FXUS65 KMSO 252122
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
222 PM MST FRI DEC 25 2009

.DISCUSSION...MOST VALLEYS ACROSS NORTHWEST MONTANA AND AS FAR
SOUTH AS THE MISSOULA VALLEY. A PARTICULARLY CHALLENGING FORECAST
AHEAD FOR THE NEXT FEW PERIODS WITH RESPECT TO CLOUDS AND
TEMPERATURES. WHERE CLOUDS HANG AROUND THROUGH THE NIGHT AND INTO 
SATURDAY...TEMPERATURES WILL NOT SEE MUCH OF A DIURNAL RANGE. IN
CONTRAST...WHERE CLOUDS DISSIPATE THEN TEMPERATURES WILL COOL
MUCH MORE OVERNIGHT. WILL POINT THE FORECAST IN THE DIRECTION OF
HOLDING ONTO CLOUDS THROUGH THE NIGHT IN THE VALLEYS OF NORTHWEST
MONTANA.

THE LARGE SCALE PATTERN WILL SEE A HIGHLY AMPLIFIED RIDGE OF HIGH
PRESSURE MOVING OVER THE NORTHERN REGION THIS WEEKEND. VERY
STABLE CONDITIONS ANTICIPATED. SOME PATCHY FOG LIKELY DEVELOP IN
THE VALLEYS. MOSTLY CLEAR SKIES CAN BE EXPECTED ABOVE THE LOW
CLOUDS AND ANY FOG THAT DEVELOPS.

SUNDAY NIGHT THROUGH FRIDAY... AN UPPER LEVEL BLOCKING PATTERN
WILL LEAVE THE NORTHERN ROCKIES UNDER A STABLE AIR MASS WITH
VALLEY INVERSIONS INTO THE BEGINNING OF THE WEEK. MODEL GUIDANCE
SUGGESTS THAT THE BLOCKING HIGH SITUATED OVER ALBERTA WILL BE
BROKEN DOWN BY A DEVELOPING PROGRESSIVE NORTHWESTERLY FLOW PATTERN
STARTING TUESDAY. THIS FLOW WILL INITIATE CHANCES FOR PRECIPITATION
FROM TUESDAY ONWARD. COOLING ALOFT ALONG WITH STRONGER SURFACE
PRESSURE GRADIENTS WILL ALSO ACT TO WEAKEN VALLEY INVERSIONS
THROUGH THE MIDDLE AND END OF THE WEEK.

&&

.AVIATION...STRATUS (LOW CLOUDS) WILL CONTINUE TO OCCUPY MOST
VALLEYS ACROSS NORTHWEST MONTANA AND AS FAR SOUTH AS THE MISSOULA
VALLEY...IMPACTING KGPI AND KMSO AIRFIELDS. THESE CLOUDS ARE
EXPECTED TO PERSIST INTO SATURDAY...OBSCURING HIGHER TERRAIN AND
MOUNTAIN PASSES. CLOUD BASES RANGE BETWEEN 2200 & 3200 FT AGL WITH
TOPS APPROXIMATELY 6500 FEET MSL. MORE FAVORABLE FLYING CONDITIONS
CAN BE EXPECTED ACROSS WEST-CENTRAL MONTANA AND NORTH-CENTRAL
IDAHO WHERE MOSTLY CLEAR SKIES WILL PREVAIL.

&&

.AIR STAGNATION...THE LARGE SCALE PATTERN WILL SEE A HIGHLY
AMPLIFIED RIDGE OF HIGH PRESSURE SLOWLY MOVE OVER THE NORTHERN
REGION THIS WEEKEND. VERY STABLE CONDITIONS ANTICIPATED AS WARMER
AIR MOVES OVER THE TOP OF COLDER STAGNATE VALLEY AIR.

&&

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

$$

SHORT TERM...MSJ
LONG TERM....KOLATA
AVIATION...MSJ