textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Warming trend through next week.

- Strong winds gusting 40 to 50 mph on Tuesday across much of western Montana and north-central Idaho.

- 65% chance for winds briefly exceeding 50 mph in the Pinesdale area of the western Bitterroot Valley, 80% chance in Anaconda later Tuesday. Isolated tree damage possible.

- Considerable heat risk in the lower valleys of north-central Idaho as highs could reach upper 90s.

Tuesday will be unseasonably warm as strong afternoon mixing will help push valley temperatures into the 80s, and even 90s in the lower valleys of north-central Idaho and in the Salmon region. Highs could be in the upper 90s in the Salmon River valley south of Grangeville, throughout the Hells Canyon region, and towards Orofino.

Along with the heat, winds will begin developing by late morning and ramp up through the afternoon, potentially peaking by early evening. This will bring choppy lakes, which could be hazardous for small craft. High profile vehicles such as semis and RVs could be negatively impacted by strong crosswinds. Damage to trees and branches is possible along with localized power outages. Across southwest Montana, elevated fire weather concerns will exist as it will be hot, dry and windy. Winds could be sustained near 20 mph and gusts 30 to 40 mph across western Montana and in the higher terrain of Idaho.

Attention then turns to how conditions will evolve Tuesday evening as a weak and dry cold front moves north to south across the area. The pressure rises after 6 PM MDT will generally be several millibars...which is more like a broad pressure change rather than a sharp, punchy front. The main challenge is deciding how much of that evening wind profile actually reaches the ground. Cool air moving in aloft will strengthen the mid-level winds to around 58 MPH across west-central Montana. While these winds crossing the mountains will generate elevated mountain waves, high-resolution models suggest the strongest downward parts of the waves may miss the valley floors. Without showers or virga to help drag that momentum down, pulling the stronger winds through a developing evening cooling/stable layer will be more difficult. Even so, the threat cannot be entirely ruled out; the NBM shows 25 to 45% probability for localized winds briefly exceeding 50 mph along the west half of the Bitterroot Valley, up to 65% chance in the Pinesdale area.

There is a chance for showers and a few thunderstorms to pop off in the Glacier National Park, specifically over the Divide Tuesday evening. Impacts would be isolated lightning, gusty winds and small hail.

Wednesday will run 5 to 10 degrees cooler, which knocks temperatures briefly back to near seasonal normals. The exiting disturbance will likely bring showers and thunderstorms to northwest Montana, especially along the Continental Divide. However most other locations will remain dry.

A strengthening of the ridge looks likely again for Thursday and Friday, allowing temperatures to warm to similar levels as Tuesday, if not even slightly warmer. Another disturbance late Friday into Saturday again has the potential to bring wind and showers to the region.

AVIATION

VFR conditions will prevail today under high pressure, with localized terminal winds remaining under 15 knots. A strong northwesterly jet arrives Tuesday, bringing widespread surface gusts of 30 to 45 knots to western Montana terminals, with localized gusts near 50 knots possible downwind of the terrain(i.e. Bitterroot Mountains and mountains along the Continental Divide). Expect mountain wave activity and moderate turbulence aloft to peak between 6 PM MDT through 10 PM MDT Tuesday evening following a mostly dry frontal passage.

MSO WATCHES/WARNINGS/ADVISORIES

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