408 FXUS65 KMSO 021850 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 1250 PM MDT Wed Jul 2 2025 .DISCUSSION... KEY MESSAGES: - Strong to isolated severe thunderstorms today mainly across west central Montana, southwest Montana, and Lemhi County, Idaho - A trough Friday and Saturday will bring thunderstorms and potentially heavy rain near and along the divide Friday into Saturday morning. - Long range ensembles are showing potential for an extended hot, dry period through mid July. Our primary focus through this evening is monitoring the development of strong to isolated severe thunderstorms. Mostly sunny skies are seen in GOES Satellite imagery early this afternoon, with mesoscale analysis highlighting upwards of 500 J/kg of MLCAPE across west-central MT and north-central ID. The atmosphere will continue to destabilize through this afternoon, with convection developing between 1-3pm MDT across north-central Idaho and southwest Montana. Thunderstorms will track northward across west-central Montana between 4-7pm MDT. High resolution models along with instability and shear profiles all point towards discrete storms initially, evolving into linear segments as storms mature and grow through this evening. The last two runs of the HREF has pointed towards high probabilities (70-90%) for strong outflow winds across the Bitterroot Valley and points east along the I-90 corridor towards the divide. This matches up well statistical models and forecast soundings, therefore our confidence is higher than normal for these storms to occur and produce gusty outflow winds, with isolated gusts exceeding 60 mph with the strongest updrafts. Convection will continue overnight into Thursday morning, with additional rounds of storms across central Idaho into west-central Montana. Vertical profiles suggest instability and moisture will remain elevated, increasing the risk for dry thunderstorms. A trough within southwesterly flow will bring widespread showers and thunderstorms Friday afternoon into Saturday morning. This system will tap into sub-tropical moisture, with moisture climbing 125-150% of normal, leading to an elevated risk for heavy rain and localized runoff issues for flood prone areas, such as burn scars. Ensembles suggest the heaviest rain will focus across southwest Montana and along the divide, where NBM has a 40-50% chance of 0.50 inches or more of precipitation across the higher terrain, with probabilities dropping near 20% for valley areas. Furthermore, precipitation amounts have been trending higher across Flathead County, MT, especially in Glacier Park, where deterministic model runs suggest a mid-level low will deepen just east of the divide. This solution is worth monitoring closely, as currently just a minority of ensemble members are highlighting 1-2 inches of precipitation. In the longer term, global ensembles develop a broad ridge of high pressure across the western US, leading to a prolonged period of hot and dry weather July 9th through the 14th. However, it's worth noting, while statistical guidance show a similar pattern, they aren't as intense with the ridge or the heat. Any way you look at it, the preponderance of models point to an extended dry period of a week or more coming up. && .AVIATION...Confidence is high for showers and thunderstorms to develop across the Clearwater and Bitterroot Mountains and along the divide in southwest Montana between 02/1900-2100Z. Storms will grow into convective systems aided by modest instability and wind shear from an approaching trough, leading to an elevated risk for strong outflow winds given hot and dry air in the low levels. Thunderstorms will be in the vicinity of KSMN, KHRF, and KBTM by 02/2200Z, with high confidence (>70% probability) for outflow winds of at least 30kts from any storms that develop and move near area terminals. A few thunderstorms may approach severe criteria, with gusts exceeding 50kts. Another round of showers and thunderstorms will develop along a frontal boundary tonight, with activity continuing into early Thursday morning across north- central ID and west-central MT. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$ |