Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 280955

Area Forecast Discussion
National Weather Service Missoula MT
355 AM MDT THU MAY 28 2015


The Bitterroot Valley and a few valleys of northwest Montana and
central Idaho could see patchy fog again this morning due to
recent rains. Any fog that does form should dissipate by mid-

Today will feature another round of showers and thunderstorms
popping up this afternoon in response to a weak upper-level low
passing by to our southeast. As was the case Wednesday, winds
aloft will be rather weak, and thus storms will be moving slowly.
This means the main threat would be heavy rain and associated
impacts with the stronger cells. Flash flooding in flood-prone
areas is not out of the question again, as precipitable water
looks to be similar to yesterday. The only difference is slightly
less instability today for most locations. Forecast models suggest
the best chance of storms will be over southwest Montana today,
and wind profiles indicate storms will generally be moving north
to south. Meanwhile, cooler air will move down from Alberta along
the east side of the Continental Divide this afternoon in the wake
of the upper low exiting the region. This will set up a weak back-
door cool front later today, bringing some breezy northeast winds
to the Flathead Valley and Glacier Park.

For Friday and into the weekend, a weak ridge of high pressure
will build over the Northern Rockies. A few showers and
thunderstorms will again pop up over the higher terrain, but fewer
storms are expected than we`ve seen the last few days. Light
overnight showers are possible both Friday and Saturday nights as
weak impulses move through the ridge. Meanwhile, the biggest
effect of the ridge will be warming temperatures. The urban Hwy 93
corridor of western Montana could top 80 degrees Sunday, which
would be the first time this year for many locations. The
Clearwater Valley of central Idaho could even approach 90.

Things change quickly by Monday as a vigorous upper-level low
moves into the Pacific NW and spins an upper-level trough and area
of enhanced moisture into the Northern Rockies. This southwest
flow scenario is historically favorable for stronger thunderstorms
across our area. If this pattern holds true, more widespread
storms capable of hail, heavy rain, and gusty winds would be

Cooler temperatures and generally showery conditions are expected
for the first half of next week as models indicate the Northern
Rockies will continue to be influenced by a series of low
pressure systems over the Pacific NW.


.AVIATION...Cloud cover remains through much of western Montana
and eastern Idaho this morning as a low exits the region. There
are also a few showers that will obscure terrain mainly from KSMN
to KBTM this morning. Simulated satellite loops show this
morning`s cloud cover to quickly transition into cumulus buildups
beginning around 28/1900z. These showers are first expected over
the terrain before slowly moving over valley locations during the
afternoon. There will again be enough instability this afternoon
for thunderstorm development with greatest storm chances before
29/0300z. Showers and thunderstorms will become more isolated
through the evening. Easterly winds are also forecast to develop
during the evening with cloud cover likely along the divide
through Friday morning.



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