420
FXUS65 KTFX 211133
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
433 AM MST SAT DEC 21 2024
AVIATION SECTION UPDATED.
KEY MESSAGES
- COOL TEMPERATURES CONTINUE TO BE TRAPPED IN THE MILK RIVER
VALLEY TODAY AND TONIGHT.
- FREEZING RAIN TONIGHT IN THE HAVRE AND HARLEM AREAS.
- WINDY CONDITIONS AT TIMES OVER THE PLAINS OF NORTH CENTRAL
MONTANA TONIGHT THROUGH MONDAY.
- ABOVE NORMAL TEMPERATURES EXPECTED ALL OF NEXT WEEK.
- LIGHT SNOW POSSIBLE CHRISTMAS EVE INTO CHRISTMAS DAY OVER
SOUTHWEST MONTANA.
DISCUSSION
/ISSUED 401 AM MST SAT DEC 21 2024/
- METEOROLOGICAL OVERVIEW:
AN UPPER LEVEL RIDGE OF HIGH PRESSURE WILL MOVE EASTWARD ACROSS
MT TODAY. HOWEVER, COLD AIR WILL REMAIN TRAPPED AT LOWER LEVELS
AROUND HARLEM/HAVRE. AN UPPER LEVEL DISTURBANCE WILL MOVE EASTWARD
ACROSS THE CWA TONIGHT, AS THE UPPER LEVEL RIDGE MOVES TO OUR
EAST. STRONG DOWNSLOPE WINDS WILL DEVELOP JUST EAST OF THE DIVIDE.
OVERALL WIND SPEEDS ARE EXPECTED TO REMAIN JUST BELOW WARNING
CRITERIA. EXPECT RAIN/SNOW IN THE MOUNTAINS ALONG THE DIVIDE AND
THEN A MIX OF FREEZING RAIN/SNOW IN THE HAVRE/HARLEM AREAS. LIQUID
AMOUNTS UP TO A 0.10 INCHES ARE POSSIBLE IN THE HAVRE/HARLEM
AREAS. WITH COLD AIR TRAPPED NEAR THE SURFACE, FREEZING RAIN IS
EXPECTED IN THIS AREA, THUS A WINTER WEATHER ADVISORY HAS BEEN
ISSUED FOR THE HAVRE/HARLEM AREAS.
THE UPPER LEVEL DISTURBANCE EXITS THE CWA ON SUNDAY MORNING, WITH
THE FORECAST MODELS COMING INTO BETTER AGREEMENT FOR MUCH OF NEXT
WEEK. OVERALL, ABOVE NORMAL TEMPERATURES ARE EXPECTED ALL OF NEXT
WEEK. THE BEST CHANCE FOR ANY PRECIPITATION LOOKS TO BE CHRISTMAS
EVE/CHRISTMAS DAY OVER SOUTHWEST MT. SNOW AMOUNTS ARE FORECAST TO
BE LESS THAN AN INCH AT LOWER ELEVATIONS OF SOUTHWEST MT, WITH 2
TO 5 INCHES POSSIBLE IN THE MOUNTAINS ACROSS ZONE 330. A SECOND
UPPER LEVEL DISTURBANCE WILL MOVE THROUGH THE FAR SOUTHERN
PORTIONS OF THE CWA THU INTO FRIDAY, MAINLY AFFECTING JUST THE
WEST YELLOWSTONE AREA.
- FORECAST CONFIDENCE & SCENARIOS:
THE FORECAST MODELS ARE SHOWING A HIGH POTENTIAL FOR FREEZING
RAIN TONIGHT IN THE HAVRE/HARLEM AREAS, WITH WARM AIR ALOFT AND
TEMPERATURES NEAR/BELOW FREEZING AT THE SURFACE. THIS WILL BE A
QUICK SYSTEM, WITH MOST OF THE THE FREEZING RAIN FALLING IN JUST A
FEW HOURS.
FOR CHRISTMAS EVE/CHRISTMAS DAY, THE PROBABILITY OF 2 INCHES OF
SNOWFALL IS ABOUT 60 PERCENT IN THE MOUNTAINS AROUND BIG SKY/WEST
YELLOWSTONE AREA. FOR THU/FRI...THE WEST YELLOWSTONE AREA HAS
AGAIN ABOUT A 60 PERCENT CHANCE FOR 2 INCHES OR MORE OF SNOWFALL.
BRUSDA
AVIATION
21/12Z TAF PERIOD
VFR CONDITIONS ARE EXPECTED TO CONTINUE OVER NORTH CENTRAL,
CENTRAL, AND SOUTHWEST MONTANA THROUGH AT LEAST 22/12Z.
A HIGH PRESSURE RIDGE OVER THE AREA WILL ONLY ALLOW PASSING MID-
AND HIGH-LEVEL CLOUDINESS THROUGH AROUND 00Z. A DISTURBANCE FROM
THE PACIFIC NORTHWEST WILL THEN SPREAD INCREASED WESTERLY WINDS
EAST ACROSS THE AREA, CAUSING MOUNTAIN WAVE TURBULENCE AND LOW
LEVEL WIND SHEAR, AS WELL BRINGING INCREASING CLOUDINESS AND
MAINLY MOUNTAIN PRECIPITATION. HOWEVER, THE RELATIVELY WARM
PRECIPITATION MOVING OVER COLD AIR TRAPPED OVER THE NORTHEAST
PORTION OF NORTH CENTRAL MONTANA (INCLUDING KHVR) COULD PRODUCE A
PERIOD OF FREEZING DRIZZLE/RAIN THERE, MAINLY BETWEEN 06Z AND
12Z, POSSIBLY WITH PERIODS OF MVFR CONDITIONS. -COULSTON
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION
WEATHER AND HAZARD INFORMATION.
PRELIMINARY POINT TEMPS/POPS
GTF 55 37 49 32 / 0 20 0 0
CTB 51 35 44 27 / 0 20 0 0
HLN 48 31 45 29 / 0 30 0 0
BZN 49 27 45 25 / 0 30 0 0
WYS 38 16 32 19 / 0 30 20 30
DLN 46 25 42 26 / 0 10 0 0
HVR 38 26 43 23 / 0 80 20 0
LWT 56 33 45 27 / 0 20 0 0
TFX WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 8 AM MST SUNDAY
FOR HILL COUNTY-NORTHERN BLAINE COUNTY.
HTTP://WWW.WEATHER.GOV/GREATFALLS
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