FXUS65 KMSO 072136
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
236 PM MST MON DEC 7 2009

...BITTERLY COLD TONIGHT...

.DISCUSSION...THE PEAK COLD SHOULD BE REALIZED TONIGHT. CLEAR
SKIES COMBINED WITH LIGHT WINDS MOST AREAS AND A COLD UPPER TROUGH
OF LOW PRESSURE SHOULD SUPPORT NEAR IDEAL RADIATIONAL COOLING
TONIGHT. HOWEVER...SOME EASTERLY FLOW WILL CONTINUE IN THE EAST TO
WEST VALLEYS CREATING LOCAL AREAS OF DANGEROUSLY LOW WIND CHILLS
TONIGHT. TEMPERATURES WILL STRUGGLE TO WARM TUESDAY UNDER THE VERY
SHORT DECEMBER DAY AND LOW SUN ANGLE.

WEDNESDAY THROUGH FRIDAY THE INTER-MOUNTAIN REGION WILL REMAIN IN
A NORTHERLY UPPER LEVEL FLOW. STILL ANTICIPATE SOME UPPER LEVEL
WAVES AND MOISTURE TO MOVE THROUGH THIS FLOW...WITH THE BEST
POTENTIAL FOR STEADY LIGHT SNOW WEDNESDAY/WEDNESDAY NIGHT AS AN
UPPER LEVEL JET WILL ADD SOME LIFT SUPPORT. AGAIN...IT WILL BE
LITTLE TO NO ACCUMULATION BUT STEADY SNOW THROUGH THIS PERIOD.
THURSDAY NIGHT THROUGH FRIDAY THE UPPER FLOW WILL TRANSITION TO
MORE NORTHWEST/WEST AS THE PARENT CANADIAN LOW MOVES CLOSER TO THE
US BORDER. THIS WILL ADJUST THE BEST LOCATION FOR SNOW
NORTH...MAINLY ALONG THE CANADIAN BORDER AND GLACIER NATIONAL
PARK. THIS WILL BE THE TIME FRAME MOST OPTIMUM FOR MODERATING
TEMPERATURES...BUT STILL WELL BELOW SEASONAL READINGS. FRIDAY
NIGHT MOISTURE WILL BEGIN TO MOVE IN FROM THE WEST AS A PACIFIC
WEATHER SYSTEM APPROACHES THE COAST. IN ADDITION...ANOTHER SURGE
OF ARCTIC AIR LOOKS TO BUILD UP EAST OF THE CONTINENTAL
DIVIDE...INCREASING EAST WINDS AND COOLING TEMPERATURES ALONG THE
DIVIDE.

SATURDAY THROUGH MONDAY...THE HYDROMETEOROLOGICAL PREDICTION
CENTER AND ENSEMBLE MEANS ARE LEANING TOWARD THE ECMWF MODEL
SOLUTION IN THE FAR EXTENDED AND HAVE BEGUN TO TREND THE FORECAST
IN THIS DIRECTION. SATURDAY COULD BE A TRICKY FORECAST FOR TWO
REASONS. FIRST...MOISTURE AND ENERGY FROM A CANADIAN LOW TRACKING
TOWARD SOUTHERN HUDSON BAY SHOULD EJECT OVER THE NORTHERN
ROCKIES...PULLING COOLER ARCTIC AIR INTO NORTHWEST MONTANA AND
INCREASING EASTERLY WINDS LATE SATURDAY. SECOND...A PACIFIC SYSTEM
SHOULD MOVE ONSHORE AND BEGIN TO DIG SOUTHWARD INTO THE GREAT
BASIN. AS THE PACIFIC SYSTEM MOVES INLAND...A SUBSTANTIAL INCREASE
IN MOISTURE SHOULD OVERRUN THE COOLER AIR AT THE SURFACE AND BRING
STRATIFORM SNOW TO THE NORTHERN ROCKIES. SO THE INTERACTION OF THE
CANADIAN LOW AND PACIFIC LOW IS WHAT WILL MAKE THE FORECAST
DIFFICULT AS THIS SCENARIO COMES TO FRUITION. IN ADDITION...A LOW
PRESSURE SYSTEM DROPPING SOUTH FROM BRITISH COLUMBIA ON MONDAY
SHOULD REINFORCE THE COLDER AIR ALREADY IN PLACE AND KEEP SNOW
OVER THE AREA INTO EARLY NEXT WEEK.

&&

.AVIATION...A VERY COLD AND DRY AIR MASS WILL CONTINUE TONIGHT
INTO TUESDAY. HOWEVER...NEAR OPEN BODIES OF WATER...SUCH AS
FLATHEAD LAKE...SOME LOW STRATUS FORMATION IS LIKELY OVERNIGHT.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WIND CHILL WARNING FROM 6 PM THIS EVENING TO 5 AM MST TUESDAY 
     FOR MISSOULA/BITTERROOT VALLEYS.

ID...NONE.
&&

$$

SHORT TERM...BAUCK
LONG TERM....MEAD/DE ROSA
AVIATION...BAUCK