FXUS65 KTFX 040553
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1050 PM MST THU DEC 3 2009
...UPDATE TO AVIATION...
.DISCUSSION...
UPDATE FORTHCOMING. HAVE MADE ADJUSTMENTS TO OVERNIGHT LOW
TEMPERATURES AT SOME LOCATIONS TO BETTER ALIGN WITH CURRENT
CONDITIONS. WEAK RIDGING WILL CONTINUE OVER THE AREA TONIGHT WITH A
GRADUAL INCREASE IN HIGH CLOUDS AFTER MIDNIGHT. MAIN FORECAST EVENT
CONTINUES TO BE THE ANTICIPATED UPPER LOW ARRIVAL OVER THE AREA
BEGINNING FRIDAY NIGHT. WILL CONTINUE THE WINTER STORM WATCH FOR
FRIDAY NIGHT THROUGH SATURDAY AND AWAIT FURTHER ANALYSIS OF 00Z RUNS
BY SUCCEEDING SHIFTS. EMANUEL
&&
.AVIATION...
UPDATED 0550Z.
VFR CONDITIONS WILL CONTINUE ACROSS NORTH CENTRAL...CENTRAL...AND
SOUTHWEST MONTANA THROUGH AT LEAST 21Z FRIDAY...WITH CONDITIONS
DETERIORATING AFTER THAT. AN UPPER LEVEL HIGH PRESSURE RIDGE WILL
KEEP AREAS OF MAINLY HIGH CLOUDS MOVE OVER THE AREA. SOUTHERLY WINDS
WILL INCREASE ACROSS THE PLAINS OF NORTH CENTRAL AND CENTRAL MONTANA
OVERNIGHT INTO FRIDAY. WINDS WILL BECOME QUITE GUSTY ALONG THE ROCKY
MOUNTAIN FRONT AND OUT TO KCTB AND KGTF DURING THIS TIME...AS GUSTS
WILL MOSTLY BE IN THE 30 TO 40 KT RANGE. A CANADIAN COLD FRONT AHEAD
OF A SHORTWAVE TROUGH APPROACHING FROM THE NORTHWEST WILL THEN MOVE
INTO NORTH CENTRAL MONTANA AFTER 20Z FRIDAY...SPREADING LOW MVFR/IFR
CONDITIONS AND MOUNTAIN OBSCURATION IN LIGHT SNOW FROM THE KCTB AND
KHVR TERMINALS AROUND 00Z SATURDAY INTO THE KGTF/KLWT/KHLN AREAS BY
06Z. THE BREEZY WINDS WILL ALSO SHIFT MORE OUT OF THE NORTHWEST
BEHIND THE FRONT. COULSTON
&&
.PREV DISCUSSION...ISSUED 346 PM MST THU DEC 3 2009
TONIGHT THROUGH FRIDAY...AN UPPER-LEVEL RIDGE WILL CONTINUE TO
BUILD OVER THE REGION OVERNIGHT AND THEN MOVE EAST BY FRIDAY.
GENERALLY CLEAR CONDITIONS AND WARMER TEMPERATURES ARE EXPECTED ON
FRIDAY BUT WILL STILL REMAIN SLIGHTLY BELOW AVERAGE. A SHORTWAVE
TROUGH WILL ALSO MOVE OVER THE BC COAST FRIDAY MORNING AND
PROGRESS TOWARDS THE IDAHO PANHANDLE BY 00Z SATURDAY WITH LOW-
LEVEL WINDS INCREASING OVER THE ROCKY MOUNTAIN FRONT AND ADJACENT
PLAINS DURING THE AFTERNOON.
