776
FXUS65 KTFX 251138
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
438 AM MST SAT JAN 25 2025
AVIATION SECTION UPDATED.
KEY MESSAGES
- LINGERING LIGHT SNOW IN THE MOUNTAINS OF CENTRAL AND SOUTHWEST
MONTANA TO DIMINISH THIS MORNING.
- CLEARING SKIES TONIGHT WILL BRING VERY COLD TEMPERATURES TO THE
VALLEYS OF SOUTHWEST MONTANA.
- A HIGH PRESSURE RIDGE WILL BRING WARMING AND DRYING CONDITIONS
FOR MUCH OF NEXT WEEK, ALONG WITH PERIODS OF GUSTY WINDS OVER
THE PLAINS.
- THE NEXT WIDESPREAD CHANCE FOR PRECIPITATION WITH COOLER
TEMPERATURES MOVES INTO THE AREA FOR NEXT WEEKEND.
DISCUSSION
/ISSUED 318 AM MST SAT JAN 25 2025/
- METEOROLOGICAL OVERVIEW:
LIGHT SNOW IN THE MOUNTAIN AREAS OF CENTRAL AND SOUTHWEST MONTANA
WILL CONTINUE TO DIMINISH THROUGH THIS MORNING, AS WILL BLOWING
SNOW ASSOCIATED WITH GUSTY NORTHWEST WINDS ACROSS JUDITH BASIN AND
FERGUS COUNTIES. OTHERWISE, THE LOW PRESSURE TROUGH RESPONSIBLE
FOR THE SNOW WILL CUT OFF A LOW PRESSURE CENTER THAT WILL MOVE
INTO THE SOUTHWESTERN UNITED STATES, ALLOWING A HIGH PRESSURE
RIDGE OFF THE PACIFIC COAST TO BUILD INTO THE AREA FROM THE
NORTHWEST. THIS WILL SET UP A STAGNANT BLOCKING PATTERN WHERE THE
HIGH PRESSURE RIDGE KEEPS THE FORECAST AREA DRY THROUGH MOST OF
NEXT WEEK WITH A GRADUAL DRYING TREND AND PERIODS OF GUSTY
WESTERLY WINDS OVER THE PLAINS. FORECAST MODELS INDICATE THAT
THIS BLOCKING PATTERN WILL START TO BREAK DOWN LATER NEXT WEEK
INTO THE WEEKEND, BRINGING COOLER TEMPERATURES AND A MORE
WIDESPREAD CHANCE FOR PRECIPITATION.
HOWEVER, LOOKING AT TONIGHT, THE CLEARING SKIES WILL ALLOW
EFFICIENT COOLING OF WIND-PROTECTED VALLEYS OF SOUTHWEST MONTANA,
LIKELY CAUSING LOWS TO FALL INTO THE TEENS AND EVEN 20S BELOW
ZERO. ANY BIT OF WIND THAT DOES BLOW COULD THEN LOWER WIND CHILL
TEMPERATURES INTO THE 20S BELOW ZERO TO AROUND 30 BELOW ZERO.
- FORECAST CONFIDENCE & SCENARIOS:
SOUTHWEST MONTANA COLD TONIGHT:
FORECAST MODEL ENSEMBLES GENERALLY INDICATE THAT THERE IS A 20 TO
40 PERCENT PROBABILITY OF COLD WEATHER ADVISORY CRITERIA
TEMPERATURES (WIND CHILLS OF -25 TO -30 DEGREES F) IN THE
SOUTHWEST MONTANA VALLEYS. HOWEVER, THESE ENSEMBLES HAVE TENDED TO
UNDER-FORECAST HOW MUCH COOLING HAS BEEN OCCURRING IN THESE
VALLEYS WITH CLEARING SKIES AND FRESH SNOW COVER. THEREFORE, HAVE
LEANED MORE TOWARDS THE COLDER DETERMINISTIC MODELS TO BETTER
REFLECT THE CONDITIONS. THIS RESULTED IN AT LEAST MODERATE
CONFIDENCE THAT ADVISORY CRITERIA COULD BE REACHED, WITH A LOW BUT
NOT INSIGNIFICANT CONFIDENCE THAT EVEN COLDER TEMPERATURES COULD
BE REACHED. HAVE THEREFORE EXPANDED THE EXISTING COLD WEATHER
ADVISORY FOR LATER TONIGHT INTO SUNDAY MORNING TO INCLUDE MOST OF
SOUTHWEST MONTANA.
