776
FXUS65 KTFX 291129
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
429 AM MST WED JAN 29 2025
AVIATION SECTION UPDATED.
KEY MESSAGES
- WINDY OVER THE PLAINS TODAY THROUGH AT LEAST TONIGHT,
ESPECIALLY ON THE ROCKY MOUNTAIN FRONT.
- COLD AIR WILL LINGER IN THE VALLEYS OF CENTRAL AND SOUTHWEST
MONTANA THROUGH AT LEAST THURSDAY, POSSIBLY WITH SOME GRADUAL
WARMING BEGINNING ON FRIDAY.
- A PACIFIC WEATHER SYSTEM WILL BRING SNOW TO THE MOUNTAINS ON
THE CONTINENTAL DIVIDE FRIDAY THROUGH SATURDAY, WHICH WILL
SPREAD OVER MUCH OF THE AREA OVER THE WEEKEND AND INTO EARLY
NEXT WEEK.
- ANOTHER ROUND OF WINDY CONDITIONS ARE POSSIBLE ON SATURDAY
AHEAD OF A STRONG COLD FRONT, WHICH WILL BRING MUCH COLDER
TEMPERATURES STARTING ON SUNDAY.
DISCUSSION
/ISSUED 409 AM MST WED JAN 29 2025/
- METEOROLOGICAL OVERVIEW:
A HIGH PRESSURE RIDGE EXTENDING WEST TO EAST FROM THE PACIFIC
NORTHWEST COAST WILL KEEP THE AREA MOSTLY DRY WITH BREEZY WINDS
OVER THE PLAINS THROUGH AT LEAST FRIDAY. DISTURBANCES MOVING OVER
THIS RIDGING WILL CONTINUE TO INCREASE WESTERLY WINDS ALOFT TODAY
THROUGH TONIGHT, INCREASING DOWNSLOPING WINDS OVER THE PLAINS.
THIS WILL BE ESPECIALLY TRUE ON THE ROCKY MOUNTAIN FRONT AND
ADJACENT PLAINS, WHERE THE PRESSURE GRADIENT WILL BE STRONGEST
ALONG A SURFACE TROUGH TO THE LEE OF THE ROCKIES. AREAS ALONG THE
MT HIGHWAY 200 CORRIDOR FROM WEST OF GREAT FALLS EAST TO EDDIE'S
CORNER AND SOUTH TO JUDITH GAP COULD SEE GUSTS UP TO 50 MPH AT
TIMES, BUT GUSTS OF 60 TO 75 MPH ARE POSSIBLE ON THE ROCKY
MOUNTAIN FRONT AND ADJACENT PLAINS EAST TO THE CUT BANK AREA.
GUSTS ELSEWHERE ON THE PLAINS WILL MOSTLY BE IN THE 30 TO 40 MPH
RANGE. WINDS WILL DECREASE SOMEWHAT THURSDAY INTO FRIDAY BUT
REMAIN BREEZY. THESE WINDS OVER THE PLAINS WILL KEEP TEMPERATURES
THERE AROUND 10 DEGREES ABOVE NORMAL. HOWEVER, THE HIGH PRESSURE
RIDGING WILL MAINTAIN TEMPERATURE INVERSIONS IN THE VALLEYS OF
CENTRAL AND SOUTHWEST MONTANA, KEEPING TEMPERATURES THERE AT LEAST
10 DEGREES BELOW NORMAL, WITH LOWS IN SOME VALLEYS FALLING BELOW
ZERO AGAIN TONIGHT AND THURSDAY NIGHT, SIMILAR TO THE LAST NIGHT
OR TWO.
AN PACIFIC LOW PRESSURE TROUGH WITH AN ASSOCIATED STRONG COLD
FRONT IS FORECAST TO APPROACH THE AREA ON FRIDAY, INITIALLY
BRINGING LIGHT MEASURABLE SNOW TO THE MOUNTAINS ALONG THE
CONTINENTAL DIVIDE FRIDAY THROUGH SATURDAY. HOWEVER, AHEAD OF THE
COLD FRONT MOVING SOUTH OUT OF CANADA, WESTERLY WINDS MAY BECOME
STRONG ONCE AGAIN ON THE ROCKY MOUNTAIN FRONT. MORE SOUTHERLY
WINDS BLOWING THROUGH THE VALLEYS OF SOUTHWEST MONTANA AHEAD OF
THIS FRONT MAY HELP SCOUR OUT SOME OF THE COLD AIR THERE. THE
PASSAGE OF THIS COLD FRONT SATURDAY NIGHT OVER NORTH CENTRAL AND
CENTRAL MONTANA WILL SHIFT WINDS MORE NORTHERLY THERE, USHERING
IN COLD ARCTIC AIR THAT COULD BRING A PERIOD OF HIGHS IN THE
SINGLE DIGITS ABOVE AND BELOW ZERO AND LOWS IN THE SINGLE DIGITS
AND TEENS BELOW ZERO. IRONICALLY, CONSIDERING THE COLD AIR
CURRENTLY TRAPPED IN THE SOUTHWEST VALLEYS, THIS BITTER COLD AIR
IS NOT FORECAST TO MOVE COMPLETELY IN THERE WITH THIS SYSTEM.
