FXUS65 KMSO 251525 AAA
AFDMSO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MISSOULA MT
825 AM MST FRI DEC 25 2009

.UPDATE...INCREASED SKY COVER ACROSS NORTHWEST MONTANA.

&&

.DISCUSSION...NORTHERLY FLOW REMAINS PERSISTENT OVER THE NORTHERN
ROCKIES THIS MORNING AS AN UPPER LEVEL RIDGE AMPLIFIES ALONG THE
PACIFIC COAST. A STRATUS DECK OVER NORTHWEST MONTANA IS EXPECTED
TO CONTINUE THROUGH THE DAY AS A JET STREAK MOVING OVER THE AREA
SHOULD AID IN ADDITIONAL LIFT FOR CLOUD FORMATION TO PERSIST.

&&

.AVIATION...A NORTHERLY FLOW ALOFT WITH A JET STREAK OVER THE
REGION WILL ALLOW A STRATUS DECK IN NORTHWEST MONTANA TO PERSIST
THROUGH THE DAY. MID LEVEL CLOUDS CAUGHT UP IN THE NORTHERLY FLOW
WILL ALSO TRACK OVER THE NORTHERN ROCKIES TODAY. OVERALL THE
CLOUD COVER ACROSS THE REGION WILL HAVE LITTLE EFFECT ON AVIATION
OTHER THAN THE HIGHER TERRAIN BEING OBSCURED AT TIMES THROUGH THE
DAY. 

&&

.PREV DISCUSSION... /ISSUED 327 AM MST FRI DEC 25 2009/ 

DISCUSSION...A NORTHERLY FLOW WILL REMAIN OVER THE NORTHERN
ROCKIES TODAY...WITH LITTLE CONSEQUENCE OTHER THAN TO BRING A FEW
MID TO HIGH LEVEL CLOUDS OVER THE AREA. AN UPPER LEVEL RIDGE WILL
BEGIN TO FURTHER INFLUENCE WESTERN MONTANA AND NORTH CENTRAL IDAHO
TONIGHT INTO THE WEEKEND AS IT SHIFTS EASTWARD. THIS WILL ALLOW
FOR STRENGTHENING INVERSIONS...VALLEY FOG...AND BETTER RADIATIONAL
COOLING AT NIGHT THROUGH THE WEEKEND.

MONDAY 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.

AIR STAGNATION...STABLE CONDITIONS EXIST OVER THE NORTHERN
ROCKIES UNDER A NORTHERLY FLOW ALOFT. A HIGHLY AMPLIFIED RIDGE OF
HIGH PRESSURE WILL MOVE OVER THE INTER-MOUNTAIN WEST FURTHER
STABILIZING THE LOWER ATMOSPHERE THROUGH THE WEEKEND. THIS PATTERN
FAVORS STRENGTHENING VALLEY INVERSIONS AND POOR MIXING.

&&

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

$$

UPDATE...DEROSA
PREVIOUS DISCUSSION...PALLISTER/KITSMILLER
AVIATION...DEROSA