499
FXUS65 KTFX 151646
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
946 AM MST SUN DEC 15 2024
KEY MESSAGES
- SNOWY START TO THE DAY ON SUNDAY WITH MOST AREAS SEEING LESS
THAN 2 INCHES, WITH UP TO 6 INCHES IN THE HIGHER TERRAIN OF THE
LITTLE AND BIG BELTS
- AFTER A FEW COOLER DAYS THROUGH TUESDAY, WARMER AIR SURGES BACK
IN ON WEDNESDAY, ALONG WITH GUSTY WINDS
- UPPER LEVEL RIDGING RETURNS AFTER WEDNESDAY, WITH WARMER
TEMPERATURES AND MOSTLY TRANQUIL CONDITIONS THROUGH THE WEEKEND
UPDATE
UPDATED FORECAST IS OUT. MAIN ADJUSTMENTS WERE TO END THE WINTER
WEATHER ADVISORY FOR AREAS WHERE THE SNOW HAS EXITED. SNOW STAYED
SOUTH OF THE HIGHWAY 2 CORRIDOR FROM CHESTER TO HARLEM, SO THE
ADVISORY WAS CANCELLED THERE. OVER THE WESTERN PORTIONS OF THE
CWA, MOST OF THE SNOWFALL HAS ENDED, EXCEPT IN THE ELK PARK AREA,
SO THE ADVISORIES WERE CANCELLED OVER THE WESTERN PORTIONS OF THE
CWA, EXCEPT ELK PARK WHERE THE ADVISORY CONTINUES UNTIL 11 AM.
SNOW CONTINUES TO FALL THIS MORNING AROUND MONARCH/JUDITH
GAP/BRIDGER/BIG SKY AREA, SO THAT ADVISORY CONTINUES UNTIL LATE
AFTERNOON. SNOWFALL SHOULD BE LIGHTER THE REST OF TODAY, WITH
ANOTHER INCH OR TWO POSSIBLE IN THE ADVISORY AREAS. OTHERWISE,
TEMPERATURES WILL NOT RISE MUCH THE REST OF TODAY, WITH MOST AREAS
SEEING A CLOUD COVER UNTIL LATE AFTERNOON. BRUSDA
DISCUSSION
/ISSUED 358 AM MST SUN DEC 15 2024/
- METEOROLOGICAL OVERVIEW:
AN UPPER LEVEL TROUGH PUSHING INTO THE WESTERN US TODAY HAS
BROUGHT A PLUME OF MOISTURE INTO NORTH CENTRAL AND SOUTHWESTERN
MONTANA, WHICH HAS BEEN VISIBLE MOST OF THE OVERNIGHT HOURS ON
RADAR. WHILE MOST OF THIS PRECIPITATION HAS NOT YET REACHED THE
GROUND AS OF 3 AM, AN AREA OF HEAVIER PRECIPITATION MOVING IN FROM
WESTERN MONTANA/NORTHERN IDAHO WILL RESULT IN A FEW AREAS OF LIGHT
TO MODERATE PRECIPITATION, SOME OF WHICH WILL EVENTUALLY FALL AS
SNOW EVEN IN THE LOWER ELEVATIONS AS THIS PRECIPITATION MOVES IN
ALONG WITH SOME COOLER AIR FROM THE NORTH. BEHIND THIS SYSTEM,
UPPER LEVEL RIDGING WILL BRIEFLY MOVE INTO THE AREA AS AN UPPER
LEVEL LOW MOVES TOWARDS AND DISSIPATES JUST OFF THE WESTERN US
COAST. WHILE THIS SYSTEM ITSELF WILL NOT BE ABLE TO PUSH INLAND,
IT WILL SEND A BIT OF MOISTURE OUR WAY AS AN UPPER LEVEL RIDGE
BEGINS TO BUILD BACK IN ACROSS THE WESTERN US, ALLOWING FOR A
WIDESPREAD LIGHT SNOWFALL TO PRECEDE THE ARRIVAL OF WARMER AIR AND
WINDS ON WEDNESDAY. UPPER LEVEL RIDGING WILL BECOME THE MAIN
FEATURE OF OUR WEATHER AFTER THURSDAY, RESULTING IN WARM AND
LARGELY TRANQUIL WEATHER FOR THE END OF THE WEEK.
- FORECAST CONFIDENCE & SCENARIOS:
OVERALL, CONFIDENCE IN THE OVERALL WEATHER PATTERN IS RELATIVELY
HIGH THROUGH THE END OF THE WEEK, WITH ALL 4 CLUSTERS FROM WPC’S
CLUSTER ANALYSIS TOOL SHOWING LARGELY THE SAME IDEA (WITH THE
USUAL MINOR DIFFERENCES IN TIMING/STRENGTH OF FEATURES). SO MOST
OF THE UNCERTAINTY WILL BE IN THE DETAILS, WHICH IS EVIDENT EVEN
THIS MORNING. MODELS THIS MORNING REMAIN RELATIVELY CERTAIN THAT
PORTIONS OF THE AREA WILL SEE SOME LIGHT TO MODERATE SNOWFALL WITH
JUST SOME MINOR DIFFERENCES IN TIMING AND INTENSITY. OVERALL, THE
MOST LIKELY SCENARIO THIS MORNING IS SOME LIGHT TO MODERATE
SNOWFALL ALONG AND SOUTH OF A LINE FROM GREAT FALLS TO LEWISTOWN,
LARGELY FOCUSED ALONG AN AREA OF CONVERGENCE ALOFT AT 700 MB
(ABOUT 6000 FEET ABOVE THE GROUND). HOWEVER, THERE ARE SOME
INDICATIONS THAT WE MAY GET SOME PRECIPITATION TO DEVELOP ALONG
THE LEADING EDGE OF A COOLER AIR MASS COMING IN FROM THE NORTH,
WITH ABOUT 25% OR SO OF THE MODELS SUGGESTING THIS. THIS SCENARIO
WOULD RESULT IN SNOWFALL BEING A BIT MORE WIDESPREAD ACROSS THE
PLAINS, THOUGH EVEN IF THIS WERE TO OCCUR SNOWFALL AMOUNTS WOULD
GENERALLY BE AN INCH OR LESS.