WARMING AND DRYING NEXT WEEK:
ENSEMBLE FORECAST CLUSTERS REMAIN IN GOOD AGREEMENT IN KEEPING
HIGH PRESSURE RIDGING OVER MONTANA THROUGH MUCH OF NEXT WEEK,
PROVIDING HIGH CONFIDENCE THAT DRYING AND MOSTLY WARMING
CONDITIONS WILL OCCUR. HOWEVER, SUBSIDENCE FROM SUCH HIGH PRESSURE
RIDGES USUALLY CAUSE VALLEY INVERSIONS TO OCCUR, WHICH WOULD TEND
TO HINDER WARMING OF TEMPERATURES THERE. THIS PATTERN WILL LIKELY
ALSO BRING GUSTY WESTERLY WINDS TO THE PLAINS THROUGH MUCH OF THE
WEEK, BUT THE ONLY AREA WITH A GREATER THAN 10 PERCENT
PROBABILITY OF GREATER THAN 55 MPH WINDS IS ALONG THE ROCKY
MOUNTAIN FRONT, WHICH IS BELOW HIGH WIND CRITERIA FOR THAT AREA.
POSSIBLE PATTERN CHANGE STARTING NEXT WEEKEND:
THE LATEST RUN OF THE ENSEMBLE CLUSTERS HAVE SLIGHTLY DELAYED THE
BREAK-DOWN OF THE HIGH PRESSURE RIDGE. THE PREVIOUS RUN HAD A
MAJORITY OF THE CLUSTERS STARTING TO BREAK IT DOWN ON FRIDAY, BUT
THIS LATEST RUN DELAYS IT UNTIL SATURDAY. HOWEVER, THE TREND
BEYOND SATURDAY STILL INDICATES THE POTENTIAL FOR A LARGE LOW
PRESSURE TROUGH TO MOVE INTO THE AREA, POSSIBLY INITIATING A
PROLONGED PERIOD OF MUCH COLDER TEMPERATURES. -COULSTON
AVIATION
25/12Z TAF PERIOD
ANY REMAINING LIGHT SNOW WILL DIMINISH THIS MORNING. SOME PATCHY
FOG IS POSSIBLE IN AREAS THAT CLEAR OUT UNTIL MID MORNING.
OTHERWISE GENERALLY VFR CONDITIONS ARE EXPECTED THIS AFTERNOON.
BRUSDA
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION
WEATHER AND HAZARD INFORMATION.
PRELIMINARY POINT TEMPS/POPS
GTF 24 8 29 17 / 0 0 0 0
CTB 25 10 33 20 / 0 0 0 0
HLN 22 -4 23 9 / 10 0 0 0
BZN 18 -14 20 3 / 10 0 0 0
WYS 17 -32 23 -13 / 0 0 0 0
DLN 16 -13 20 5 / 10 0 0 0
HVR 24 11 29 16 / 0 0 0 0
LWT 21 4 32 18 / 0 0 0 0
TFX WATCHES/WARNINGS/ADVISORIES
COLD WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 11 AM MST SUNDAY
FOR BEAVERHEAD AND WESTERN MADISON BELOW 6000FT-ELKHORN AND
BOULDER MOUNTAINS-GALLATIN VALLEY-GALLATIN AND MADISON COUNTY
MOUNTAINS AND CENTENNIAL MOUNTAINS-MADISON RIVER VALLEY-MISSOURI
HEADWATERS-NORTHWEST BEAVERHEAD COUNTY-RUBY MOUNTAINS AND
SOUTHERN BEAVERHEAD MOUNTAINS-UPPER BLACKFOOT AND MACDONALD PASS.
HTTP://WWW.WEATHER.GOV/GREATFALLS
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