Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 312107

Area Forecast Discussion
National Weather Service Missoula MT
307 PM MDT Tue Mar 31 2020

.DISCUSSION...A closed system of low pressure over Alberta is the
centerpiece of a broad trough over much of the Pacific Northwest
today. This is creating unsettled weather throughout the Northern
Rockies. Moisture from the west is streaming up from the Pacific,
while a cold front associated with the Canadian low- pressure
center moves over the Continental Divide from the east later
tonight. Mix in a little instability and you have a nice recipe
for bands of convective precipitation. Radar and spotters are
already indicating lightning in the vicinity of Glacier Park
International and the Columbia Falls area this afternoon. The
ingredients are in place for more convective activity on
Wednesday, including bands of showers producing snow, graupel or
hail, gusty winds, and the occasional lightning strike.

Tonight into Wednesday morning a Canadian cold front will cross
the Continental Divide into northwest Montana. A more focused area
of precipitation is expected to develop ahead of this front, which
will also be accompanied by gusty northeast winds. Snow will be
possible for both mountain passes and valleys as colder air
filters into the region. The Flathead valley in particular could
see some challenging conditions by Wednesday morning as wet/slushy
roads this evening could freeze up, creating black ice. The
further west, as you move closer to the Idaho panhandle, the less
likely the colder air will settle in tonight. That leaves some
question marks for the valleys of far northwest Montana, where
road conditions could degrade due to snowfall and ice, however
this will be very dependent on timing and placement of showers.

On Friday, unstable westerly flow will set up into Saturday
leading to a scattering of showers, especially during the
afternoon and evening. It`s not uncommon for showers to be more
widespread than forecast models depict in northwest or west flow,
especially if a disturbance rotates through. Overall impacts
appear minimal unless showers persist into the overnight hours.

Later Saturday into Sunday morning, a weak low pressure system
may try to spin up over southern Idaho, but confidence is low. If
this were to occur then widespread, albeit light snow would
develop from Lemhi County into Southwest Montana.

Looking from Sunday through much of next week, a general trough
will remain over the western U.S. leading to cooler than normal
temperatures and showery weather at times. The most likely
"significant" impacts would be snow accumulations on passes during
the overnight hours as road temperatures decrease. If a stronger
disturbance can focus precipitation though, light snow would be
possible in the valleys. The overall details are far from clear
for next week as forecast models continue to struggle with the
changeable springtime weather patterns.


.AVIATION...Unstable atmospheric conditions have led to the
development of widespread showers across western Montana and
central Idaho this afternoon. A few lightning strikes are also not
out of the question. Precipitation will mainly fall as snow
and/or graupel due to the convective nature of showers. All
airfields will have potential brief periods of limited
ceiling/visibility due to snow and breezy southwest to westerly
winds through this afternoon. KBTM in particular is expected to
see a more focused area of precipitation, lowering ceilings and
visibility at times between 31/2100z and 31/2400z. Tonight, a
Canadian cold front will cross the Continental Divide, bringing
snow and breezy northeast winds into primarily northwest Montana.
KGPI will likely see winds increase from the north around 01/0600z
with gusts to 30 kts possible. This front will likely be
accompanied by snow, lowering visibility and ceiling until roughly
01/1200z. Widespread obscurations of the terrain should be
anticipated across all of western Montana and central Idaho into
Wednesday morning.


MT...Winter Weather Advisory until midnight MDT tonight
     Butte/Blackfoot Region.

     Winter Weather Advisory from 9 PM this evening to noon MDT
     Wednesday Flathead/Mission Valleys.

     Winter Weather Advisory until noon MDT Wednesday West Glacier

ID...Winter Weather Advisory until midnight MDT tonight Eastern Lemhi
     County...Western Lemhi County.


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