078
FXUS65 KTFX 160439
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
939 PM MST SUN DEC 15 2024
AVIATION SECTION UPDATED.
KEY MESSAGES
- NEXT ROUND OF IMPACTFUL SNOWFALL BEGINS MONDAY AFTERNOON AND
ENDS ON TUESDAY MORNING.
- STRONG WINDS ARE LOOKING VERY LIKELY WEDNESDAY ALONG THE EAST
SLOPES OF THE ROCKIES.
- DRIER AND WARMER CONDITIONS EXPECTED BY THE END OF THE WEEK AND
CONTINUING INTO NEXT WEEKEND.
UPDATE
/ISSUED 832 PM MST SUN DEC 15 2024/
MADE SOME MINOR ADJUSTMENTS TO THE PERIOD OF THE FORECAST
COVERING THE REST OF TONIGHT INTO MONDAY MORNING.
WEB CAMERAS INDICATE THAT LIGHT SNOW SHOWERS CONTINUE TO FALL IN
THE MOUNTAIN AREAS OF SOUTHWEST MONTANA FROM NORTHWEST BEAVERHEAD
COUNTY EAST- SOUTHEAST INTO THE MADISON AND GALLATIN MOUNTAINS.
HAVE THEREFORE INCREASED THE CHANCES THERE THROUGH THE REMAINDER
OF THE EVENING.
OTHER FORECAST ENHANCEMENT WAS TO INCREASE AREA AND COVERAGE OF
LOW CLOUDS AND FOG OVER THE PLAINS ALONG THE CANADIAN BORDER.
CALGARY AND MEDICINE HAT IN ALBERTA HAVE BEEN REPORTING REDUCED
VISIBILITY AND LOW CEILINGS FOR MUCH OF THIS AFTERNOON AND
EVENING BEHIND A WEAK FRONTAL BOUNDARY CURRENTLY ALONG THE
CANADIAN BORDER. THIS BOUNDARY IS FORECAST TO SLOWLY SAG SOUTH
OVERNIGHT TO A LINE FROM CUT BANK TO NORTHERN FERGUS COUNTY. THIS
SHOULD HELP SPREAD THE LOW CLOUDS AND FOG AT LEAST INTO THE CUT
BANK AND HAVRE AREAS. HOWEVER, CEILINGS AND VISIBILITIES IN
ALBERTA ARE NOT SIGNIFICANTLY LOW, SO AM NOT ANTICIPATING A NEED
FOR A DENSE FOG ADVISORY AT THIS TIME. -COULSTON
DISCUSSION
/ISSUED 832 PM MST SUN DEC 15 2024/
- METEOROLOGICAL OVERVIEW:
AN UPPER LEVEL TROF IS EXITING THE CWA THIS AFTERNOON, RESULTING
IN THE WIDESPREAD LIGHT SNOW FROM EARLIER TODAY TO DIMINISH. THUS
ALL WINTER STATEMENTS THAT WERE IN EFFECT FOR TODAY HAVE NOW
ENDED. SKIES WILL BE MOSTLY CLOUDY TONIGHT, BUT A FEW BREAKS COULD
ALLOW FOR SOME PATCHY FOG TO DEVELOP OVER SOUTHWEST MT AND ALSO
OVER THE NORTHERN PORTIONS OF HILL/BLAINE COUNTIES. ON MONDAY, THE
NEXT UPPER LEVEL TROF WILL MOVE INTO WESTERN MT BY THE LATE
AFTERNOON HOURS. THIS WILL RESULT IN ANOTHER ROUND OF LIGHT SNOW
OVER A GOOD PORTION OF THE CWA. WINTER WEATHER STATEMENTS HAVE
BEEN ISSUED FOR THE MOST LIKELY AREAS TO RECEIVE A FEW INCHES OR
MORE OF SNOWFALL WITH THIS EVENT.
MOST OF THE SNOWFALL DIMINISHES BY TUESDAY MORNING, BUT SCATTERED
SNOW SHOWERS ARE LIKELY TO CONTINUE INTO WEDNESDAY FOR MOUNTAIN
AREAS. BY WEDNESDAY AFTERNOON, A STRONG WESTERLY FLOW DEVELOPS
ALOFT. THIS WILL RESULT IN THE POTENTIAL FOR STRONG WINDS ALONG
THE EAST SLOPES OF THE ROCKIES AND ACROSS CENTRAL MT. HIGH WIND
STATEMENTS WILL LIKELY BE NEEDED FOR THIS EVENT.
AN UPPER LEVEL RIDGE OF HIGH PRESSURE IS EXPECTED TO BUILD OVER
THE CWA BY THE END OF THE WEEK AND INTO THE WEEKEND. THIS WILL
RESULT IN MOSTLY DRY CONDITIONS, ALONG WITH MILD TEMPERATURES
MOVING INTO THE CWA FOR LATE DECEMBER.
