FXUS65 KMSO 290250
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
750 PM MST SAT NOV 28 2009

.UPDATE...ADDED FREEZING DRIZZLE TO FLATHEAD AREA TO CURRENT
FORECAST FOR THIS EVENING.

&&

.DISCUSSION...FREEZING DRIZZLE HAS BEEN REPORTED IN THE KALISPELL
AND COLUMBIA FALLS AREAS THIS EVENING IN THE FLATHEAD VALLEY. IT
SHOULD BE SHORT-LIVED AS INFRARED IMAGERY IS INDICATING THAT
PRECIPITATION SHOULD BE WANING OVER THE REMAINDER OF THE EVENING
AS PREVIOUSLY FORECASTED.

&&

.AVIATION...SNOW SHOWERS AND LIGHT FREEZING DRIZZLE AT KGPI ARE
EXPECTED TO KEEP LOW CEILINGS AND REDUCED VISIBILITIES AT THE
AIRPORT THROUGH THIS EVENING BEFORE THE ATMOSPHERE
STABILIZES...CAUSING SHOWERS TO GRADUALLY DIMINISH. FOG
DEVELOPMENT IN THE VICINITY OF KGPI IS ALSO POSSIBLE BY SUNDAY
MORNING BUT WILL BE HIGHLY DEPENDENT ON CEILINGS BREAKING OUT OR
RISING. OVERALL NORTHWEST FLOW WILL CONTINUE THE THREAT FOR
MOUNTAIN SNOW SHOWERS ACROSS THE NORTHERN ROCKIES THROUGH SUNDAY.
MOUNTAINS AND PASSES MAY BE OBSCURED AT TIMES THROUGH SUNDAY
ACROSS THE REGION.

&&

.PREV DISCUSSION... /ISSUED 519 PM MST SAT NOV 28 2009/ 

UPDATE...INCREASED POPS IN FLATHEAD VALLEY AND GLACIER PARK AREAS
THIS EVENING.

DISCUSSION...SNOW SHOWERS CONTINUE TO PLAGUE THE NORTHERN
FLATHEAD VALLEY AND GLACIER PARK AREAS AT THIS HOUR. SHOWERS ARE A
RESULT OF NORTHWEST FLOW STREAMING MOISTURE DOWN FROM A
DISTURBANCE IN BRITISH COLUMBIA. SHOWERS SHOULD GRADUALLY TAPER
OFF THROUGH THE EVENING AS THE ATMOSPHERE STABILIZES. SOME
ENHANCEMENT ON INFRARED IMAGERY OVER THE NORTHERN CLEARWATERS OF
IDAHO HAS ALSO PROMPTED AN INCREASE TO POPS IN THIS REGION FOR THE
EVENING AS WELL. WILL MONITOR THIS AREA TO SEE IF ANY FURTHER
UPDATES WILL BE NECESSARY.

PREV DISCUSSION... /ISSUED 247 PM MST SAT NOV 28 2009/ 

DISCUSSION...

TONIGHT THROUGH MONDAY...NORTHWESTERLY FLOW ALOFT WILL CONTINUE TO 
BE PRESENT OVER NORTH CENTRAL IDAHO AND WESTERN MONTANA THROUGH 
MIDDAY MONDAY. A PORTION OF THE PACIFIC JET STREAM ACCOMPANIES THIS 
FLOW REGIME AND WILL BE RESPONSIBLE FOR AREAS OF SNOW DEVELOPING
THROUGHOUT MUCH OF THE NEAR TERM. MOST OF THE SNOW WILL BE
CONFINED TO BENEATH THE CORE OF THE JET OVER NORTHWEST MONTANA.
LITTLE SNOW ACCUMULATION IS ANTICIPATED WITH THESE FEATURES
PRESENT...HOWEVER EVEN A LIGHT DUSTING OF SNOW COULD CAUSE AREA
ROADS TO BECOME HAZARDOUSLY ICY. FOR MUCH OF THE FORECAST
PERIOD...SNOW WILL BE LOCKED TO THE HIGH TERRAIN. MEANWHILE...HIGH
PRESSURE WILL BE STRENGTHENING OVER THE PACIFIC NORTHWEST. WITH
THE EXCEPTION OF NORTHWEST MONTANA...TEMPERATURES WILL BE ON THE
INCREASE OVER HIGH TERRAIN. GIVEN THE LOW SUN ANGLE BY THIS TIME
OF YEAR AND WEAK LOW LEVEL WINDS...TEMPERATURE INVERSIONS ARE
EXPECTED TO DEVELOP WITHIN MANY AREA VALLEYS. THIS PARTICULAR
PATTERN WILL BE CONDUCIVE FOR FOG DEVELOPMENT BY SUNDAY OVERNIGHT
INTO MONDAY...FAVORING THE TYPICAL FOG PRONE VALLEYS IN NORTHWEST
MONTANA AND NORTH CENTRAL IDAHO.

A SIGNIFICANT LOW PRESSURE SYSTEM WILL MOVE ACROSS SOUTHERN CANADA
MONDAY NIGHT INTO TUESDAY CAUSING A COLD FRONT TO DRAG THROUGH THE
NORTHERN ROCKIES. THIS FRONT SHOULD INCREASE SHOWER POTENTIAL PLUS
INTRODUCE A COLDER AIR MASS TO THE AREA. AFTER THE PASSAGE OF THE
SYSTEM A RIDGE OF HIGH PRESSURE WILL BUILD OVER THE WEST COAST
LEAVING THE REGION UNDER NORTHWESTERLY FLOW. THIS FLOW PATTERN
COULD KEEP A FEW OROGRAPHIC SHOWERS GOING THROUGH WEDNESDAY. AFTER
WEDNESDAY NIGHT THE MODELS DIVERGE CONSIDERABLY...SO LITTLE
CONFIDENCE IS HELD THROUGH THE LATER PART OF THE WEEK. THE
GENERAL CONSENSUS IS A LOW PRESSURE SYSTEM WILL SWING THROUGH THE
REGION SOMETIME BETWEEN THURSDAY AND SATURDAY...BUT THERE ARE A WIDE
VARIETY SOLUTIONS ON TIMING. SO AT THIS TIME MADE LITTLE CHANGES
TO THE GOING FORECAST.

&&

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

$$

UPDATES...DEROSA
PREVIOUS DISCUSSION...ZUMPFE/SMITH
AVIATION...DEROSA