textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Strong to severe thunderstorms this afternoon and evening across north-central Idaho, tracking toward the Montana state line. Hazards include gusts up to 60 mph and up to 1-inch hail.

- Elevated fire weather (hot, dry, breezy) starting Friday and lasting into the weekend region-wide.

- Worsening wildfire smoke degrading air quality and reducing visibility.

The region remains on the western periphery of a large- scale upper-level ridge. Persistent synoptic descent and subsidence aloft will maintain, hot, dry, and smoky conditions with no widespread precipitation anticipated through the weekend.

Despite broad subsidence, localized thermodynamic forcing will help to trigger strong to severe convection today (1:00 PM - 10:00 PM). Effective shear (~40 kt), modest CAPE (~1,000 J/kg), and high DCAPE (~1,500 J/kg) will support organized discrete storms initiating near the Snake River canyon in north-central Idaho tracking northeastward to the ID/MT border. The strongest storms in this environment will be capable of producing damaging winds up to 60 mph and hail up to 1-inch in diameter. Climatologically high moisture availability (PWATS > 1 inch) will yield brief heavy downpours, but rapid storm movement will prevent concerns for flash flooding. There is a 10-20% chance that decaying storms reach the I-90 corridor late this evening which may bring a gusty outflow threat to the area.

Breezy southwesterly winds Friday through Sunday will combine with low humidity and hot temperatures to elevate fire weather concerns. Red Flag Warnings are not currently being issued due to live fuels and soil moisture remaining relatively high for this time of year and wind speeds only on the edge of what would be an immediate concern for fire weather products. Nonetheless, elevated fire weather conditions and increased active fire behavior is to remain expected on any active burns or new ignitions.

Deep SW flow will continually transport Washington and Oregon wildfire smoke into ID/MT, maintaining poor air quality and decreased visibilities across the region. No Heat Advisories are planned as of yet due to overnight temperature recovery and shading from smoke limiting absolute maximum temperatures during the peak of the afternoon hours.

AVIATION

Wildfire smoke (FU/HZ) remains the primary prevailing hazard, causing periods of MVFR visibilities through the next couple days especially noticeable near sunset, through the overnight and into mid-morning with some clearing each afternoon due to deep mixing. Ridgetop winds increase to about 30 knots through today out of the west and southwest with surface wind gusts as high as 30 knots possible region-wide during peak heating.

Strong to severe convection today mostly targets KGIC from 23/2200z to 24/0300z (isolated gusts up to 60 mph possible, hail up to 1 inch in diameter). Activity decays to the northeast near I-90 where prob30 groups remain for elevated winds at KHRF and KMSO.

Hot temperatures, especially Friday, will impact aircraft performance particularly at higher-elevation terminals like KBTM.

MSO WATCHES/WARNINGS/ADVISORIES

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