159
FXUS65 KTFX 260355
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
855 PM MST SAT JAN 25 2025
KEY MESSAGES
- COLD TEMPERATURES AND PATCHY DENSE VALLEY FOG ACROSS SOUTHWEST
MONTANA TONIGHT INTO EARLY SUNDAY MORNING.
- DRY AND MILDER CONDITIONS DEVELOP AND PERSIST THROUGH MUCH OF
THE WEEK AHEAD WITH DELAYED WARMING IN SOME SOUTHWEST MONTANA
VALLEYS.
- THE NEXT CHANCE FOR WIDESPREAD PRECIPITATION AND A TURN TO
COLDER TEMPERATURES IS EXPECTED TO DEVELOP NEXT WEEKEND.
UPDATE
PATCHY DENSE FOG IS DEVELOPING ALONG THE INTERSTATE 90/HIGHWAY
287 CORRIDORS BETWEEN BOZEMAN AND HELENA THIS EVENING AND IS
EXPECTED TO EXPAND IN COVERAGE LATER TONIGHT INTO EARLY SUNDAY
GIVEN STRENGTHENING VALLEY INVERSIONS. IN LIGHT OF THIS, A DENSE
FOG ADVISORY HAS BEEN SENT OUT TO COVER THE EXPECTED IMPACTS,
INCLUDING VARIABLE VISIBILITY REDUCTIONS DOWN TO A QUARTER MILE
AND SLIPPERY SPOTS ON ROADWAYS DUE TO FROST DEPOSITION. THE
ADVISORY RUNS THROUGH 11 AM MST SUNDAY. OTHERWISE, THE PRIMARY
CONCERN WILL BE COLD TEMPERATURES IN SOUTHWEST MONTANA WHERE NO
CHANGES WERE MADE TO TONIGHT'S COLD WEATHER ADVISORIES. - RCG
DISCUSSION
/ISSUED 149 PM MST SAT JAN 25 2025/
- METEOROLOGICAL OVERVIEW:
A SOMEWHAT STAGNANT BUT OVERALL MILD AND DRY WEATHER PATTERN
DEVELOPS THROUGH MUCH OF THE WEEK AHEAD AS A LARGE UPPER LEVEL RIDGE
CENTERED OFFSHORE OF THE PACIFIC COAST GRADUALLY TILTS EAST INTO
WESTERN CANADA AND THE NW US WHILE TROUGHING UNDERCUTTING THE RIDGE
ACROSS THE SW US SETS UP SHORT TERM BLOCKING PATTERN. NORTHERLY FLOW
ALOFT DOWNSTREAM OF THE UPPER RIDGE ACROSS THE NORTHERN ROCKIES AND
MT WILL TRANSITION TO WESTERLY BY THE MIDDLE OF NEXT WEEK WITH
RELATIVELY LOW MID TO UPPER LEVEL WIND SPEEDS THROUGH AT LEAST
THURSDAY BEFORE FLOW INCREASES AS THE WEAKENING RIDGE AXIS SHIFTS
EAST OF THE AREA BY THE END OF THE WORK WEEK.
AT THE SURFACE, HIGH PRESSURE AND A COLD AIRMASS CENTERED OVER SW MT
TODAY WILL GRADUALLY WEAKEN ACROSS THE PLAINS OVER THE NEXT SEVERAL
DAYS BUT REMAIN ESTABLISHED ACROSS SW MT AND THE INTERIOR WESTERN US
INTO NEXT WEEK. TEMPERATURES GRADUALLY WARM THROUGH MUCH OF THE
UPCOMING WEEK, REACHING SEASONAL LEVELS IN MOST AREAS BY MONDAY AND
ABOVE AVERAGE BY THE MIDDLE OF NEXT WEEK WITH SLOWER WARMING ACROSS
SW MT. LOW PRESSURE SYSTEMS MOVING SOUTHEAST ACROSS CENTRAL CANADA
WILL INCREASE THE PRESSURE GRADIENT ACROSS THE ROCKIES WITH BREEZY
TO LOCALLY WINDY CONDITIONS DEVELOPING ACROSS THE NORTH-CENTRAL MT
PLAINS, BUT ANY POTENTIAL FOR STRONGER WINDS LOOKS TO BE LIMITED TO
AREAS ALONG THE IMMEDIATE EAST SLOPES OF THE ROCKIES LATER NEXT
WEEK.
