Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 180908

Area Forecast Discussion
National Weather Service Missoula MT
308 AM MDT Wed May 18 2022

...Gusty winds will develop today...

...Impactful snow accumulations in the Glacier National Park
Region and Marias Pass Thursday-Friday morning...

.DISCUSSION...A fairly nice start to the day is expected this
morning with mainly high cloud cover and quickly rising
temperatures. But, a well defined cold front is showing up on
satellite loops which will quickly move into the Pacific Northwest
today. The high temperature reading will be reached early in the
day with NBM temperature traces showing dropping temperatures in
most places just after noon-time. Winds will increase through the
morning and become gusty this afternoon. There is around a 90
percent probability of widespread wind gusts greater than 25 mph,
and Kalispell through Missoula and over to Butte have greater
than a 50 percent probability for gusts over 39 mph by midnight.
Flathead Lake is expected to have very choppy conditions today,
with a Lake Wind Advisory in effect from 11 am-9 pm.

Widespread showers are also expected in the warm frontal
environment late morning through early afternoon, followed by
briefly intense banded showers behind the cold front.

Snow levels will quickly lower this evening and tonight behind
the cold front, and the wind and moisture profile tonight are very
favorable for banded showers. By noon Thursday there are high
probabilities for measurable snow or more (90 percent probability
of > 1 inch) above 3000 feet in Idaho and Clearwater counties,
which may impact travel over Lolo Pass and Lost Trail Pass.
Valleys, such as the Missoula Valley also have around a 60 percent
probability of measurable snow by midnight Thursday night.

The main story for snow is in the Glacier Region as a low
pressure center slides down the east side of the Divide on
Thursday. The probability for greater than 2 inches above 4500
feet including Marias Pass is greater than 90 percent, so
confidence is high. The probability greater than 4 inches remains
high and ranges between 80 and 85 percent.

Thursday will also be a windy day with over a 60 percent
probability of greater than 47 mph winds in the
Mission/Missoula/Bitterroot valleys and Deer Lodge through Butte.

The Butte/Blackfoot Region is starting to get into a more
favorable snow pattern Thursday evening through Friday morning
with around an 80 percent probability of up to 1 inch, but around
a 65 percent probability of over 2 inches at MacDonald Pass by
Friday afternoon.

Cloud cover and wind on Saturday will keep most places from
getting exceptionally cold but the probability is high (90 percent
or greater) for below freezing temperatures along the Divide
Saturday morning.


.AVIATION...High level cloud cover is increasing across the
Northern Rockies this morning as a low pressure system moves
onshore in the Pacific Northwest. South-southwest winds will
increase after 18/1600z, with frequent gusts of 20-30 knots, as a
pacific cold approaches into eastern Washington. Widespread
showers will develop in the warm sector ahead of the front across
north-central Idaho and northwest Montana from 18/1800z to
18/2100z and will shift across west-central Montana thereafter.
The cold front will sweep across the area after 19/0000z.
Convective showers will develop along and behind the front,
leading to temporary visibility reductions.


MT...Lake Wind Advisory from 11 AM this morning to 9 PM MDT this
     evening for Flathead Lake in the Flathead/Mission Valleys.


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