Snow Squall Warning 2, NWS Missoula, MT

Area Forecast Discussion
National Weather Service Missoula MT
217 PM MST Wed Jan 5 2022

...HEAVY SNOW THROUGH FRIDAY ACROSS WESTERN MONTANA AND CENTRAL
IDAHO...

.DISCUSSION...Light snow will continue across the region through
this evening. Then tonight, the atmospheric river arrives. Between
10 PM and midnight, depending on location, the snow rates will
start to increase quickly. The atmospheric river brings much
warmer air with it as well, which is the main challenge in the
forecast. As we are writing this discussion, cold air is draining
into the Missoula valley from the east. How much cold air will
make it in? How deep will the cold air be? Those will be the
determining factors for the forecast in Missoula and the
Bitterroot valley. The remainder of western Montana will be well
entrenched in the arctic air. This arctic is not anticipated to
move into north central Idaho.

The heaviest precipitation and snow are expected early tomorrow
morning which will cause a lot of trouble for the morning commute.
One inch per hour snow rates will affect much of the region, but
especially west central Montana along the I-90 Corridor. By 11 AM
we expect several inches of new snow in Missoula on top the new
snow we got today. Of course most of the region will be getting
heavy snow. The only exceptions are Butte and the portions of the
Camas Prairie in Idaho, however, even these locations will pick up
3-4 inches of new snow.

During the day Thursday the snow levels will rise, and this is
where the depth of the cold air becomes important. Hamilton and
Butte areas will be the first to break out of the cold air
sometime Thursday afternoon or evening. It will be very unlikely
for Missoula ,potentially Bonner to Ovando or Drummond, to break
out of the cold air. As a result somewhere between Missoula and
Hamilton (including Missoula) or along the I-90 corridor will
probably see freezing rain. The best chance for freezing rain is
late Thursday.

The Camas Prairie in Idaho is an area that will likely see a few
hours freezing rain on Thursday as they break out of the cold air.
By Friday, most of the Camas Prairie should be in rain while the
mountains continue to snow.

The focus for the precipitation moves back to the north again on
Friday. The Idaho Panhandle and northwest Montana will see their
highest precipitation rates Thursday night and Friday morning.
Over a 2 day period including Thursday and Friday, much of
northwest Montana valleys west of Kalispell could see a foot or
more of snow. The mountains will see 2 to 3 feet of snow. Saturday
things taper off, but some increasing winds could cause
difficulty with blowing snow in northwest Montana.

Overall, this is a complicated system with a lot of changes
throughout, so please look at your local forecasts for more
details.

Sunday onward a ridge of high pressure builds in setting us up
for some drier, more stable weather next week.

&&

.AVIATION...The snow has transitioned over to more of banded
convection pattern. Most areas will only experience light snow
creating MVFR conditions, but under bands conditions can rapidly
change to LIFR. The precipitation will transition back over to
steady stratiform this evening and overnight. This stratiform
precipitation will steadily increase in intensity after midnight
tonight across all of western Montana with most locations
experiencing moderate to heavy snowfall rates by early Thursday
morning. KGPI has the least probability of being impacted by the
heaviest of snowfall rates. Snowlevels will be rising during the
afternoon hours with KSMN and KBTM potentially transitioning over
to rain. While KMSO could experience freezing rain by Thursday
afternoon.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory until 11 PM MST this evening
     Butte/Blackfoot Region.

     Winter Storm Warning from 11 PM this evening to 11 AM MST Friday
     Butte/Blackfoot Region.

     Winter Weather Advisory until 8 PM MST this evening
     Bitterroot/Sapphire Mountains.

     Winter Storm Warning from 8 PM this evening to 11 AM MST
     Saturday Bitterroot/Sapphire Mountains.

     Winter Weather Advisory until 11 PM MST this evening
     Missoula/Bitterroot Valleys.

     Winter Storm Warning from 11 PM this evening to 11 AM MST Friday
     Missoula/Bitterroot Valleys.

     Winter Weather Advisory until 8 PM MST this evening Lower Clark
     Fork Region.

     Winter Storm Warning from 8 PM this evening to 11 AM MST
     Saturday Lower Clark Fork Region.

     Winter Weather Advisory until 11 PM MST this evening
     Flathead/Mission Valleys.

     Winter Storm Warning from 11 PM this evening to 11 AM MST Friday
     Flathead/Mission Valleys.

     Winter Storm Warning from midnight tonight to 5 PM MST Saturday
     West Glacier Region.

     Winter Storm Warning from 11 PM this evening to 11 PM MST Friday
     Kootenai/Cabinet Region.

     Winter Weather Advisory until 11 PM MST this evening
     Potomac/Seeley Lake Region.

     Winter Storm Warning from 11 PM this evening to 11 AM MST Friday
     Potomac/Seeley Lake Region.

ID...Winter Weather Advisory until 8 PM MST Thursday Eastern Lemhi
     County...Western Lemhi County.

     Winter Weather Advisory until 7 PM PST this evening Northern
     Clearwater Mountains...Southern Clearwater Mountains.

     Winter Storm Warning from 7 PM this evening to 10 AM PST
     Saturday Northern Clearwater Mountains...Southern
     Clearwater Mountains.

     Winter Weather Advisory until 4 PM PST Thursday Lower Hells
     Canyon/Salmon River Region.

     Winter Weather Advisory until 7 PM PST this evening
     Orofino/Grangeville Region.

     Winter Storm Warning from 7 PM this evening to 4 PM PST Thursday
     Orofino/Grangeville Region.

&&

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
511 PM MST WED JAN 5 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0400 PM     SNOW             1 WSW THOMPSON FALLS    47.59N 115.36W
01/05/2022  M4.0 INCH        SANDERS            MT   CO-OP OBSERVER

            CO-OP OBSERVER STATION THOM8 0.8 W THOMPSON
            FALLS.

&&

JM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
512 PM MST WED JAN 5 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0900 AM     SNOW             5 NNE CORVALLIS         46.38N 114.06W
01/05/2022  M5.1 INCH        RAVALLI            MT   COCORAHS

            COCORAHS STATION MT-RV-15 VICTOR 5.4 SE.

&&

JM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
513 PM MST WED JAN 5 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0900 AM     SNOW             2 NW CLINTON            46.79N 113.74W
01/05/2022  M2.0 INCH        MISSOULA           MT   COCORAHS

            COCORAHS STATION MT-MS-22 1 NW CLINTON.

&&

JM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
514 PM MST WED JAN 5 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0900 AM     SNOW             4 ESE FLORENCE          46.61N 114.01W
01/05/2022  M1.9 INCH        RAVALLI            MT   COCORAHS

            COCORAHS STATION MT-RV-5 3 ESE FLORENCE.

&&

JM