REGARDLESS, THE SYSTEM IS TAPPING INTO A GOOD FEED OF PACIFIC
MOISTURE, SO IT SHOULD BRING PERIODS OF LIGHT TO MODERATE SNOW TO
MUCH OF THE FORECAST AREA SATURDAY THROUGH NEXT WEDNESDAY;
HOWEVER, FORECAST MODELS CONTINUE TO KEEP THE MAIN FOCUS FOR SNOW
OVER SOUTHWEST AND CENTRAL MONTANA.
- FORECAST CONFIDENCE & SCENARIOS:
WINDS ON THE ROCKY MOUNTAIN FRONT:
NBM GUIDANCE ONLY GIVES A 40 TO 50 PERCENT PROBABILITY THAT EITHER
SUSTAINED WINDS OR WIND GUSTS WILL HIT HIGH WIND CRITERIA FOR THE
NORTHERN HIGH PLAINS ZONE AND EASTERN GLACIER / WESTERN TOOLE /
CENTRAL PONDERA ZONE. HOWEVER, THESE PROBABILITIES HAVE BEEN
UNDERDONE WITH THE LAST COUPLE OF EVENTS. ALSO, A STRONG SURFACE
PRESSURE GRADIENT, PAIRED WITH A STRONG STABLE LAYER JUST OFF THE
SURFACE AND 40 TO 50 KT WINDS JUST BELOW THAT LAYER, IS A GOOD
RECIPE FOR STRONG WINDS IN THAT AREA. WILL THEREFORE CONTINUE THE
HIGH WIND WARNING FOR THOSE TWO ZONES THROUGH 6 AM MST THURSDAY.
SIMILAR PROBABILITIES DEVELOP AGAIN FRIDAY NIGHT INTO SATURDAY
AHEAD OF THE COLD FRONT, WHICH FAVORS ANOTHER PERIOD OF STRONG
WINDS THEN.
COLD AND SNOW THIS WEEKEND INTO EARLY NEXT WEEK:
THE INITIAL PUSH OF SNOW ON THE CONTINENTAL DIVIDE SATURDAY INTO
SATURDAY NIGHT HAS A 24-HOUR PROBABILITY OF 8+ INCHES OF SNOW OF
50+ PERCENT ABOVE MOUNTAIN PASS LEVEL, BUT MOST MOUNTAIN AREAS
HAVE A LESS THAN 40 PERCENT CHANCE AFTER THEN FOR ANY GIVEN 24
HOUR PERIOD. THE 24-HOUR PROBABILITY OF 4+ INCHES OF SNOW ALSO
NEVER EXCEEDS 30 PERCENT AT LOWER ELEVATIONS FOR ANY GIVEN PERIOD.
THEREFORE, WINTER STORM WATCHES MAY EVENTUALLY BE NEEDED FOR THE
MOUNTAINS, WITH LESSER AMOUNTS AT LOWER ELEVATIONS POSSIBLY
NEEDING WINTER WEATHER ADVISORIES. HOWEVER, CONFIDENCE IN EXACT
SNOW AMOUNTS AT THIS TIME IS ONLY LOW TO MODERATE GIVEN THE RECENT
VARIABILITY IN THE PATH OF THE HEAVIEST SNOW.
TEMPERATURES ARE EXPECTED TO BE MUCH COLDER THAN NORMAL BEHIND THE
COLD FRONT PASSAGE, BUT THERE IS A LOT OF UNCERTAINTY AS TO
WHETHER THE TEMPERATURES WILL BE EXTREMELY COLD. ENSEMBLE FORECAST
MODEL CLUSTERS HAVE THE FORECAST AREA UNDER A SOMEWHAT ANOMALOUSLY
COLD AIRMASS, BUT A SIMILARLY ANOMALOUS HIGH PRESSURE AREA IS
FORECAST OVER THE SOUTHERN AND CENTRAL ROCKIES AT THE SAME TIME.
THIS WILL NEED TO BE WATCHED CLOSELY, AS A SHIFT ONE WAY OR THE
OTHER COULD IMPACT JUST HOW COLD IT WILL GET. -COULSTON
AVIATION
29/06Z TAF PERIOD
VFR CONDITIONS WILL CONTINUE TO PREVAIL OVER THE CWA THROUGH THE
PERIOD. THE EXCEPTION TO THE QUIET WEATHER WILL BE STRONG WINDS
TODAY ALONG THE ROCKY MOUNTAIN FRONT AND IN THE BROWNING/CUT BANK
AREAS. EXPECT THE WIND SPEEDS TO DIMINISH A BIT THIS EVENING.
BRUSDA
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION
WEATHER AND HAZARD INFORMATION.
PRELIMINARY POINT TEMPS/POPS
GTF 48 29 46 30 / 0 0 0 0
CTB 49 27 44 26 / 0 0 0 0
HLN 22 4 27 6 / 0 0 0 0
BZN 23 -4 27 0 / 0 0 0 0
WYS 24 -13 28 -11 / 0 0 0 0
DLN 30 5 32 7 / 0 0 0 0
HVR 44 20 41 20 / 0 0 0 10
LWT 45 19 45 23 / 0 0 0 0
TFX WATCHES/WARNINGS/ADVISORIES
HIGH WIND WARNING UNTIL 6 AM MST THURSDAY FOR NORTHERN HIGH
PLAINS, EASTERN GLACIER, WESTERN TOOLE, AND CENTRAL PONDERA.
HTTP://WWW.WEATHER.GOV/GREATFALLS
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