FXUS65 KMSO 111058
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
358 AM MST FRI DEC 11 2009

...SIGNIFICANT SNOW POSSIBLE THIS WEEKEND...ESPECIALLY OVER NORTH
CENTRAL IDAHO AND NORTHWEST MONTANA...

.DISCUSSION...TODAY AND TONIGHT WILL BE QUITE TRANQUIL SINCE THE
REGION FALLS IN BETWEEN TWO APPROACHING STORM SYSTEMS SET FOR
COLLISION THIS WEEKEND. EXPECT A SLIGHT MODERATION IN BOTH HIGH
AND LOW TEMPERATURES WHICH WILL BE HEAVILY DEPENDENT UPON CLOUD
COVER.

SATURDAY THROUGH TUESDAY...THE NEXT WEATHER SYSTEM IS EXPECTED TO 
OVERTAKE THE NORTHERN ROCKIES THIS WEEKEND. THE BIG STORY WILL BE
THE EVOLUTION OF A CANADIAN LOW PRESSURE SYSTEM DRAWING COLD
ARCTIC AIR SOUTH OUT OF CANADA INTERACTING WITH A WARM PACIFIC
LOW PRESSURE TROUGH WITH A SUBTROPICAL MOISTURE CONNECTION. THE
INITIAL WARM FRONT LOOKS TO PASS THROUGH THE REGION ON SATURDAY
BRINGING THE FIRST WAVE OF SNOW TO NORTH CENTRAL IDAHO AND WESTERN
MONTANA BEFORE STALLING. THE MAIN QUESTIONS WITH THIS SYSTEM HAVE
BEEN WHERE THE WARM FRONT WILL STALL AND IF THE CANADIAN ARCTIC
FRONT WILL PUSH WEST OF THE DIVIDE LATE SATURDAY TO SUNDAY. THERE
HAS BEEN A LOT OF DISCREPANCY AS TO WHETHER OR NOT THE ARCTIC FRONT
WILL MAKE ITS WAY INTO WESTERN MONTANA...BUT RECENTLY GUIDANCE HAS
COME INTO BETTER AGREEMENT WITH THE ARCTIC FRONT PUSHING OVER THE
DIVIDE ON SATURDAY NIGHT. THESE TWO FRONTAL BOUNDARIES WILL BE
BIG PLAYERS AS TO HOW MUCH SNOW WILL FALL AND WHAT LOCATIONS ARE
MOST IMPACTED. THE BEST POTENTIAL FOR MODERATE TO HEAVY SNOW
REMAINS OVER THE CLEARWATER/BITTERROOT MOUNTAINS...LOLO
PASS...LOOKOUT PASS...GLACIER PARK...AND THE SEELEY/SWAN REGION.
IMPORTANT FACTORS FOR DETERMINING HEAVY SNOWFALL OUTSIDE OF THESE
REGIONS...INCLUDING THE TRACK OF THE SURFACE LOW AND HOW FAR SOUTH
THE ARCTIC BOUNDARY WILL TRAVEL...ARE STILL IN QUESTION AT THIS
TIME. SO CONFIDENCE IS NOT AS HIGH FOR SIGNIFICANT SNOW ACCUMULATIONS
ACROSS THE REST OF THE AREA AT CURRENT TIME.

HOWEVER... A WINTER STORM WATCH HAS BEEN ISSUED FOR THE AFOREMENTIONED
LOCATIONS AND A HAZARDOUS WEATHER OUTLOOK WILL BE INCLUDED FOR THE
LOCATIONS WITH THE POTENTIAL FOR HEAVY SNOW BUT WITH LESS
CONFIDENCE SUCH AS THE MISSOULA/BITTERROOT VALLEYS...FLATHEAD/MISSION
VALLEYS...SAPPHIRE MOUNTAINS AND CAMAS PRAIRIE/GRANGEVILLE REGION
IN IDAHO. ALL IN ALL THIS IS SHAPING UP TO LIKELY BE THE BIGGEST
WINTER STORM OF THE SEASON AS FAR AS SNOWFALL GOES.

THERE CONTINUES TO BE A GREAT DEAL OF SPREAD BETWEEN LONGER RANGE
FORECAST MODEL SOLUTIONS (GFS/ECMWF/CANADIAN) AS WELL AS THE
INDIVIDUAL ENSEMBLE MEMBER FORECASTS OF THE GEFS AND ECMWF FROM
TUESDAY ONWARD. IN GENERAL...THESE MODELS ARE HAVING A DIFFICULT TIME
DETERMINING WEATHER AN AMPLIFIED RIDGE WILL DEVELOP NEXT WEEK...
BRINGING A BREAK IN THE CHANCES FOR PRECIPITATION OR A BROAD...
FLATTER RIDGE OF HIGH PRESSURE THAT WOULD BRING A CONTINUED CHANCE
FOR PRECIPITATION AND GRADUALLY MODERATING TEMPERATURES. AFTER
CAREFUL ANALYSIS OF THE MODELS HAVE CONTINUED TO TREND THE FORECAST
TOWARDS A FLATTER RIDGING SOLUTION WITH NEAR CLIMATOLOGICAL CHANCES
FOR PRECIPITATION AND SEASONAL TEMPERATURES. THIS APPEARS TO BE THE
MOST REALISTIC SOLUTION WHILE ALSO GARNERING SUPPORT FROM THE
HYDRO-METEOROLOGICAL PREDICTION CENTER.

&&

.AVIATION...DECENT FLYING CONDITIONS WILL BE PRESENT TODAY WHILE
THE NORTHERN ROCKIES REGION FALLS IN BETWEEN TWO APPROACHING
WEATHER SYSTEMS. CLOUDS WILL INCREASE LATE IN THE DAY WHICH WILL
LIKELY OBSCURE HIGHER TERRAIN OVER NORTHWEST MONTANA. THE
POTENTIAL FOR SNOWFALL WILL INCREASE THROUGH THE DAY ON SATURDAY.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SUNDAY EVENING 
     FOR LOWER CLARK FORK REGION.

     WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SUNDAY EVENING 
     FOR POTOMAC/SEELEY LAKE REGION-WEST GLACIER REGION.

ID...WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SUNDAY EVENING 
     FOR NORTHERN CLEARWATER MOUNTAINS-SOUTHERN CLEARWATER 
     MOUNTAINS.

&&

$$

SHORT TERM...DICKERSON/KITSMILLER
LONG TERM....DICKERSON 
AVIATION...DICKERSON