Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 212038

Area Forecast Discussion
National Weather Service Missoula MT
238 PM MDT Sat May 21 2022

.DISCUSSION...Cool and showery conditions will persist for the
Northern Rockies this weekend as a low pressure system remains in
place. The circulation associated with the low is currently
centered over the Idaho/Washington/Oregon border and it`s causing
showers and thunderstorms to develop over north central Idaho. The
circulation will slowly move to the south and east this afternoon
and overnight causing the shower activity to move into west
central Montana. The majority of the activity will stay south of
the I-90 corridor. Storms will be capable of producing moderate to
heavy rain, driving snow levels down to around 4000 feet and
potentially even small hail.

The shower activity will diminish during the evening hours, but a
few light showers could linger across southern Idaho county into
Lemhi county tonight. These showers might put down a light coating
of snow, especially over higher terrain.

Sunday will be slightly warmer compared to today, but still be
slightly below seasonal readings. The low pressure circulation
appears to be over Lemhi county and southwest Montana by Sunday
afternoon, this will be the main area of focus for convection
development. Once again the main threat from the storms will be
brief heavy rain, lowered snow levels and small hail.

On Monday a weak disturbance will move through the Northern
Rockies from British Columbia. This disturbance will cause
widespread shower activity with the heaviest precipitation being
along the Montana/Idaho border.

The models continue to indicate a ridge of high pressure will
begin to move over the Northern Rockies on Tuesday and become the
dominant feature for the middle part of the work week. This ridge
will cause temperatures to warm to seasonal readings by Wednesday
and be around 10 degrees above normal for Thursday. The current
model solutions are starting to indicate that the ridge will not
be as dry as previously forecasted, so the potential of
afternoon/evening convection is increasing.

This ridge of high pressure will be short lived as a fairly strong
cold front is expected by Friday with the Northern Rockies
returning to a cool and showery pattern for the holiday weekend.


.AVIATION...A low pressure circulation combined with daytime
heating has aided in the development of widespread showers and
isolated thunderstorms in north central Idaho this afternoon.
These showers will continue to develop to the east into southwest
and west central Montana through this afternoon, generally along
and south of Interstate 90. The main threats will be a few
lightning strikes, brief heavy rain, and possibly some small hail.
Airfields KSMN and KBTM will be most impacted, though KMSO also
could see a brief period of showers this afternoon. Northwest
Montana, including KGPI will generally remain dry. Locally lowered
visibility and obscured terrain can be expected in the vicinity of
showers. A breezy east to northeast wind will continue into
tonight across western Montana, though overall it should weaken
from speeds seen this morning, generally 15kts or less.



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