Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 182158
AFDMSO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
258 PM MST THU DEC 18 2014

.DISCUSSION...

SNOW CURRENTLY FALLING IN WESTERN MONTANA WILL BE DECREASING THIS
EVENING AS DRIER AIR MOVES IN. LIGHT ACCUMULATIONS ARE STILL
POSSIBLE FOR COUNTIES ALONG THE DIVIDE.

THE BREAK IN PRECIPITATION WILL BE SHORT-LIVED AS THE NEXT IN A
SERIES OF SYSTEMS MOVES INTO NORTH CENTRAL IDAHO AND WESTERN
MONTANA FRIDAY MORNING. PASSES SUCH AS LOOKOUT, LOLO, LOST TRAIL,
AND MARIAS WILL BE THE MOST AFFECTED, AS THEY ARE EXPECTED TO SEE
2 TO 4 INCHES OF SNOW. TRAVELERS OVER THESE PASSES SHOULD LEAVE
ENOUGH TIME AND PREPARE FOR SLICK/SLUSHY CONDITIONS. THE FLATHEAD,
MISSOULA, AND BITTERROOT VALLEYS SHOULD BE WARM ENOUGH FOR
PRECIPITATION TO MELT AND FALL AS LIGHT RAIN.

A VERY MOIST ATMOSPHERIC RIVER EVENT STILL LOOKS LIKELY BEGINNING
LATE SATURDAY THROUGH EARLY MONDAY ACROSS THE REGION, WITH
HEAVIEST PRECIPITATION AMOUNTS EXPECTED FOR CENTRAL IDAHO, THE BOB
MARSHALL THROUGH THE GLACIER REGION, AND MOUNTAIN PASSES ALONG THE
MONTANA/IDAHO BORDER. THE EVENT WILL BEGIN AS HEAVY WET SNOW WITH
COLDER AIR IN PLACE SATURDAY, BUT WILL LIKELY TRANSITION OVER TO
HEAVY RAIN SUNDAY WITH SNOW LEVELS RISING FROM THE SOUTHWEST TO
THE NORTHEAST TO AROUND 5000-6000 FT. IT IS STILL UNCERTAIN HOW
QUICKLY THE SNOW LEVELS WILL INCREASE, WHICH COULD DRAMATICALLY
CHANGE THE AMOUNT OF SNOW ACCUMULATIONS EXPECTED FOR MOUNTAIN
PASSES. LOLO, LOOKOUT, LOST TRAIL, AND MARIAS PASSES COULD SEE 4
TO 12 INCHES OF WET SNOW. ONCE THE SNOW SWITCHES OVER TO HEAVY
RAIN, THIS COULD RESULT IN VERY SLUSHY AND SLIPPERY TRAVEL FOR
UNCLEARED ROADS, IN ADDITION TO A RISK OF ROCK AND MUD SLIDES
PARTICULARLY FOR HIGHWAY 12 AND 14 IN IDAHO. PONDING OF WATER ON
ROADWAYS COULD ALSO BE POSSIBLE FOR RELATIVELY LOW-LYING AREAS AND
SHOULD BE AVOIDED DURING TRAVEL.

THE FLOW RETURNS TO MORE NORTHWESTERLY TUESDAY INTO WEDNESDAY,
WHICH WILL ALLOW SNOW LEVELS TO LOWER ONCE AGAIN, AT LEAST TO
PASS LEVELS. HOWEVER DURING THIS TIME FRAME THE HEAVIEST
PRECIPITATION SHOULD BE ON THE DOWNWARD TREND. FORECAST MODELS
CONTINUE TO SHOW A MUCH COLDER PATTERN SETTING UP AROUND
CHRISTMAS, PARTICULARLY FOR THE WEEKEND FOLLOWING. HOWEVER,
CONFIDENCE IN POSSIBLE SNOW FOR THE CHRISTMAS HOLIDAY REMAINS LOW.
THERE ARE SIGNIFICANT DIFFERENCES BETWEEN FORECAST MODELS IN TERMS
OF PRECIPITATION, SO STAY TUNED!

&&

.AVIATION...LIGHT SNOW SHOWERS AT KGPI AND THROUGHOUT THE AREA WILL
COME TO AN END THIS EVENING. LOW CLOUD DECKS AND TERRAIN
OBSCURATIONS WILL PERSIST ACROSS THE REGION. WINDS REMAIN LIGHT AS
THE NEXT ROUND OF PRECIPITATION BEGINS TO MOVE IN FROM THE WEST
TOMORROW MORNING. KGPI WILL AGAIN BE THE FIRST TO SEE MEASURABLE
LIGHT RAIN BEGINNING AROUND 19/1500Z, AND LATER IN THE DAY FOR
OTHER TAF SITES.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
ID...NONE.
&&

$$


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