THE FORECAST AS A RESULT.
WEDNESDAY WILL REMAIN UNSTABLE WITH BETTER MIXING AND EXPECT ALL
BUT EXTREME NORTHWEST MONTANA VALLEYS TO MIX ABOVE FREEZING.
THEREFORE PRECIPITATION IS EXPECTED TO TRANSITION FROM A MIX IN
THE MORNING TO RAIN IN MOST OF THE LOWER VALLEYS OF NORTH CENTRAL
IDAHO AND WESTERN MONTANA BY WEDNESDAY AFTERNOON.

THURSDAY THROUGH MONDAY...WHILE MEDIUM RANGE MODELS ARE STARTING
TO ALIGN TO A SIMILAR SOLUTION FOR THE END OF THE WEEK...THERE
STILL IS UNCERTAINTY ABOUT THE GENERAL UPPER LEVEL PATTERN AND
MOISTURE FOR THE REMAINDER OF THE FORECAST PERIOD. PRECIPITATION
CHANCES BACK OFF TOWARDS THE END OF THE WEEK AS A SHORTWAVE RIDGE
BUILDS OVER THE NORTHWESTERN UNITED STATES. THE POTENTIAL FOR
AREAS OF FREEZING FOG ARE POSSIBLE THURSDAY EVENING INTO FRIDAY
UNDER THE STABLE HIGH PRESSURE RIDGE. SEEMS RIDGING MAXIMUM WILL BE
RELEASED SOMETIME FRIDAY BEFORE IT BEGINS TO FLATTEN AHEAD OF THE
NEXT PACIFIC WEATHER SYSTEM. WEST-NORTHWESTERLY FLOW WILL THEN BEGIN
TO SETTLE OVER THE AREA WITH EMBEDDED IMPULSES IN THE FLOW THAT
INCREASE PRECIPITATION CHANCES TO TREND WITH CLIMATOLOGY. BOTH THE
GFS AND ECMWF ARE STARTING TO HINT AT ANOTHER PACIFIC LOW PRESSURE
SYSTEM PUSHING NEAR THE NORTHWEST COAST AND SPREADING
PRECIPITATION INLAND INTO THE NORTHERN ROCKIES. FOR CURRENT
FORECAST PACKAGE...DID NOT MAKE SIGNIFICANT CHANGES TO
TEMPERATURES OR PRECIPITATION UNTIL A MORE UNIFORM SOLUTION IS
SETTLED ON.

&&

.AVIATION...A WARM PACIFIC FRONT MOVING THROUGH THE INTERMOUNTAIN
REGION WILL LOWER CEILINGS AND BRING WIDESPREAD PRECIPITATION TO
NORTH CENTRAL IDAHO AND WESTERN MONTANA TODAY. EXPECT TERRAIN
OBSCURATIONS AND LOWERED CEILINGS AND VISIBILITIES THROUGH 16/00Z.
A BRIEF BREAK THIS EVENING TO MANY VALLEYS...BUT ANOTHER WAVE OF
ENERGY/MOISTURE WILL SPREAD MORE PRECIPITATION ACROSS THE REGION
AFTER MIDNIGHT. 

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR
     KOOTENAI/CABINET REGION-LOWER CLARK FORK REGION.

     WINTER WEATHER ADVISORY FROM 8 AM THIS MORNING TO 8 PM MST THIS 
     EVENING FOR WEST GLACIER REGION.

ID...WINTER WEATHER ADVISORY UNTIL NOON PST TODAY FOR NORTHERN 
     CLEARWATER MOUNTAINS-OROFINO/GRANGEVILLE REGION-SOUTHERN 
     CLEARWATER MOUNTAINS.

&&

$$

SHORT TERM...MEAD
LONG TERM....NOLTE
AVIATION...MEAD