Snow Squall Warning 19, NWS Missoula, MT

Area Forecast Discussion
National Weather Service Missoula MT
244 PM MST Sun Nov 27 2022

.DISCUSSION...Snow bands and snow squalls are moving from north to
south in western Montana and north-central Idaho. Low visibility
and quickly accumulating snowfall have been observed with squalls
today, and locations south of Highway 12 will have impacts from
periods of low visibility and high snow intensity into this
evening. Recent radar trends show snow bands developing behind the
main cold frontal band, so additional shower chances have been
added to the forecast. The front is projected to be in Lemhi
County late this evening where periods of heavy snow will linger
overnight. Banded showers are also projected to be numerous in
north-central Idaho with accumulations expected overnight and
through Monday.

The snow forecast for Monday forecast has been challenging with
model guidance in disagreement on the amount of available moisture
and on the timing of an arctic front approaching from the
northeast. Radar projections are starting to show more and more
shower development on Monday, so the chance for snow has been
increased areawide.

A cold start to the day on Tuesday is likely, with lows below
zero along the Continental Divide, and low single digits elsewhere
across western Montana. North-central Idaho will not be quite as
cold, but still in the low to mid teens. In terms of moisture, a
few isolated snow showers will be possible in the afternoon and
evening, but by and large, Tuesday will be the driest day of the
week.

Starting Wednesday and going through the rest of the week, a
series of weather disturbances will stream abundant Pacific
moisture over the Northern Rockies, bringing considerable amounts
of mountain snowfall. As for the valleys, there's increasing
chances (30-40%) that an arctic airmass will arrive around the
time a second surge of moisture moves in sometime Thursday and/or
Friday. The interaction of these two airmasses would produce
widespread moderate to heavy snowfall to most elevations of
western Montana and north-central Idaho. At this time, there is
still quite a bit of uncertainty in how far south the arctic air
makes it into western Montana, and the timing of the moisture.
However, heavy mountain and mountain pass snows can be expected,
and all elevations of northwest Montana may be cold enough to
where the arctic airmass isn't needed for significant snow
accumulations. Stay tuned to the forecast, as changes will likely
occur as we get into the first couple of days this coming week.

&&

.AVIATION...A strong cold front continues to impact north-central
Idaho and western Montana. The front has passed through northwest
Montana and snow showers are developing, which will cause brief
ceiling and visibility reductions. The main front will continue
progressing southeastward during the afternoon and evening, and
will continue to create snow squall conditions of heavy snow, low
visibility and gusty winds. By 28/0600z, the front is projected to
be in Lemhi County where periods of heavy snow will linger.
Northeasterly winds and additional snow showers are expected to
develop on Monday with an arctic airmass moving into the region.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...     Winter Weather Advisory until 3 PM MST this afternoon for
     Kootenai/Cabinet Region.

     Winter Weather Advisory until midnight MST tonight for West
     Glacier Region.

     Winter Weather Advisory until 3 PM MST this afternoon for
     Flathead/Mission Valleys.

     Winter Weather Advisory until midnight MST tonight for Lower
     Clark Fork Region.

     Winter Weather Advisory until midnight MST tonight for
     Bitterroot/Sapphire Mountains.

     Winter Weather Advisory until midnight MST tonight for
     Butte/Blackfoot Region.

     Winter Weather Advisory until midnight MST tonight for
     Potomac/Seeley Lake Region.

ID...Winter Storm Warning until 8 AM PST Monday for Northern
     Clearwater Mountains.

     Winter Storm Warning until 8 AM PST Monday for Southern
     Clearwater Mountains.

     Winter Weather Advisory until 10 PM PST Monday for
     Orofino/Grangeville Region.

     Winter Weather Advisory until 10 PM PST Monday for Lower Hells
     Canyon/Salmon River Region.

     Winter Weather Advisory until 9 AM MST Monday for Eastern Lemhi
     County...Western Lemhi County.

&&

Special Weather Statement
National Weather Service Missoula MT
141 PM MST Sun Nov 27 2022

MTZ004>006-043-272130-
Bitterroot/Sapphire Mountains MT-Missoula/Bitterroot Valleys MT-
Lower Clark Fork Region MT-Potomac/Seeley Lake Region MT-
141 PM MST Sun Nov 27 2022

...An intense snow shower will impact portions of south central
Missoula County through 230 PM MST...

At 140 PM MST, Doppler radar was tracking an intense snow shower over
Missoula, moving east at 25 mph.

HAZARD...Visibility one-half mile or less and winds in excess of 30
         mph.

SOURCE...Radar indicated.

IMPACT...Low visibility could result in dangerous driving
         conditions. Gusty winds could knock down tree limbs and
         blow around unsecured objects.

Locations impacted include...
Missoula, Lolo, Bonner-West Riverside, Wye, East Missoula,
Frenchtown, Evaro and Turah.

This includes the following highways...
 Interstate 90 near mile marker 81, and between mile markers 85 and
115.
 Highway 93 N between mile markers 0 and 8.
 Highway 93 S between mile markers 83 and 94.
 Highway 200 E between mile markers 0 and 5.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4702 11438 4707 11404 4683 11365 4676 11411
TIME...MOT...LOC 2040Z 285DEG 22KT 4690 11399

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...30 MPH

Special Weather Statement
National Weather Service Missoula MT
209 PM MST Sun Nov 27 2022

MTZ005>007-043-272200-
Bitterroot/Sapphire Mountains MT-Missoula/Bitterroot Valleys MT-
Butte/Blackfoot Region MT-Potomac/Seeley Lake Region MT-
209 PM MST Sun Nov 27 2022

...Intense snow showers will impact portions of southeastern
Missoula, northern Granite, north central Ravalli and central Powell
Counties through 300 PM MST...

At 208 PM MST, trained weather spotters reported intense snow showers
along a line extending from 7 miles northeast of Drummond to 7 miles
west of Victor. Movement was southeast at 20 mph.

HAZARD...Visibility one-quarter mile or less and winds in excess of
         30 mph.

SOURCE...Trained weather spotters.

IMPACT...Low visibility could result in dangerous driving
         conditions. Gusty winds could knock down tree limbs and
         blow around unsecured objects.

Locations impacted include...
Hamilton, Drummond, Stevensville, Victor, Woodside, Pinesdale,
Nimrod, Finn, New Chicago, Bearmouth, Quigley, Corvallis, Helmville,
Bell Crossing and Hall.

This includes the following highways...
 Interstate 90 between mile markers 130 and 158.
 Highway 93 S between mile markers 48 and 68.
 Highway 200 E between mile markers 58 and 61.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

These snow showers may intensify, so be certain to monitor local
radio stations and available television stations for additional
information and possible warnings from the National Weather Service.

&&

LAT...LON 4675 11263 4623 11425 4649 11434 4695 11286
      4689 11279 4683 11280 4683 11272
TIME...MOT...LOC 2108Z 293DEG 19KT 4676 11307 4646 11431

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...30 MPH