- FORECAST CONFIDENCE & SCENARIOS:
SW MT TEMPERATURES:
A COLD ADVISORY REMAINS IN EFFECT FOR PORTIONS OF SW MT WHERE
OVERNIGHT LOW TEMPERATURES ARE EXPECTED TO REACH THE TEENS BELOW
ZERO IN SOME VALLEYS TO AS LOW AS 20 BELOW TO 30 BELOW ZERO IN
TYPICALLY COLDER LOCATIONS LIKE ELK PARK, THE BIG HOLE AND
CENTENNIAL VALLEYS AND THE WEST YELLOWSTONE AREA. WINDS ARE
EXPECTED TO BE LIGHT (LESS THAN 10 MPH) IN THESE AREAS CREATING
ONLY SLIGHTLY COLDER WIND CHILLS.
COLD SURFACE TEMPERATURES/SNOWCOVER AND WARMING/LIGHT FLOW ALOFT
BENEATH THE INCOMING UPPER LEVEL RIDGE OVER THE NEXT SEVERAL DAYS
ARE LIKELY TO RESULT IN A STRONG TEMPERATURE INVERSION ABOVE SW MT
VALLEYS, WITH COLDEST AIR TYPICALLY LINGERING THE LONGEST IN AREAS
FROM THE GALLATIN VALLEY NORTH THOUGH THE CANYON FERRY AREA INTO THE
HELENA VALLEY. DAYTIME TEMPERATURES WERE BLENDED TO THE COLDER 25TH
PERCENTILE OF ENSEMBLE MODEL GUIDANCE IN THESE AREAS THROUGH MONDAY
BUT COLDER TEMPERATURES COULD LINGER LATER INTO NEXT WEEK IN THIS
SITUATION.
CHANGE COMING NEXT WEEKEND:
LONGER RANGE MODEL ENSEMBLES REMAIN IN GOOD AGREEMENT ON A LARGER
SCALE PATTERN CHANGE DEVELOPING NEXT WEEKEND WITH AN UPPER LEVEL
TROUGH DEEPENING ACROSS WESTERN CANADA INTO THE NW US. THERE ARE
SOME DIFFERENCES IN HOW FAR SOUTH AND WEST THE TROUGH AMPLIFIES, BUT
OVER 60% OF MODEL ENSEMBLES SUPPORT A SCENARIO THAT WOULD ALLOW AN
ARCTIC AIRMASS TO SLIDE SOUTH FROM NW CANADA INTO THE REGION,
RESULTING IN MUCH COLDER TEMPERATURES AS WELL AS WIDESPREAD
PRECIPITATION. HOENISCH
AVIATION
26/00Z TAF PERIOD
RIDGING ALOFT BECOMES MORE ESTABLISHED OVER THE NORTHERN ROCKIES FOR
MOSTLY CLEAR SKIES AND VFR CONDITIONS; HOWEVER, THERE WILL BE THE
POTENTIAL FOR PATCHY DENSE FOG DEVELOPMENT IN THE WIND PROTECTED
SOUTHWEST VALLEYS TONIGHT INTO EARLY SUNDAY, INCLUDING THE KBZN AND
KHLN TERMINALS. CURRENT PROBABILISTIC GUIDANCE FOR VISIBILITY
REDUCTIONS BELOW A HALF MILE ARE BELOW 20%, BUT STRENGTHENING VALLEY
INVERSIONS INTERACTING WITH LINGERING SURFACE MOISTURE DOES CREATE A
FAVORABLE ENVIRONMENT FOR FOG DEVELOPMENT. SOUTHWESTERLY WINDS
INCREASE TO AROUND 20 TO 30 KTS OVER THE PLAINS BY SUNDAY AFTERNOON
WHILE REMAINS LIGHT AND VARIABLE OVER THE SOUTHWEST. - RCG
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION
WEATHER AND HAZARD INFORMATION.
PRELIMINARY POINT TEMPS/POPS
GTF 4 27 18 37 / 0 0 0 0
CTB 9 33 21 38 / 0 0 0 0
HLN -5 17 6 29 / 0 0 0 0
BZN -19 16 1 29 / 0 0 0 0
WYS -30 22 -10 31 / 0 0 0 0
DLN -7 20 5 30 / 0 0 0 0
HVR 8 27 18 37 / 0 0 0 0
LWT 4 31 18 39 / 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.
DENSE FOG ADVISORY UNTIL 11 AM MST SUNDAY FOR CANYON FERRY AREA-
GALLATIN VALLEY-HELENA VALLEY-MISSOURI HEADWATERS.
HTTP://WWW.WEATHER.GOV/GREATFALLS
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