AFTER COOLER, BUT FAIRLY NON-EVENTFUL WEATHER DAYS MONDAY AND
TUESDAY, A QUICKLY BUILDING UPPER LEVEL RIDGE WILL SEND A STRONG
WARM FRONT THROUGH SOUTHWESTERN AND CENTRAL MONTANA, WITH A BIT OF
OVERRUNNING PRECIPITATION ALONG AND AHEAD OF IT. WHILE ANY
PRECIPITATION WILL GENERALLY BE LIGHT (AND MOSTLY SNOW), THE
BIGGER STORY WEDNESDAY WILL BE THE WINDS, WITH PROBABILITIES
ALREADY STARTING TO CREEP (AND EVEN EXCEED) 50% FOR GUSTS OVER 55
MPH IN THE USUALLY WINDY LOCATIONS ALONG THE ROCKY MOUNTAIN FRONT
AND THE NORTH SLOPES OF THE LITTLE BELT AND SNOWY MOUNTAINS,
INCLUDING JUDITH GAP. WHILE WE ARE STARTING TO SEE THE CONFIDENCE
FOR HIGH WIND WATCHES, IT IS STILL JUST A BIT EARLY FOR THESE
PRODUCTS TO BE ISSUED SINCE WE ARE BEYOND 72 HOURS FROM THE EVENT,
SO I WILL HOLD OFF ON ANY WATCHES FOR NOW WITH THE EXPECTATION
THAT THEY WILL BE ISSUED IN THE NEXT 12-24 HOURS. THIS COULD WIND
UP BEING A FAIRLY STRONG WIND EVENT, WITH SOME AREAS SEEING A
GREATER THAN 10% CHANCE OF SEEING A WIND GUST OVER 70 MPH, SUCH AS
CUT BANK AND GREAT FALLS.
BEYOND THE WIND EVENT ON WEDNESDAY AND EARLY THURSDAY MORNING,
CONFIDENCE IS VERY HIGH IN AN UPPER LEVEL RIDGE BUILDING INTO THE
AREA, WHICH WILL BRING A RETURN TO WELL ABOVE AVERAGE TEMPERATURES
AND GENERALLY TRANQUIL WEATHER. LUDWIG
AVIATION
15/12Z TAF PERIOD
WHILE MOSTLY VFR CONDITIONS ARE EXPECTED OVER THE TAF PERIOD, A
FEW PERIODS OF MVFR TO IFR CONDITIONS ARE POSSIBLE AT KBZN, KEKS,
KHLN, KGTF, AND KLWT THROUGH THIS AFTERNOON AS A WEATHER SYSTEM
MOVES THROUGH. FOR THE MOST PART, EXPECT MVFR CONDITIONS TO BE
BRIEF, WITH SOME INTERMITTENT LOW CIGS AND PERIODS OF RA AND SN
FALL AT THE MENTIONED SITES, WITH THE BEST CHANCE FOR PROLONGED
IFR CONDITIONS EXPECTED AT KLWT WHERE SNOW IS LIKELY TO BE MOST
INTENSE AND PERSISTENT THROUGH THE MORNING HOURS. AFTER NOON/19Z,
EXPECT CLOUDS TO LIFT AS SNOW ENDS, BRINGING A RETURN TO VFR
CONDITIONS FOR THE EVENING AND OVERNIGHT. LUDWIG
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION
WEATHER AND HAZARD INFORMATION.
PRELIMINARY POINT TEMPS/POPS
GTF 40 20 35 19 / 80 0 30 60
CTB 37 15 30 11 / 10 0 20 60
HLN 39 21 33 23 / 80 0 60 60
BZN 37 13 32 21 / 80 0 50 60
WYS 29 5 25 13 / 90 20 90 90
DLN 34 14 33 19 / 50 0 30 30
HVR 39 13 27 9 / 10 0 0 60
LWT 37 15 34 19 / 80 0 20 70
TFX WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR BIG
BELT, BRIDGER AND CASTLE MOUNTAINS-GALLATIN AND MADISON COUNTY
MOUNTAINS AND CENTENNIAL MOUNTAINS-LITTLE BELT AND HIGHWOOD
MOUNTAINS.
WINTER WEATHER ADVISORY UNTIL 11 AM MST THIS MORNING FOR ELKHORN
AND BOULDER MOUNTAINS.
HTTP://WWW.WEATHER.GOV/GREATFALLS
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