766
FXUS65 KMSO 162026
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
226 PM MDT Sun Jun 16 2024

...Winter Storm to make backcountry travel hazardous tonight
through Tuesday night...

.DISCUSSION...Many of the watches have been upgraded to winter
storm warnings for the incoming weather system. Snow levels and
where the heaviest wrap-around precipitation will be are always a
struggle to predict in these scenarios. We looked at upstream
weather balloon soundings at Quillayute and Spokane, Washington
to help us understand how cold the incoming trough is compared to
climatology. The 9600 feet(700 millibars) temperature recorded in
the Quillayute (UIL) sounding was -9.9 degrees Celsius or 14
degrees Fahrenheit. This makes it the 2nd coldest temperature
(unofficially for the day) at this level...-10 degrees Celsius was
recorded on June 16, 1981. The freezing level was at 4458 feet.
Of course this trough will moderate a little bit in 24 hours as it
swings eastward. Under the heavier precipitation band with the
700mb low, snow levels could be driven down as low as 3200 feet
come Monday morning. Models continue to have a considerable spread
on where this could occur. Thinking back to the May 23 snow
event, there were locations at 4000 feet that saw snow and others
that only saw a mixture of rain and snow with no accumulation.
This could be a similar experience for folks on Monday.

Nonetheless, the impacts remain the same: backcountry travel will
be hazardous from north-central Idaho into western Montana. If you
are going to travel in these locations, make sure you have
emergency gear including a saw, extra food, clothes and water with
you. The locations that experience heavy snow could see some
branches broken and power outages.

Models have trended a little bit more robust with another
shortwave trough digging south out of Canada Tuesday morning. This
will keep the snow showers going across northwest Montana,
particularly in the Glacier Park region.

Wednesday morning could end up being quite cold in some valley
locations depending on cloud cover. Sensitive plants may need to
be covered.

Model ensembles agree on a warming trend for the rest of the week
with periods of afternoon showers.

&&

.AVIATION...Radar projections show showers increasing in coverage
this evening and overnight, as a low pressure system in
Washington circulates and moves into Idaho and western Montana.
Generally, precipitation in the form of rain is expected below
around 4000-5000 feet, with snow expected above 5000 feet late
Sunday into Monday. However, accumulations down to many valley
floors is possible under heavier precipitation, centered mainly in
west- central Montana. Winter storm warnings and advisories are
in effect for this very late season winter storm.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning from midnight tonight to 6 AM MDT Tuesday
     for Bitterroot/Sapphire Mountains...Butte/Blackfoot Region.

     Winter Weather Advisory from 6 AM Monday to 9 AM MDT Tuesday for
     West Glacier Region.

     Winter Weather Advisory from 3 AM to 11 AM MDT Monday for
     Missoula/Bitterroot Valleys.

     Winter Storm Warning from 3 AM Monday to 6 AM MDT Tuesday for
     Potomac/Seeley Lake Region.

ID...Winter Storm Warning from 11 PM this evening to 5 AM PDT Tuesday
     for Southern Clearwater Mountains.

     Winter Weather Advisory from midnight tonight to 2 PM MDT Monday
     for Eastern Lemhi County...Western Lemhi County.

&&

$$