004
FXUS65 KMSO 081006
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
306 AM MST THU DEC 8 2022
DISCUSSION
HIGH PRESSURE IS ESTABLISHED OVER THE NORTHERN
ROCKIES THIS MORNING AS THE REGION LIES BETWEEN WEATHER SYSTEMS.
WARM AFTERNOONS THE LAST FEW DAYS HAVE CAUSED SOME SNOW MELT AND
MOISTENED UP THE BOUNDARY LAYER, SO WITH THAT MOISTURE AND THE
STABLE CONDITIONS UNDER THE RIDGE VALLEY FOG HAS BECOME A CONCERN.
THE FOG WILL BE SHORT LIVED AS THE NEXT WEATHER SYSTEM COMES AND
MIXES THINGS UP TONIGHT.
A FAST MOVING, NARROW TROUGH WILL CROSS THE REGION TONIGHT THROUGH
FRIDAY. THIS SYSTEM WILL BE PRETTY MINOR IN TERMS OF SNOW ONLY
LEAVING 4-6 INCHES IN THE CLEARWATER MOUNTAINS AND THE CABINET
MOUNTAINS WITH GENERALLY LESS THAN AN INCH OF SNOW IN THE VALLEYS.
RIGHT AFTER THE TROUGH MOVES THROUGH THE REGION MODELS CONTINUE TO
AGREE VERY WELL ON A CLOSED LOW DIVING SOUTH ALONG THE U.S. WEST
COAST AND MOVING EASTWARD THROUGH THE SOUTHWEST EARLY NEXT WEEK.
THERE IS QUITE A BIT MORE UNCERTAINTY WITH THIS SYSTEM, WHICH IS
TYPICAL OF CLOSED LOWS. MUCH OF THE STATISTICAL GUIDANCE (NBM) HAS
BEEN GOING VERY LOW ON SNOW AMOUNTS BUT IS TRENDING UPWARD,
WHEREAS SOME OF THE PHYSICAL MODELS (ECMWF, GFS) ARE SHOWING A
BROAD CLOSED LOW TRACKING ACROSS SOUTHERN IDAHO AT 700 MB (ABOUT
10,000 FEET). IF THOSE MODELS VERIFY WELL, WE WOULD EXPECT TO SEE
MORE SNOW IN LEMHI COUNTY IDAHO AND BUTTE, MONTANA. CURRENT
FORECASTS HAVE LESS THAN A 10 PERCENT CHANCE OF 5 INCHES OR MORE
OF SNOW IN BUTTE, ANACONDA, AND SALMON FORE EARLY NEXT WEEK.
ONCE THAT LARGE LOW PRESSURE SYSTEM MOVES BY SOME MODELS TRY TO
BUILD IN ANOTHER WEAK RIDGE SIMILAR TO THE ONE WE HAVE NOW, WHILE
OTHERS LEAVE AN ODD, SMALL SCALE LOW PRESSURE SYSTEM OVER THE
COLUMBIA BASIN TO OUR WEST. NEITHER SET UP IS VERY GOOD FOR
BRINGING MORE SNOW TO THE REGION.
AVIATION
HIGH PRESSURE IS ESTABLISHED OVER THE NORTHERN ROCKIES
THIS MORNING AS THE REGION LIES BETWEEN WEATHER SYSTEMS. WARM
AFTERNOONS THE LAST FEW DAYS HAVE CAUSED SOME SNOW MELT AND
MOISTENED UP THE BOUNDARY LAYER. THE MOIST BOUNDARY LAYER AND
STABLE CONDITIONS UNDER THE RIDGE ARE CAUSING AN INCREASED RISK OF
VALLEY FOG. TERMINAL KGPI HAS ALREADY REPORTED SOME FOG LAST
NIGHT, HOWEVER, TERMINAL KMSO HAS KEPT A STEADY DRAINAGE WIND
ALONG THE CLARK FORK RIVER MOST OF THE NIGHT, SO LITTLE IF ANY FOG
IS EXPECTED THERE THIS MORNING. TONIGHT AND FRIDAY A FAST MOVING
TROUGH WILL PREVENT FURTHER FOG BUT WILL ADD SOME LIGHT SNOW
SHOWERS. OVERALL IMPACTS FROM THAT SYSTEM WILL BE MINOR.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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