Area Forecast Discussion
Issued by NWS Missoula, MT
Issued by NWS Missoula, MT
361 FXUS65 KMSO 130916 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 316 AM MDT Thu Jun 13 2024 .DISCUSSION... Update: Only minor changes made to yesterday afternoon`s discussion through the Saturday timeframe. Updates have been made to the Sunday through Tuesday portion of the discussion to reflect growing confidence in a closed low scenario for early next week. The Northern Rockies will remain under the influence of a ridge of high pressure through Friday, leading to a period of warm and dry weather. Generally light winds are expected today, before westerly winds kick in Friday as an upper level jet begins to move overhead associated with a Pacific trough approaching the OR/WA coast. Valley areas will experience gusts of 15-25 mph. Higher gusts will focus across the Mission Valley and Lemhi County, where NBM probabilities for gusts of 35 mph or greater reach 50-60%. A significant change will impact the Northern Rockies this weekend into early next week. The aforementioned Pacific trough and surface cold front will move across eastern Washington into western Montana Saturday. Westerly winds will increase along and behind the cold front Saturday afternoon and evening, especially across the US-93 and I-90 corridors, where NBM probabilities for gusts of 40 mph or greater hit 40-60%, with higher probabilities of >75% across Lemhi County and the I-90 corridor from Deer Lodge through Butte and Lemhi County in Idaho. Furthermore, in addition to modest pressure rises associated with the front, the threat of gusty winds is bolstered by the potential for convective mix winds with showers and thunderstorm activity. The forecast becomes challenging and complex late Sunday into Tuesday. Model guidance continues to display a range of potential outcomes as a secondary trough moves across the region. Roughly ~75% of ensemble members now show a closed low scenario, with widespread precipitation and lowering snow levels. In fact, the coldest solutions show a 10 to 20 percent chance that snow levels could lower to 4,500-5,000 feet by Tuesday morning. Under this solution, theres concern for utility infrastructure and significant impacts to higher elevation areas (>5,000 feet elevation). Snow loading from heavy wet snow will be capable of damaging vegetation and causing difficult travel across backcountry roads. Higher end snow totals within the NBM (10% chance to exceed or hit amounts) reach 1-2 feet above 6,000 feet across the Sapphire Mountains, Anaconda-Pintler and Flint Creek Ranges, as well as for the highest terrain in Glacier National Park. The other 25% of ensemble members show a progressive trough scenario, with higher snow levels of 6,000+ feet, showers, and cooler temperatures. Impacts under this case would mainly target the higher peaks and backcountry areas. Nonetheless, even under the progressive trough scenario, recreation will be impacted and those heading into the backcountry should be prepared for cold, windy, and generally unpleasant conditions for June. && .AVIATION...High pressure will build over the region today, bringing generally sunny skies and light, terrain driven winds. By Friday, winds aloft will increase significantly from the southwest ahead of an approaching weather system. These winds will be able to mix down into the valleys by Friday afternoon, with gusts to 25kts common across all of western Montana and north central Idaho. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$