textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Dry conditions with abnormally hot temperatures peaks today with elevated dry thunderstorms possible in the afternoon through the overnight.

- Thunderstorms Saturday pose marginal risks for severe-strength winds across the region and excessive rainfall in SW Montana and NC Idaho.

- Elevated to near-critical fire weather on Sunday due to gusty west winds accompanied by a very dry airmass.

High pressure remains in control over the Northern Rockies allowing for intense daytime heat that will peak this afternoon across the region. A rapidly growing wildfire near Happys Inn is pushing a plume of smoke to the east and northeast which may create reductions in visibility and air quality through the day today especially in the Flathead Valley and Glacier National Park.

Elevated monsoonal moisture will creep into Lemhi County and southwest Montana later this afternoon triggering high-based showers and dry thunderstorms capable of erratic convective outflow wind gusts of 30 to 45 mph. This convection pushes northward overnight into Saturday morning bringing nocturnal dry lightning and outflow risks along with it into the rest of western Montana.

An upper-level trough is still on track to lift out of the Pacific Northwest and phase with increasing monsoonal moisture on Saturday. Widespread shower and thunderstorm activity will increase through the afternoon and evening hours across the region. The Storm Prediction Center has place most of western Montana and north-central Idaho under a marginal risk for severe thunderstorms with damaging wind gusts being the primary threat. Where PWATS are forecast to near and exceed 1.0 inches in southwest Montana and Lemhi County on Saturday, a marginal threat for excessive rainfall, due to intense precipitation rates, also exists. Normally vulnerable spots such as burn scars, urban areas, and within steep terrain bear increased attention for flash flooding.

A cold front crosses through, from the west, Saturday evening into Sunday subduing convection from west to east and lowering daytime high temperatures by 10-15 degrees; closer to seasonal normals. However, the post-frontal environment will also bring deep mixing, strong westerly winds, and a very dry airmass creating elevated to near-critical fire weather conditions especially considering the preceding risk of new lightning starts and holdovers from Friday and Saturday's convection.

AVIATION

High pressure will maintain hot conditions and elevated density altitudes across the regional airspace today. A newfound fire near Happy's Inn is producing a significant plume of smoke that may impact visibilities to points east and northeast of the fire including KGPI. Elevated convection developing around and after 21/2000Z near KSMN and KBTM will spread northward into the evening and overnight bringing the risks of erratic outflow wind gusts of 25-40 knots, inducing low-level turbulence, and LLWS near these high-based storm cores. Widespread shower and thunderstorm activity on Saturday poses threats for strong to severe wind gusts, hail, and temporary MVFR/IFR weather conditions across the region particularly during the afternoon hours.

MSO WATCHES/WARNINGS/ADVISORIES

MT...None. ID...Heat Advisory from 11 AM this morning to 8 PM PDT this evening for Lower Hells Canyon/Salmon River Region... Orofino/Grangeville Region.