textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Mild and fair weather continues this morning, followed by increasing clouds and chances for thunderstorms this afternoon.

- Showers and isolated thunderstorms continue through the weekend, bringing gusty winds and rain.

- Cooler temperatures and mountain snow arrive Monday.

Satellite imagery early this morning depicts a well-formed low pressure circulation off the coast of northern California and an elongated trough off the coast of northern British Columbia. Over the next few days, the northern low will move south, then inland, bringing a prolonged period of unsettled weather with it. Until then, most of the day today will remain mild with clear skies and light winds. Moisture starts to move into north-central Idaho and western Montana south of about I-90 this afternoon. Expect increasing clouds, showers, and chances for thunderstorms (about 10%) for southern Idaho, Lemhi, and Ravalli counties late this afternoon through the overnight hours. Because the lower atmosphere will initially be quite dry, evaporating rain from these initial showers could produce sudden, gusty winds at the surface.

The Pacific low moves inland on Saturday, dragging abundant moisture into the Northern Rockies. As daytime temperatures peak on Saturday afternoon, expect widespread showers and scattered thunderstorms to develop. There is a 10 to 20 percent chance of lightning, with the greatest potential over western Idaho and Clearwater counties. Gusty winds and brief heavy rain could accompany the stronger cells.

By Sunday and Monday, the core of the system moves overhead, bringing a noticeable cool-down to more seasonal temperatures. Expect widespread valley rain and high elevation snow as cooler air filters in.

Tuesday through Thursday: The active spring weather pattern is likely to continue through the middle of next week. We may see a brief break with fair weather, but another Pacific weather system is currently favored to bring additional chances for valley rain and mountain snow by Wednesday. Snow levels look to drop on Wednesday, so travel impacts may include several inches of snow on Lookout, Lolo, Lost Trail, and Marias passes.

AVIATION

VFR conditions will prevail this morning, with the exception of KHRF, where low stratus could hang around until after sunrise. High clouds will increase this afternoon from south to north. Shower activity will follow, expect about a 30 percent chance for showers at KSMN and KHRF by about 10/2200Z and lasting overnight. A dry lower atmosphere will be conducive to gusty, erratic winds accompanying any thunderstorm activity.

MSO WATCHES/WARNINGS/ADVISORIES

MT...None. ID...None.