997
FXUS65 KMSO 210852
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
152 AM MST SAT DEC 21 2024
DISCUSSION
KEY MESSAGES:
- RISK FOR FREEZING RAIN ON SUNDAY AND MONDAY MORNINGS ACROSS
PORTIONS OF NORTHWEST AND WEST-CENTRAL MONTANA VALLEYS.
- MILD PACIFIC STORM TRACK CONTINUES INTO CHRISTMAS DAY.
- PROLONGED PERIOD OF MOUNTAIN SNOW FOLLOWING CHRISTMAS.
HIGH PRESSURE WILL CONTINUE TODAY AS A TROUGH OF LOW PRESSURE
MOVES ONSHORE IN THE PACIFIC NORTHWEST. THIS SYSTEM WILL KICK OFF
A WEEK OF UNSETTLED WEATHER ACROSS THE NORTHERN ROCKIES. NO
SYSTEM IN PARTICULAR WILL PACK MUCH OF A PUNCH AS TEMPERATURES
STAY MILD ENOUGH TO KEEP SNOW LEVELS ABOVE VALLEY FLOORS.
A SPLIT FLOW WEATHER PATTERN WILL PERSIST THROUGH MONDAY. TWO
PACIFIC TROUGHS STAND OUT, WITH THE FIRST SYSTEM ARRIVING TONIGHT
AND INTO SUNDAY MORNING. SNOW LEVELS WILL CLIMB ABOVE 4,500-5,000
FEET, INTRODUCING THE THREAT FOR POCKETS OF FREEZING RAIN ACROSS
THE VALLEYS OF NORTHWEST AND WEST-CENTRAL MONTANA. LIGHT TO
MODERATE SNOW WILL CONTINUE ACROSS MOUNTAIN RANGES THROUGH SUNDAY
MORNING, BRINGING ABOUT 3-8 INCHES OF ACCUMULATION. ANOTHER
SYSTEM ARRIVES SUNDAY NIGHT INTO MONDAY MORNING, FOLLOWING A
SIMILAR TREND, WITH VALLEY RAIN AND POCKETS OF FREEZING RAIN AND
HIGH ELEVATION MOUNTAIN SNOW. SNOW ACCUMULATIONS REMAIN MODEST.
THE OVERALL PATTERN BEGINS TO SHIFT ON TUESDAY, AS A DEEPER
TROUGH APPROACHES THE WEST COAST. SOUTHWESTERLY FLOW DURING THE
ONSET OF PRECIPITATION WILL KEEP SNOW LEVELS HIGH, RANGING FROM
4,500-5,500 FEET TUESDAY MORNING. A COLD FRONT WILL MOVE THROUGH
THE NORTHERN ROCKIES TUESDAY NIGHT INTO CHRISTMAS MORNING, WITH
SNOW LEVELS DROPPING TO 3,500 FEET. SNOW WILL ONCE AGAIN FOCUS
ACROSS THE MOUNTAINS, WITH LITTLE TO NO VALLEY ACCUMULATIONS.
GLOBAL ENSEMBLES CONTINUE TO ADVERTISE A PROGRESSIVE WESTERLY FLOW
FOLLOWING CHRISTMAS DAY, WITH SEVERAL PACIFIC SYSTEMS LEADING TO A
FAVORABLE PATTERN FOR MOUNTAIN SNOW. THIS IS SUPPORTED WELL BY THE
8-14 CLIMATE PREDICTION CENTERS HAZARD OUTLOOK, WHICH HAS THE
NORTHERN ROCKIES UNDER A MODERATE RISK (40-60%) FOR HEAVY SNOW BY
DECEMBER 28.
AVIATION
STABLE CONDITIONS WILL CONTINUE UNDER A RIDGE OF HIGH
PRESSURE THROUGH THIS AFTERNOON. CLEARING SKIES AND NARROW DEW
POINT DEPRESSIONS AT KGPI ARE INDICATING POTENTIAL FOR FOG TO
DEVELOP THIS MORNING. EXPECT INCREASING CLOUDS THIS AFTERNOON
AHEAD OF AN APPROACHING TROUGH OF LOW PRESSURE. A RAIN-SNOW MIX
WILL ARRIVE TONIGHT BY ABOUT 22/0300Z - 22/0400Z AT KGPI, KMSO,
KHRF, AND KSMN. PRECIPITATION WILL RESULT IN REDUCTIONS IN
VISIBILITY AND CEILING, AND WILL OBSCURE TERRAIN OVER ALL MOUNTAIN
RANGES OF THE NORTHERN ROCKIES.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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