textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Thunderstorms this afternoon and evening east of US-93 through 10pm MDT bringing risk of lightning and strong outflow gusts.

- Critical fire weather this weekend.

- Cooldown for Sunday and Monday with temperatures rebounding to near/above normal by Tuesday and Wednesday of next week.

Hot, dry, and smoky conditions remain entrenched today with high- based, inverted-V profile, dry thunderstorms developing this afternoon primarily east of US-93 and along the HWY 200 corridor. Rain totals will be minimal and isolated, primary hazards from convection today between 4pm and 10 pm MDT will be lightning (and any new fire starts that occur) and strong erratic outflow winds gusting 30 to 45 mph (low chance for an isolated 50+ mph). Friday will be mostly convection-free, hot, dry, and smoky serving as the calm (and continuing to pre-condition wildland fuels) before this weekend's weather event.

High confidence remains in a critical fire weather pattern this weekend as a dry Pacific trough pushes a cold front through the region. Pre-frontal heating peaks on Saturday with temperatures approaching 100 degrees in valleys south of I-90 and in southwest Montana. Widespread westerly winds ramp up Saturday afternoon, gusting 25 to 40 mph (with ridgetops approaching 50 mph) alongside relative humidities dropping to at least 10-15%. Current Fire Weather Watches remain active, with Red Flag decisions planned to be finalized on Friday's day shift. Post- frontal cold air advection drops temperatures 10 to 20 degrees for Sunday and Monday, though strong westerly breezes persist across the Northern Rockies on Sunday keeping SW Montana in critical fire weather conditions through Sunday evening.

Northwest flow dominates Monday and Tuesday, keeping highs below seasonal averages with cool overnight lows. Isolated mountain showers are possible but moisture will be severely limited. A thermal ridge begins to rebuild by midweek next week marking the return of above normal high temperatures.

AVIATION

Hot temperatures will keep density altitudes elevated across all regional terminals through Saturday (peaking near 9,000 ft at KBTM). Deep southwesterly flow continues to transport wildfire smoke across the region, degrading slant-range visibility and keeping surface visibilities near 6SM. High-based isolated dry thunderstorms develop 30/2000z through 31/04z along and mostly east of a straight-line from KHRF to KMSO. 8-12k ft AGL cloud bases will produce minimal surface rain nor prolonged visibility reductions, but strong erratic outflow gusts of 25-35 knots (isolated 45 knots) near KBTM, KSMN, and KHRF remain the main hazard.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Fire Weather Watch from Saturday afternoon through Saturday evening for Bitterroot...East Lolo...Flathead Reservation... Flathead/Glacier Park...Kootenai...West Lolo.

Fire Weather Watch from Saturday afternoon through Sunday evening for Deerlodge/West Beaverhead...East Beaverhead.

ID...Fire Weather Watch from Saturday morning through Saturday evening for Clearwater/Nez Perce...Palouse/Hells Canyon.