FRIDAY NIGHT THROUGH SATURDAY...A STRONG ARCTIC COLD FRONT AND
UPPER-LEVEL TROUGH WILL APPROACH NORTHERN MONTANA BY FRIDAY
EVENING AND PROGRESS SOUTHWARD INTO CENTRAL MONTANA FRIDAY NIGHT
AND INTO SOUTHWEST MONTANA ON SATURDAY. THIS ARCTIC COLD FRONT
WILL COMBINE WITH PACIFIC MOISTURE TO BRING WIDESPREAD SNOW TO THE
FORECAST AREA WITH SIGNIFICANT ACCUMULATIONS POSSIBLE...HOWEVER
EXACT AMOUNTS ARE STILL UNCERTAIN GIVEN THE UNCERTAINTY IN THE
MODELS TO THE POSITIONING OF THE MAIN UPPER-LEVEL LOW. WHILE SNOW
WILL PROGRESS INTO SOUTHWEST MONTANA ON SATURDAY...EASTERLY
COMPONENT WINDS SHOULD KEEP SNOW ACCUMULATIONS LOWER...PARTICULARLY
IN THE VALLEYS BUT WE WILL CONTINUE TO MONITOR AND UPDATE
ACCORDINGLY. MOISTURE AVAILABILITY IS ALSO A CONCERN
OVERALL...HOWEVER LATEST WATER VAPOR IMAGERY IS INDICATING A FAIR
AMOUNT OF PACIFIC AND GULF OF ALASKA MOISTURE MOVING OVER THE
CANADIAN ROCKIES SO AM EXPECTING THIS MOISTURE TO PERSIST AS THE
ARCTIC FRONT MOVES SOUTH INTO THE FORECAST AREA. IN ADDITION...VERY
COLD AIR WILL SPREAD OVER THE AREA WITH GUSTY WINDS INITIALLY
CAUSING AREAS OF BLOWING SNOW ALONG AND JUST BEHIND THE COLD FRONT
AND WIND CHILLS AS LOW AS 25 BELOW ZERO. THIS COMBINATION OF
SNOW...GUSTY WINDS AND COLD AIR WILL CREATE HAZARDOUS TRAVEL
CONDITIONS AND IMPACT SO DECIDED TO ISSUE A WINTER STORM WATCH FOR
ALL OF NORTH-CENTRAL AND PORTIONS OF CENTRAL MONTANA. CURRENT
STORM TOTAL SNOWFALLS OF 4 TO 8 INCHES OVER THE PLAINS AND 8 TO 12
INCHES IN THE MOUNTAINS ARE EXPECTED...HOWEVER HIGHER AMOUNTS ARE
POSSIBLE AND WILL CONTINUE TO MONITOR VERY CLOSELY AND UPDATE. MLS
SATURDAY NIGHT THROUGH TUESDAY NIGHT...FORECAST MODELS CONTINUE TO
INDICATE THE POTENTIAL FOR A FEW WIDESPREAD VERY COLD NIGHTS OVER
THE REGION...WITH THE COLDEST TEMPERATURES OCCURRING MONDAY AND
TUESDAY MORNINGS. PERIODS OF LIGHT SNOW ARE EXPECTED TO CONTINUE
SATURDAY NIGHT AND INTO SUNDAY MORNING. MUCH COLDER...ARCTIC
AIR...WILL CONTINUE TO MOVE INTO THE REGION ON SUNDAY. FORECAST
MODELS ARE STARTING TO PROG WIDESPREAD MONDAY MORNING LOW
TEMPERATURES RANGING FROM 25 BELOW TO 40 BELOW ZERO. HOWEVER...WE
NEED THE PERFECT CONDITIONS FOR THESE VERY COLD TEMPERATURES TO
OCCUR...(LIGHT WINDS...CLEAR SKIES...AND A FRESH SNOW COVER).
CURRENT FORECAST MODELS STILL INDICATE WE WILL HAVE A CLOUD COVER
WITH A FEW FLURRIES MONDAY MORNING...THUS I DID NOT GO AS COLD AS
POSSIBLE. ON TUESDAY MORNING...I DID FORECAST LOWS IN THE -30
RANGE FOR THE COLDER LOCATIONS...WITH MUCH OF SOUTHWEST MONTANA
COLDER THAN 10 BELOW. OVERALL...THIS SITUATION NEEDS TO BE
MONITORED CLOSELY OVER THE NEXT FEW DAYS...BECAUSE IF THE PERFECT
WEATHER CONDITIONS DO SET UP MONDAY OR TUESDAY MORNING...SEVERAL
PLACES COULD START TO APPROACH RECORD LOWS. FOR WEDNESDAY...EXPECT
A CHANCE FOR SNOW...ESPECIALLY OVER SOUTHWEST MONTANA...AS
TEMPERATURES START TO REBOUND A BIT. BRUSDA
WEDNESDAY AND THURSDAY...MODELS CONTINUE TO SHOW A COLD UPPER LEVEL
LOW OVER CENTRAL CANADA...BRINGING COLD ARCTIC AIR INTO THE REGION
UNDER A NORTHERLY FLOW ALOFT ON WEDNESDAY. THE FLOW BECOMES MORE
NORTHWESTERLY AS A WEAK SURFACE TROUGH DEVELOPS ACROSS CENTRAL
MONTANA. THIS WILL RESULT IN SOME SOUTHWEST WINDS WITH SOME
MODERATION IN TEMPERATURES. IT WILL BE MOSTLY DRY ACROSS THE NORTH
AND EAST WITH ISOLATED TO SCATTERED SNOW SHOWERS OVER THE SOUTHWEST
AND ALONG THE CONTINENTAL DIVIDE. WILLIAMSON DC
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 9 32 14 16 / 0 0 90 80
CTB 8 34 12 14 / 0 10 90 70
HLN 6 29 16 18 / 0 0 90 80
BZN -15 20 6 19 / 0 0 40 70
WEY -26 14 -6 11 / 0 0 40 60
DLN -1 26 6 15 / 0 0 40 70
HVR 2 33 14 20 / 0 0 80 70
LWT -2 32 11 14 / 0 0 80 80
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH LATE SATURDAY
NIGHT FOR MTZ009>014-044>051-054.
&&
$$
SHORT TERM...EMANUEL/MLS
LONG TERM...BRUSDA/WILLIAMSON DC
AVIATION...COULSTON
WEATHER.GOV/GREATFALLS
