334
FXUS65 KMSO 042020
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
220 PM MDT Sat May 4 2024

.DISCUSSION...A closed low pressure circulation spinning off the
coast of the California-Oregon border is quite prominent on
satellite imagery this afternoon. This feature, along with an
amplifying ridge east of the Continental Divide, will be the main
players in the weather over the next couple of days. For this
afternoon and well into tonight, higher pressure east of the
Divide will power easterly winds gusting to about 20 mph across
much of western Montana and Lemhi County, especially along the
Divide and higher terrain east of about Highway 93.

As the Pacific low makes its way inland across Oregon, it will
push Pacific moisture into the Northern Rockies from the
southwest. Rain will start over north-central Idaho this afternoon
or evening and spread northwest overnight tonight and on Sunday.
Cooler temperatures associated with this system will bring snow
levels down to about 5000 feet by Monday morning. Motorists should
expect snow over Homestake, Lost Trail, and Lolo Passes as well
as Gilmore Summit in Idaho. Chances for 2 inches of snow by Monday
morning about about 50 to 80%. Unsettled weather will continue on
Tuesday, mostly in the form of clouds, rain, and gusty west
winds. As this system moves east of the Continental Divide, it
will send wraparound moisture into the Glacier Park region of
northwest Montana for Wednesday morning. Impacts on Wednesday
morning should be limited to high terrain of Glacier Park. One
notable exception will be Marias Pass, where there is a 60- 70%
chance of about 4 inches of snow on Wednesday morning.

The bulk of the low pressure system will move off to the east
while a portion of energy drifts back to the Great Basin region
during the latter part of the work week. This pattern shift will
leave the Northern Rockies in a weak northerly to easterly upper
level flow Wednesday through Friday. Temperatures will gradually
warm, but still remain below normal. Shower activity is expected
to decrease in coverage and intensity each day.

Model ensemble solutions are leaning towards a positively tilted
ridge over the northwestern U.S. by next weekend. This scenario
would mean a warming and drying trend for the weekend.


&&

.AVIATION...An approaching trough from the west and high pressure
east of the Continental Divide will result in gusty easterly winds
to about 20-25 knots this afternoon and overnight tonight. Expect
increasing clouds and decreasing ceilings as the trough
approaches. Rain showers will move from southwest to northeast
tonight and become widespread on Sunday.






&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$