515 FXUS65 KMSO 261939 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 139 PM MDT Sat Apr 26 2025 .DISCUSSION... KEY MESSAGES: - Showers and thunderstorms through this evening and again Sunday, with isolated outflow winds up to 40 mph. - North-northeast wind shift, with gusts of 25-35 mph along the divide, with choppy lake conditions Sunday evening. - Cooler and wetter pattern anticipated late Sunday into Monday. Snow accumulations above 5,500 feet across Lemhi County and along the Continental Divide. Satellite imagery this afternoon shows a mid-level circulation over the northern Bitterroot Mountains, with numerous showers and isolated thunderstorms developing in the warm sector to the south and east. Forecast soundings suggest modest instability through this evening across north-central Idaho and west-central Montana, with dry lower levels of the atmosphere creating an ideal set up for areas of outflow winds of 30-40 mph. Showers and thunderstorm life cycles will be short lived given a lack of vertical wind shear, therefore outflow boundaries will tend to be more localized in nature, with longer lived outflow boundaries in north- south oriented valleys, such as the Bitterroot. A closed low over CA/NV will move northeastward Sunday into Monday, with moisture increasing tonight into Sunday morning. Therefore, another round of shower and storm activity is expected Sunday, with outflow winds of 30-40 mph, brief heavy rain, and lightning being the primary storm threats. The closed low will stall into southeast Idaho Sunday evening into Monday morning, with a cold front dropping southward from Canada. A north- northeast wind shift is expected as the front arrives across northwest Montana and along the divide Sunday evening. This wind shift will bring choppy conditions to area lakes, including Flathead Lake, Georgetown Lake, and bodies of water in the Seeley-Swan Valley. Precipitation will focus across Lemhi County into southwest Montana Sunday into Monday morning, where a north-northeast gradient will bring the highest precipitation totals along the divide. Precipitation amounts will range from 0.10-0.30 inches in the valleys, with 0.50-1.00 inches in the higher terrain. Snow will focus above 5,500 feet, with minor slushy accumulations across MacDonald, Homestake, Lost Trail, and Bannock Passes. Remote mountain areas above 6,500 feet in Lemhi County will see the highest snow amounts, with six inches or more of snowfall. By Tuesday and Wednesday next week, model guidance suggests another trough of low pressure will move through the area from the northwest. Breezy west-northwest winds will develop along with scattered shower activity. A warming trend is anticipated by Thursday into Friday, with ensemble models pointing towards high confidence (>90% chance) for a broad ridge of high pressure. && .AVIATION...Showers and isolated thunderstorms will become more numerous through the afternoon and early evening, then decreasing in coverage significantly after 27/0300z. KMSO, KHRF, KBTM and KSMN have the best chances (30 to 50 percent) of seeing a brief shower or thunderstorm, while KGPI has a limited threat (20 percent). In addition to lightning, storms will be capable of erratic wind gusts up to 35 kts locally. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$