- FORECAST CONFIDENCE & SCENARIOS:
SNOWFALL FOR MONDAY AFTERNOON AND TUESDAY MORNING WILL BE MOST
IMPACTFUL OVER THE NORTHERN ROCKY MOUNTAIN FRONT AND THEN ACROSS
THE MOUNTAIN AREAS OF CENTRAL MT AND SOUTHWARD THROUGH THE
BRIDGER, BIG SKY AND WEST YELLOWSTONE AREAS. SNOWFALL AMOUNTS OF
2 TO 4 INCHES ARE LIKELY IN MANY OF THESE AREAS, WITH ISOLATED
HIGHER AMOUNTS AT RIDGE TOPS. THE PROBABILITY OF 1 INCH OF
SNOWFALL AT LOWER ELEVATIONS IS GENERALLY LESS THAN 30 PERCENT,
SO NO WINTER STATEMENT IS PLANNED FOR AT THIS TIME. HOWEVER, THE
SNOWFALL WILL IMPACT THE EVENING RUSH HOUR ON MONDAY. IF SNOW
AMOUNTS INCREASE A BIT, THERE IS THE POTENTIAL A WINTER STATEMENT
MIGHT BE NEEDED FOR SOME LOWER ELEVATION LOCATIONS ON MONDAY.
THE NEXT MAIN CONCERN IS THE POTENTIAL FOR STRONG WINDS ON
WEDNESDAY. RIGHT NOW THERE IS AN 80 PERCENT CHANCE OR HIGHER OF
WINDS OVER 60 MPH IN THE CUT BANK AND BROWNING AREAS BY WEDNESDAY
EVENING. THUS HIGH WIND STATEMENTS ARE LOOKING LIKELY FOR THIS
AREA. OVER CENTRAL MT, THE PROBABILITY IS 70 PERCENT FOR WINDS
OVER 58 MPH. THE NORTHERN ROCKIES ALSO HAVE OVER AN 80 PERCENT
CHANCE OF WIND GUSTS OVER 75 MPH, THUS THIS IS LOOKING LIKE A
RATHER STRONG WIND EVENT. BRUSDA
AVIATION
16/06Z TAF PERIOD
A FEW SNOW SHOWERS LINGER ACROSS THE SW MT MOUNTAINS THIS EVENING
WITH LOCAL MOUNTAIN OBSCURATION PERHAPS SOME VERY BRIEF VIS/CIG
REDUCTIONS AT KEKS BUT OTHERWISE CLOUDS DECREASE THROUGH TONIGHT
WITH VFR CONDITIONS PREVAILING AT MOST TERMINALS THROUGH MONDAY
MORNING. A FRONTAL BOUNDARY MOVING SOUTH FROM AB WILL SHIFT WINDS
TO THE NW AT KCTB AND KHVR LATER TONIGHT WITH SOME POTENTIAL FOR
LOW CLOUDS MOVING INTO THESE TERMINALS FOLLOWING THE FRONTAL
PASSAGE. HI-RESOLUTION MODEL GUIDANCE HAS 30-50% CHANCE FOR
CEILINGS LESS THAN 3000FT AT KHVR BUT LESS THAN 30% CHANCE FOR
KCTB. CLOUDS INCREASE AGAIN ON MONDAY AS THE NEXT WEATHER SYSTEM
MOVES IN FROM THE WEST WITH LIGHT SNOW DEVELOPING FROM SOUTH TO
NORTH ACROSS THE AREA MONDAY AFTERNOON THROUGH MONDAY EVENING.
HOENISCH
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION
WEATHER AND HAZARD INFORMATION.
PRELIMINARY POINT TEMPS/POPS
GTF 20 36 21 32 / 0 30 70 40
CTB 15 30 13 22 / 0 10 60 30
HLN 20 33 23 38 / 10 70 70 40
BZN 14 33 21 37 / 10 60 70 40
WYS 6 26 15 29 / 20 90 90 80
DLN 15 34 20 37 / 20 40 30 20
HVR 13 28 12 22 / 10 0 60 60
LWT 15 34 19 32 / 0 20 80 70
TFX WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY FROM 2 PM MONDAY TO 9 AM MST TUESDAY FOR
BIG BELT, BRIDGER AND CASTLE MOUNTAINS-EAST GLACIER PARK REGION-
GALLATIN AND MADISON COUNTY MOUNTAINS AND CENTENNIAL MOUNTAINS-
LITTLE BELT AND HIGHWOOD MOUNTAINS.
HTTP://WWW.WEATHER.GOV/GREATFALLS
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