textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Hot, dry, and smoky conditions continue through this week.

- Even hotter, drier, and windy conditions to end next week.

- Potential cool down to near average temperatures next weekend, though it remains dry.

A ridge over the western U.S. is leaving western Montana and central Idaho hot and dry. The ridge is being sustained by the Southwest Monsoon pattern that is currently going strong. However, the ridge axis, or its center, is located in central and eastern Montana, and that is steering any of the monsoon moisture east of our region. As a result, very dry air from the northeast Pacific Ocean region is being pulled in and then heated by the subsidence under the ridge. This will continue for the rest of the week. The exception to the dryness is the southern portions of Lemhi County, ID and much of southwest Montana where we expect thunderstorms today. But thunderstorms will be farther east the rest of the weekend and early next week. Overall, temperatures will remain about 10 degrees above average for this time of year through Wednesday or Thursday.

The air to the west is even drier, and it is helping to fuel the large wildfires in Oregon. There are also fires in Washington and British Columbia, but the direction of the flow means that most of the smoke in our area is coming from Oregon, and we expect the smoke to continue through this week at least.

The ridge builds back up towards the end of the week, just as a trough tries to push into the Pacific Northwest by Friday. This sets up a classic break down of the ridge pattern, which means hot, dry, and windy conditions for Friday and Saturday. This is a major concern for fire weather, especially after a week of hot, dry conditions drying the landscape.

Once the break down of the ridge finishes, the region will cool down to near average temperatures for this time of year over next weekend or into the following week. Looking at long term ensembles, the vast majority of the members support this transition, but there is a lot of variability in the timing. Some members have the cool down coming Saturday while others postpone it until as late as Monday. Either way, models aren't showing much moisture coming with the front, so it will remain dry and breezy through the weekend.

AVIATION

With a strong ridge over the region, the main aviation impacts will be from wildfire smoke originating in Oregon. Impacts from the smoke have been minimal at area terminals, with visibility getting as low as 5SM in the early morning hours, but generally improving through the day. With the ridge being stationary, we expect this pattern to continue through most of the coming week. The main exception to that pattern today is southwest Montana, which is getting some moisture from the Southwest Monsoon. This will mainly affect terminal KBTM this afternoon and evening with some thunderstorms.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Red Flag Warning until 9 PM MDT this evening for East Beaverhead.

ID...None.