826
FXUS65 KMSO 221054
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
354 AM MST TUE JAN 22 2019
DISCUSSION
RECENT SNOW HAS COMBINED WITH A MELT-REFREEZE
SITUATION ON AREA ROADWAYS, MAKING FOR VERY SLICK CONDITIONS
ACROSS MUCH OF WEST CENTRAL AND NORTHWEST MONTANA THIS MORNING.
EVEN THOUGH PRECIPITATION HAS ENDED, PLEASE USE CAUTION WHILE
TRAVELING THIS MORNING.
THE REGION'S NEXT ROUND OF WINTRY WEATHER WILL BEGIN TONIGHT, AS
MOISTURE MOVES INTO THE NORTHERN ROCKIES FROM THE WEST. IN DOING
SO, MODERATE TO HEAVY SNOWFALL WILL IMPACT MOUNTAINOUS TERRAIN
ALONG THE ID/MT BORDER AND ALONG THE SPINE OF THE DIVIDE. AREA
MOUNTAIN PASSES AND HIGH VALLEYS SHOULD ANTICIPATE DEGRADING
TRAVEL CONDITIONS TONIGHT THROUGH THE ENTIRE DAY ON WEDNESDAY. AT
THE SAME TIME, BACKCOUNTRY CONDITIONS WILL DETERIORATE QUICKLY,
DUE TO STRONG RIDGETOP WINDS (GUSTING TO 40-50 MPH) ALONG WITH
MODERATE TO HEAVY SNOW.
BY WEDNESDAY MORNING, VALLEYS ACROSS NORTH CENTRAL IDAHO AND
WESTERN MONTANA WILL BEGIN TO SEE SOME SNOWFALL, WHICH MAY MIX AT
TIMES WITH RAIN ALONG AND SOUTH OF THE I-90 CORRIDOR THROUGH THE
AFTERNOON HOURS. BY WEDNESDAY EVENING, THE COLD FRONT WILL CROSS
THE REGION, DRIVING SNOW LEVELS BACK DOWN TO VALLEY FLOORS AND
CHANGING PRECIP BACK OVER TO SNOW. DEPENDING ON HOW QUICK THIS
TRANSITION OCCURS WILL DETERMINE JUST HOW MESSY WEDNESDAY
AFTERNOON'S COMMUTE COULD GET (PARTICULARLY FOR LOCATIONS SUCH AS
THE MISSOULA/BITTERROOT VALLEYS, WHERE THE RAIN-TO-SNOW TRANSITION
ZONE WILL BE MOST NOTABLE).
WEDNESDAY NIGHT THROUGH THURSDAY: LINGERING SNOW IN THE MOUNTAINS
WILL CONTINUE, WHILE VALLEY SNOWFALL GRADUALLY TAPERS OFF THROUGH
THURSDAY MORNING. WHEN IT'S ALL SAID AND DONE, A STORM TOTAL
SNOWFALL AMOUNT ABOVE 4500 FEET WILL RANGE SOMEWHERE BETWEEN 10
TO 14 INCHES OF NEW SNOW.
THE EXTENDED RANGE OF THE FORECAST (FRIDAY THROUGH NEXT TUESDAY)
WILL BE LARGELY DOMINATED BY THE PRESENCE OF TWO VERY STRONG
WEATHER FEATURES SPREAD ACROSS NORTH AMERICA: AN AMPLIFIED HIGH
PRESSURE RIDGE ALONG THE WEST COAST, AND AN ANOMALOUSLY DEEP
TROUGH OF LOW PRESSURE EXTENDING FROM THE HUDSON BAY IN CANADA TO
THE GULF OF MEXICO. THE RESULTANT NORTHWEST FLOW ALOFT IS OFT RIPE
WITH WEAK WEATHER FEATURES THAT ARE VERY CHALLENGING FOR LONG
RANGE MODELS TO ACCURATELY DECIPHER. THE FIRST FEATURE APPEARS TO
QUICKLY PASS OVER THE NORTHERN ROCKIES FRIDAY, SPREADING LIGHT
SNOW ABOUT THE AREA. THE FLOW APPEARS TO SETTLE SOME FOR THE
WEEKEND, THOUGH THERE COULD STILL BE ADDITIONAL WEAK WEATHER
SYSTEMS PASSING THROUGH THE FLOW THAT MODELS ARE NOT DEPICTING AT
THIS TIME.
A MORE ROBUST LOW PRESSURE TROUGH APPEARS TO ACCOMPANY A POLAR
COLD FRONT AS IT PUSHES SOUTH OUT OF CANADA AND ACROSS THE PACIFIC
NORTHWEST AND NORTHERN ROCKIES EARLY NEXT WEEK. WHILE THIS MAY NOT
BE A FULL BLOWN 'ARCTIC' EVENT, THE AIR MASS EXCHANGE
ACCOMPANYING THE COLD FRONT COULD BE RATHER STARK. AND YES, A
PERIOD OF ADDITIONAL SNOWFALL SEEMS POSSIBLE AS WELL. THEREAFTER,
NORTHWEST FLOW ALONG WITH LOW FORECAST CONFIDENCE RESUME AND
PERSIST THROUGH AT LEAST MID WEEK.
AVIATION
CLOUDS WILL BE STEADILY INCREASING THROUGHOUT THE DAY
ACROSS THE REGION WHICH WILL HELP LIFT ANY FOG THAT HAS FORMED
EARLIER THIS MORNING. OTHERWISE FEW ADDITIONAL AFFECTS WILL BE
FELT BY THOSE WITH AVIATION INTERESTS THROUGHOUT THE AREA TODAY
AND THIS EVENING. LIGHT SNOW WILL BEGIN TO FALL AT KGPI AFTER
23/0800Z WITH THE POSSIBILITY OF LOWERED VISIBILITY AND CEILINGS
HEIGHTS CONTINUING INTO WEDNESDAY MORNING. WIDESPREAD TERRAIN
OBSCURATION WILL BE COMMON BY WEDNESDAY MORNING AS WELL.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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