textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Warming trend through the rest of the week.

- Wildfire smoke will continue to impact the region until further notice.

- Ridge of high pressure flattens heading into the weekend. Near- critical to critical fire weather expected due to hot, dry and breezy conditions.

A ridge of high pressure will continue to build over the western United States, maintaining warm, dry, and stable conditions across western Montana and north central Idaho. Temperatures will warm significantly by Friday and Saturday, with lower elevations climbing back into the 90s and localized areas exceeding 100 degrees. As the upper ridge begins to flatten and transition into a more zonal flow this weekend, afternoon surface winds will increase. The combination of high temperatures, low relative humidity, breezy afternoon winds, and critically low fuel moisture will maintain near-critical fire weather conditions, likely peaking in intensity from Friday into Saturday.

Wildfire smoke will continue to be a forecast challenge across the region in terms of how much air quality is degraded. Strong radiational cooling under cloud-free, albeit smoky, skies will promote the development of sharp nocturnal valley inversions each morning. These inversions will trap particulate matter near the surface, degrading air quality and visibility during the morning hours. Afternoon diurnal heating will promote boundary layer mixing, which will temporarily aid in dispersing near-surface smoke. However, this increased ventilation will also invigorate regional wildfire activity, potentially generating thicker smoke plumes aloft. Current high-resolution smoke modeling indicates near-surface smoke concentrations will peak early this afternoon before modest improvement occurs with peak heating by early evening.

A subtle increase in mid-level moisture tracking along the periphery of the upper ridge may introduce a slight chance for high-based convection from Friday through the weekend, particularly across southwest Montana. The anomalously dry sub-cloud layer will pose a significant risk for localized, erratic convective wind gusts of 40 to 55 mph, alongside the threat of new lightning ignitions.

Heading into next week, forecast confidence remains low regarding a gradual increase in atmospheric moisture. A substantial synoptic pattern shift, such as the arrival of a deep Pacific Northwest upper-level trough, will ultimately be required to significantly diminish the prevailing fire weather threat and alleviate the persistent smoke. Current model runs show a 20 to 30 percent chance of this occurring by mid to late next week.

AVIATION

Widespread wildfire smoke will remain the primary aviation hazard through the next 24 hours, causing localized visibility reductions. Strong radiational cooling and sharp nocturnal inversions will trap particulate matter within valley locations, leading to periods of MVFR to localized IFR surface visibility reductions this morning. Afternoon diurnal heating will promote boundary layer mixing and modest improvements to surface visibility; however, this increased ventilation will concurrently invigorate regional wildfire activity, generating thicker smoke plumes aloft. Furthermore, high density altitude will be a prominent concern as afternoon temperatures climb into the 90s and localized 100s. Winds will generally be light and terrain driven.

MSO WATCHES/WARNINGS/ADVISORIES

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