Area Forecast Discussion
Issued by NWS Missoula, MT
Issued by NWS Missoula, MT
163 FXUS65 KMSO 261909 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 109 PM MDT Sun May 26 2024 .DISCUSSION...GOES Satellite imagery this afternoon shows numerous fair weather cumulus clouds across the Northern Rockies. Forecast soundings suggest surface heating will allow for just enough instability for isolated showers to develop across eastern portions of Lake and Flathead Counties. Otherwise, valley areas can expect a mix of clouds and sun through the rest of the evening. A significant warming trend remains on track Monday into Tuesday as high pressure amplifies across the Great Basin and Northern Rockies. Confidence is high (probability >90%) for temperatures to reach into the 80s across valleys in western MT, with the lowest elevations in Idaho and Clearwater Counties hitting 90. Forecast models continue to highlight an increased risk for strong to potentially severe thunderstorms late Tuesday afternoon and evening. A Pacific trough will move onshore along the OR/WA coast, with atmospheric moisture, instability, shear, and lift within southwesterly flow creating a favorable set up for thunderstorms to develop across northeast OR during the early afternoon. Guidance suggests storms will then track northeastward into central Idaho and west-central and northwest Montana during the evening hours. The probability for strong thunderstorms, characterized by gusts greater than 40 mph, brief heavy rain, and small hail (0.75" or less in diameter), has increased into the 20-30% range across central Idaho and northwest Montana. Forecast details Wednesday into Thursday are beginning to become more clear. Ensemble guidance is trending away from a closed low scenario, with 70% of members suggesting a progressive trough passage, as seen in the 12z GFS/ECMWF. Impacts under this pattern will be characterized by temperatures 5-10F below normal, gusty westerly winds (20-35 mph in valleys), and widespread shower activity, with snow levels of 5,500-6,500 feet. The closed low scenario as seen with 20% of the members still brings the possibility for more widespread precipitation, with snow levels falling closer to 4,000-5,000 feet and pass level travel impacts. In the far extended, the dice are loaded towards above normal temperatures during the first week of June. This is well supported by ensemble means in strong agreement for high pressure across the Rockies, with a trough of low pressure remaining well off the west coast. /Lukinbeal && .AVIATION...Satellite imagery as of 26/1900Z shows widespread fair weather cumulus clouds tracking west to east across the air space. Westerly flow across mountain barriers is contributing to the development of mountain wave activity. Surface heating this afternoon will contribute to shallow instability across Flathead and Lake Counties, where isolated showers will periodically obscure terrain. Westerly wind gusts will continue through 27/0200-0400Z, with gusts of 15-20kts for area terminals. Stronger gusts of 25-30kts are expected along the divide and over the terrain. /Lukinbeal && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$