936 
FXUS65 KMSO 232133
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
233 PM MST Sat Feb 23 2019

...PROLONGED SNOW EVENT FOR CENTRAL IDAHO AND MOST OF WESTERN
MONTANA...

.DISCUSSION...In northwest Montana this morning, an arctic surged
across the Continental Divide, and is still causing snow from
Marias Pass to Kalispell. In addition, northeast winds are still 
gusting over 30 mph out of Badrock Canyon. Tonight, as the cold 
air spills into the area, wind chills will be a concern.

Elsewhere in the Northern Rockies today, snow showers this 
afternoon will taper off this evening just in time for a warm 
front to start moving north into the region. Several advisories
have been issued from central Idaho through west central Montana
for this event. For most of central Idaho, this is the beginning
of a prolonged snow event. Overall, snow accumulations will be 
high for the event, but snow rates for many areas will remain low 
enough that elevating the advisories to warnings is not warranted
at this time.

The exception is the northwest corner of Lemhi County in Idaho. A
winter storm warning been issued, as this area will receive 8 to 
12 inches of snow in the next 24 hours. Combined with wind, some 
exposed areas like Williams Creek Pass may become impassable at 
times.

Widespread snowfall will continue through the day Monday, 
becoming intense at times across the Clearwater mountains and 
eastward into the Bitterroot valley by Monday evening. Lolo Pass,
Lost Trail Pass, and locations from Lolo, MT south through Darby
may see a period of heavy snow during the evening time frame,
lasting into the overnight period. If this area of heavier snow
develops, roughly 6 to 10 inches of snow could result. Confidence
is moderate at this time, but forecast models have been 
consistent in showing a period of enhancement during the evening 
commute in the Bitterroot valley. 

During the same time, gusty easterly winds will be howling 
through Hellgate Canyon and East Missoula, which will have a
negative effect on snowfall accumulations, limiting snowfall 
totals. As a result, snowfall amounts in and around the Missoula 
valley are expected to be less than those forecast for the 
Bitterroot valley: ranging from about 3 to 6 inches. 

Conditions in the backcountry/high elevation terrain around west
central Montana will be downright dangerous, as winds and heavy 
snow will combine to create hazardous conditions, both over 
mountain passes and in the general backcountry. 

Northwest Montana during this time will see very light snowfall,
if any. This may change, however, by Tuesday as the focus of
precipitation may take a northward track. Confidence is low in
this occurring, but the potential is there for additional snowfall
Tuesday morning through Tuesday evening. 

Conditions remain unsettled and moist through the rest of the
week for the Northern Rockies.

&&

.AVIATION...A prolonged winter storm system will affect most 
regional terminals for the next several days. An arctic front from
this morning is causing snow, blowing snow, and strong northeast 
winds at KGPI. As the snow tapers off tonight, wind chills will become
more of a concern. KSMN, KBTM, and KMSO will have restrictions at
times due to snow showers giving way to more steady snow tonight 
and tomorrow.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch from Monday morning through Tuesday morning 
     Bitterroot/Sapphire Mountains.

     Winter Weather Advisory until noon MST Sunday Flathead/Mission 
     Valleys...West Glacier Region.

     Winter Weather Advisory from 6 AM Sunday to 11 AM MST Monday 
     Bitterroot/Sapphire Mountains.

     Winter Weather Advisory from 6 AM Sunday to 6 AM MST Monday 
     Butte/Blackfoot Region.

     Winter Storm Watch from Monday morning through Tuesday morning 
     Missoula/Bitterroot Valleys.

ID...Winter Weather Advisory from 5 AM Sunday to 10 AM PST Tuesday 
     Lower Hells Canyon/Salmon River Region...
     Orofino/Grangeville Region.

     Winter Storm Watch from Monday morning through Tuesday morning 
     Southern Clearwater Mountains.

     Winter Weather Advisory from 6 PM this evening to 6 AM MST 
     Sunday Western Lemhi County.

     Winter Storm Warning from 6 AM Sunday to 6 AM MST Monday Western 
     Lemhi County.

     Winter Weather Advisory from 6 PM this evening to 6 AM MST 
     Monday Eastern Lemhi County.

     Winter Weather Advisory from 5 AM Sunday to 10 AM PST Monday 
     Southern Clearwater Mountains.

&&

$$