071
FXUS65 KMSO 280126 AAA
AFDMSO
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MISSOULA MT
626 PM MST FRI NOV 27 2009
UPDATE...INCREASED POPS IN CAMAS PRAIRIE
LOWER HELLS CANYON AND
BUTTE AREAS FOR THIS EVENING. ADJUSTED AND ADDED FOG COVERAGE
ACROSS AREA VALLEYS FOR TONIGHT AND SATURDAY MORNING.
DISCUSSION
A LOW PRESSURE SYSTEM IN THE GREAT BASIN WILL
CONTINUE TO DIVE SOUTHWARD THIS EVENING AND OVERNIGHT...TAKING THE
BULK OF ENERGY WITH IT. HOWEVER THERE IS ENOUGH LINGERING MOISTURE
AND LOW LEVEL INSTABILITY TO KEEP RAIN AND HIGH ELEVATION SNOW IN
A LINE FROM MULLAN PASS TO SEELEY LAKE AND POINTS SOUTH THROUGH
THIS EVENING.
FOG WILL ONCE AGAIN BE A CONCERN TONIGHT GIVEN THE AMOUNT OF
AVAILABLE LOW LEVEL MOISTURE ACROSS THE REGION FROM RECENT
PRECIPITATION AND EXPECTED CLEARING FROM NORTHWEST TO SOUTHEAST
THROUGH THE NIGHT. DENSE FOG COULD BE POSSIBLE AT TIMES TONIGHT
THROUGH SATURDAY MORNING.
AVIATION
PRECIPITATION IN THE FORM OF VALLEY RAIN AND HIGH
ELEVATION SNOW SHOULD LINGER THROUGH THIS EVENING AND THEN TAPER
OFF IN VALLEY LOCATIONS AFTER MIDNIGHT IN NORTH CENTRAL IDAHO AND
PORTIONS OF WEST CENTRAL AND SOUTHWEST MONTANA. KBTM WILL BE
IMPACTED BY LIGHT SNOW THIS EVENING AND POTENTIALLY REDUCED
VISIBILITIES THIS EVENING THROUGH SATURDAY MORNING. ELSEWHERE...
FOG DEVELOPMENT IS EXPECTED ONCE AGAIN THIS EVENING ACROSS THE
NORTHERN ROCKIES AS THE COMBINATION OF CLEARING SKIES AND ABUNDANT
LOW LEVEL MOISTURE FROM RECENT PRECIPITATION WILL KEEP THE LOWER
ATMOSPHERE SATURATED. FOG IS EXPECTED TO LINGER THROUGH SATURDAY
MORNING BEFORE DISSIPATING.
PREV DISCUSSION
/ISSUED 254 PM MST FRI NOV 27 2009/
DISCUSSION...
TONIGHT THROUGH SATURDAY NIGHT...A WEAKENING PACIFIC STORM
SYSTEM...CURRENTLY SPLITTING INTO TWO SEPARATE SYSTEMS NORTH AND
SOUTH...WILL CONTINUE TO BRING MOIST CONDITIONS TO NORTH CENTRAL
IDAHO AND WESTERN MONTANA DURING THE EVENING AND OVERNIGHT TONIGHT.
THE LOWER LEVELS OF THE ATMOSPHERE HAVE BECOME SATURATED AT MANY
LOCATIONS...MOST NOTEWORTHY WITH FOG DEVELOPMENT ACROSS THE CAMAS
PRAIRIE IN IDAHO. AS THE UPPER LEVEL CLOUD SHIELD CONTINUES TO
MOVE EAST OVERNIGHT...HIGH CLOUDINESS WILL DIMINISH SIGNIFICANTLY
OVER IDAHO BY MIDNIGHT. GIVEN THE SLIGHTLY COOLER AIR ALOFT TO BE
PRESENT THROUGH THIS EVENING...MOST OF THE FOG IN IDAHO IS
ANTICIPATED TO LIFT TO A LOW STRATUS DECK OVERNIGHT.
HOWEVER...AREAS OF FOG ARE EXPECTED TO DEVELOP IN NORTHWEST
MONTANA DURING THIS SAME TIME WITH LOW STRATUS ALREADY IN PLACE.
GIVEN HOW WEAK THIS SYSTEM IS AND HOW LITTLE COOLING HAS BEEN
ASSOCIATED WITH ITS PRESENCE...TEMPERATURES ARE NOT EXPECTED TO
COOL SIGNIFICANTLY ACROSS THE AREA. BY MIDDAY
SATURDAY...NORTHWESTERLY FLOW WILL BECOME THE DOMINANT FEATURE
PRESENT OVER NORTHWEST MONTANA. MODELS DEPICT A RELATIVELY STRONG
PORTION OF THE PACIFIC JET STREAM OVER NORTHWEST MONTANA DURING
SATURDAY...LIKELY TO FORCE A MAINLY TERRAIN LOCKED SNOW EVENT. NO
SIGNIFICANT SNOW ACCUMULATIONS ARE EXPECTED SATURDAY.
SUNDAY THROUGH FRIDAY...THE ECMWF REMAINS THE PREFERRED MODEL FOR THE
EXTENDED FORECAST PERIOD WITH ITS GENERAL LEVEL OF CONSISTENCY.
A LOW PRESSURE TROUGH WILL DROP OUT OF CANADA AND THROUGH THE
NORTHERN ROCKIES ON TUESDAY. THIS TROUGH DOES NOT LOOK AS COLD OR
MOIST AS GUIDANCE PREVIOUSLY PROJECTED...BUT LIGHT SNOW AND COOLER
CONDITIONS ARE POSSIBLE ON TUESDAY FROM NEAR THE MONTANA/IDAHO
BORDER AND EASTWARD. A BROAD TROUGH OF LOW PRESSURE WILL DOMINATE THE
MAJORITY OF THE UNITED STATES AFTER TUESDAY WITH NORTH CENTRAL IDAHO
AND WESTERN MONTANA UNDER A COOL AND POTENTIALLY ACTIVE NORTHWESTERLY
FLOW PATTERN.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
UPDATE...DEROSA
PREVIOUS DISCUSSION...ZUMPFE/KITSMILLER
AVIATION...DEROSA
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