FXUS65 KTFX 100419
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
919 PM MST WED DEC 9 2009
.UPDATE...
CURRENT FORECAST IS ON TRACK...WITH JUST A FEW MINOR TWEAKS.
RAISED TEMPERATURES A TOUCH IN THE HAVRE AND LEWISTOWN AREAS.
ADDITIONALLY...A SMALL AREA OF LIGHT SNOW SHOWERS CONTINUES TO
AFFECT THE HAVRE AREA...WHERE UP TO ONE HALF INCH OF SNOWFALL IS
POSSIBLE TONIGHT IN THIS REGION. OTHERWISE...GUSTY DOWNSLOPE
WINDS CONTINUE TO DEVELOP OVER THE REGION...PREVENTING
TEMPERATURES FROM FALLING TO MUCH. THE GUSTY WINDS ARE CREATING
SOME LOW WIND CHILLS THOUGH...THUS THE WIND CHILL ADVISORY WILL
CONTINUE. ADDITIONALLY...AREAS OF BLOWING SNOW CAN BE EXPECTED
ALONG THE FRONT RANGE OF THE ROCKIES AND ADJACENT PLAINS THROUGH
THE NIGHT. A WEAK UPPER LEVEL DISTURBANCE WILL MOVE THROUGH THE
REGION ON THURSDAY...PRODUCING A FEW LIGHT SNOW SHOWERS OR
FLURRIES. BLOWING SNOW WILL CONTINUE IN OPEN AREAS AS WELL.
BRUSDA
&&
.AVIATION...
UPDATED 2355Z.
ALTHOUGH EXPECT VFR CONDITIONS AT THE TAF SITES THERE WILL BE
SCATTERED SNOW SHOWERS OVER THE MOUNTAINS WITH THE POSSIBILITY OF
OBSCUREMENT AT TIMES. CAN NOT RULE OUT ISOLATED SNOW SHOWERS OVER
THE PLAINS EARLY THIS EVENING AND AGAIN ON THURSDAY. DO EXPECT
CEILINGS AT THE TAF SITES THROUGH THE PERIOD BUT HEIGHTS COULD RANGE
ANYWHERE FROM 4000 FT TO WELL ABOVE 15000 FEET. HAVE FAIR CONFIDENCE
IN WINDS FORECAST AT THE TAF SITES. BLANK
&&
.PREV DISCUSSION...
/ISSUED 455 PM MST WED DEC 9 2009/
TONIGHT THROUGH FRIDAY...A BROAD UPPER LEVEL LOW PRESSURE TROF IS
SLOWLY MOVING EAST ALLOWING HIGH PRESSURE TO BUILD ALONG WITH SOME
SLOW WARMING OF THE AIRMASS. A GOOD SURFACE PRESSURE GRADIENT IS
ACROSS THE LEE OF THE ROCKIES AND WINDS WILL REMAIN BRISK ACROSS
THE REGION. THE COMBINATION OF WINDS AND OVER NIGHT TEMPS WILL
DROP MOST WIND CHILLS ACROSS NORTH CENTRAL MONTANA BELOW -20 AND
WILL ISSUE AN ADVISORY FOR TONIGHT. MID-LEVEL WINDS WILL ALSO
REMAIN STRONG AND GRADUALLY SHIFT TO THE WEST BY FRIDAY. THIS WILL
HELP KEEP BRISK SURFACE WINDS IN THE FORECAST THROUGH FRIDAY AS
WELL. WEAK LIFT ASSOCIATED WITH THE AN UPPER LEVEL DISTURBANCE
THAT HAS MOVED INTO THE SOUTHERN ZONES WILL KEEP LIGHT SNOW IN THE
FORECAST...MAINLY ACROSS SOUTHERN GALLATIN AND MADISON COUNTIES.
