FXUS65 KTFX 301145
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
445 AM MST MON NOV 30 2009
UPDATED AVIATION DISCUSSION
.DISCUSSION...
TODAY THROUGH WEDNESDAY...THE PERIOD WILL BEGIN WITH AN UPPER
LEVEL RIDGE OVER THE WESTERN US. A SHORTWAVE WILL MOVE OVER THE
WEST COAST THIS EVENING AND OVER THE ROCKIES BY MIDNIGHT
TUESDAY...AND STRONG NORTH FLOW WILL FOLLOW DURING THE DAY. AHEAD
OF THIS FRONT...A DISTURBANCE WILL CROSS THE ROCKIES AND ZONES MID
DAY TODAY. THIS WILL FLATTEN THE RIDGE AND KICK UP STRONG WINDS
ALONG THE NORTHERN ROCKIES AND NORTH CENTRAL MONTANA. A TIGHT
SURFACE PRESSURE GRADIENT IS ALREADY IN PLACE ACROSS THE LEE
SLOPES OF THE ROCKIES. A TEMPERATURE INVERSION NEAR MOUNTAIN TOP
LEVEL WILL BE IN PLACE THIS MORNING BUT STABILITY WEAKENS AS THE
DAY PROGRESSES...AND MAY HOLD BACK SOME OF THE STRONGEST WINDS AS
THE JET CORE MOVES THROUGH. WILL START THE WARNING AT 12Z TODAY
OVER THE NORTHERN ROCKIES AND EASTERN GLACIER COUNTY SINCE SOME
GOOD GUSTS ARE DEVELOPING AHEAD OF THE SHORTWAVE. A FAIRLY SHARP
TROF WILL MOVE OVER NORTHWEST MONTANA BY MIDNIGHT TUESDAY. GOOD
DYNAMICS WILL BRING AN ASSOCIATED COLD FRONT QUICKLY THROUGH THE
AREA...STRONGEST LIFT WILL BE ASSOCIATED WITH THE FRONT BUT NOT
REALLY LONG LASTING. HOWEVER...UP SLOPE FLOW WILL THROUGH TUESDAY
FOR CONTINUED LIGHT SNOW. THE MAIN SLUG OF MOISTURE SHOULD CROSS
THE BORDER AFTER 06Z TUE AND ACROSS KCTB AND KHVR BY 09Z. MOISTURE
JUMPS QUICKLY INTO THE CENTRAL ZONES DURING THE MORNING. SNOW WILL
WEAKEN BY TUESDAY AFTERNOON...NORTHEAST ZONES...KHVR...SHOULD STAY
MOIST INTO THE EVENING BUT THEN QUICKLY DRY. THE AIRMASS WILL COOL
QUICKLY BEHIND THE FRONT. COLD AIR CONTINUES TO MOVE INTO THE AREA
THROUGH TUESDAY NIGHT...COLDEST 500MB TEMPS OVER OUR EASTERN ZONES
AND EASTERN MONTANA WILL BE IN THE -35C RANGE. THE AIRMASS DRIES
QUICKLY ON WEDNESDAY BUT TEMPS RECOVERY WILL BE DIFFICULT AFTER
COLD OVERNIGHT LOWS. ZELZER
WEDNESDAY NIGHT THROUGH SATURDAY NIGHT...EXPECT A SEASONABLY COLD
AND DRY PERIOD OF WEATHER TO BEGIN THE PERIOD...AS A NORTHERLY FLOW
ALOFT RESIDES OVER THE REGION. TEMPERATURES WILL RANGE FROM 4 TO 8
DEGREES BELOW NORMAL THURSDAY...THEN MODERATE A FEW DEGREES FOR
FRIDAY...BEFORE COOLING OFF AGAIN ON SATURDAY. OVERALL...I WENT WITH
THE ECMWF MODEL...WHICH IS DRIER AND WARMER THROUGH SATURDAY. THE
GFS MODEL CONTINUES TO PROG MUCH COLDER AIR...AND PERIODS OF
SNOW...TO MOVE INTO THE REGION AS EARLY AS FRIDAY...BUT SINCE THE
GFS HAS SHOWN A TREND TO GO SLOWER WITH THIS COLD AIR MASS...I WENT
WITH THE ECMWF OVERALL...THUS THE MILDER/DRIER WEATHER PATTERN.
HOWEVER...THIS SITUATION WILL NEED TO BE WATCHED CLOSELY OVER THE
NEXT FEW DAYS...AS TEMPERATURES COULD BE OVER 20 DEGREES COLDER THAN
CURRENTLY FORECASTED SHOULD THE GFS PAN OUT...ALONG WITH A MUCH
BETTER CHANCE FOR SNOW. BRUSDA
SUNDAY THROUGH MONDAY...MODEL DIFFERENCES LESS SIGNIFICANT ON THIS
RUN...WITH BOTH ECMWF AND GFS INDICATING A DRAMATIC CHANGE TO WINTER
LIKE CONDITIONS. NORTHERLY SURFACE WINDS...PLUNGING TEMPERATURES AND
A CHANCE OF SNOW IS INDICATED. DUE TO SOME UNCERTAINTY PRECIPITATION
PROBABILITIES ARE KEPT NEAR CLIMO VALUES. MONDAY...LIGHTER UPSLOPE
WINDS AND DRIER AIR ALOFT SHOULD RESULT IN SNOW TAPERING OFF OVER
THE NORTH. DAYTIME TEMPERATURES WILL FALL INTO THE TEENS TO NEAR 20
WITH LOWS IN SINGLE DIGITS ABOVE OR BELOW ZERO. EK
&&
.AVIATION...
UPDATED 1145Z.
AN UPPER LEVEL TROF WILL APPROACH THE REGION TONIGHT. AHEAD OF THIS
TROF...EXPECT STRONG DOWNSLOPE WINDS AT THE SURFACE OVER THE ROCKY
MOUNTAIN FRONT AND THE ADJACENT PLAINS. FREQUENT GUSTS AROUND 50
KNOTS CAN BE EXPECTED IN THE CUT BANK AREA AND 45 KNOTS IN THE HAVRE
AND GREAT FALLS AREA. OTHERWISE GENERALLY VFR CONDITIONS CAN BE
EXPECTED TODAY. A COLD FRONT WILL MOVE INTO THE CUT BANK AREA AROUND
6Z TUESDAY AND THE GREAT FALLS AND HAVRE AREAS AROUND 10Z. EXPECT
LOWERING CEILINGS ALONG WITH A CHANCE FOR SNOW SHOWERS...AS
CONDITIONS FALL TO NEAR IFR CONDITIONS BY 10Z.
ADDITIONALLY...MOUNTAINS OVER CENTRAL AND NORTH CENTRAL MONTANA WILL
BECOME OBSCURED BY 08Z. OVERALL...VFR CONDITIONS WILL PREVAIL OVER
SOUTHWEST MONTANA UNTIL 12Z TUESDAY. BRUSDA
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 55 25 28 6 / 0 50 70 10
CTB 51 23 27 5 / 0 50 70 10
HLN 51 29 33 17 / 0 30 60 10
BZN 46 26 30 -3 / 0 20 60 10
WEY 34 16 26 0 / 0 10 40 20
DLN 45 22 30 8 / 0 10 40 10
HVR 55 25 32 4 / 0 40 60 10
LWT 56 22 25 5 / 0 40 50 10
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM NOON TODAY TO MIDNIGHT MST TONIGHT FOR
MTZ044-046-049.
HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT FOR MTZ009-010-048.
&&
$$
WEATHER.GOV/GREATFALLS