ANOTHER DISTURBANCE WILL DEVELOP WEAK LIFT TONIGHT AND THURSDAY
BUT THE BEST CHANCE OF SNOW WILL REMAIN OVER THE ROCKIES. ANOTHER
DISTURBANCE WILL PASS ACROSS THE REGION FRIDAY. MOST EFFECT WILL
WILL BE OVER THE ROCKIES AND ACROSS THE NORTH CENTRAL ZONES. WEST
FLOW WILL REMAIN STRONG HOWEVER AND THE AREAS DIRECTLY EAST OF THE
ROCKIES WILL HAVE ONLY A SLIGHT CHANCE FOR SNOW. TEMPS WILL REMAIN
WELL BELOW NORMALS THROUGH THE PERIOD ALTHOUGH THE AIRMASS WILL
TREND STEADILY WARMER THROUGH FRIDAY. ZELZER
FRIDAY NIGHT THROUGH WEDNESDAY...MODELS SHOWING SOME CONSISTENCY
DURING THE MID RANGE. AN UPPER LOW OVER SOUTHERN CANADA CONTINUES TO
STEER THE FLOW ALOFT IN A WEST TO NORTHWEST DIRECTION. MOISTURE AND
PRECIPITATION WITH THIS SETUP WILL BE LIGHT AND MAINLY CONFINED TO
THE MOUNTAINS. THE MODELS THEN BEGIN TO HAVE SOME DISAGREEMENT LATE
SATURDAY. THE GFS IS CURRENTLY THE COLDER AND WETTER WITH MOISTURE
MOVING UP FROM THE SOUTHWESTERN STATES MERGING WITH THE MOISTURE IN
SOUTHERN CANADA AND BRINGING A CHANCE OF SNOW TO MOST OF THE COUNTY
WARNING AREA THROUGH TUESDAY. THE ECMWF DOES NOT TAKE THIS APPROACH
AS IT REMAINS DRIER AND MUCH WARMER THOUGH THE PERIOD. IT KEEPS THE
MAJORITY OF THE CANADIAN MOISTURE ALONG THE WESTERN SIDE OF THE
CONTINENTAL DIVIDE WITH ANY SOUTHERN MOISTURE REMAINING SOUTH OF THE
COUNTY WARNING AREA. WITH THIS SUBSTANTIAL DIFFERING IN OPINIONS IT
GOES WITHOUT SAYING THAT CONFIDENCE IN EXACTLY HOW MUCH
PRECIPITATION AND WHERE IT WILL FALL REMAINS MARGINAL. THE ONE
CONSTANT REMAINS THE SOUTHERLY MOVEMENT OF COLD AIR FROM CANADA SO
HAVE KEPT MONDAY AFTERNOON HIGH TEMPERATURES COLD ACROSS MOST OF
NORTHERN AND CENTRAL MONTANA. MODELS AGAIN DIVERGE IN THEIR
SOLUTIONS BY THE MIDDLE OF NEXT WEEK WITH THE ECMWF MOVING THE
COLD AIR OUT AND BUILDING A WEAK RIDGE WHILE THE GFS KEEPS THE
COLDER AIR IN A BIT LONGER BUT THEN BUILDS A STRONGER RIDGE. AS A
RESULT OF CONFIDENCE BEING WHERE IT IS...HAVE GONE WITH A SLOW
MODERATING TREND WITH TEMPERATURES AND A CONTINUED CHANCE OF SNOW
ACROSS SOUTHWEST AND CENTRAL MONTANA. TEMPERATURES WILL REMAIN BELOW
SEASONAL AVERAGES AND BELOW FREEZING IN MOST LOCATIONS AS WELL.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 2 15 8 28 / 0 20 10 10
CTB 1 13 3 22 / 0 20 10 20
HLN -2 15 5 24 / 10 20 20 10
BZN -15 13 -4 20 / 10 20 20 10
WEY -20 9 -12 12 / 50 30 20 20
DLN -11 14 -3 20 / 10 20 10 10
HVR 4 11 -2 24 / 20 20 10 30
LWT 1 10 0 24 / 10 20 20 10
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY UNTIL 9 AM MST THURSDAY FOR MTZ009>014-
044>051-054.
&&
$$
WEATHER.GOV/GREATFALLS
