578 FXUS65 KMSO 280851 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 251 AM MDT Thu Mar 28 2024 .DISCUSSION... Surface pressure analysis early this morning shows a surface low moving northeastward across southern Idaho. A mesoscale precipitation band has developed west-northwest of the lows center as seen in regional radar imagery. The latest round of model guidance suggests this low will move across eastern Lemhi County between 400-700 AM MDT, before reaching southwest Montana thereafter. Precipitation will spread across the southern Clearwater Mountains, the Bitterroot/Sapphire Mountains, and across Lemhi County and southwest Montana with snow levels initially around 5,000-5,500 feet. High resolution guidance suggests moderate precipitation intensity will help drive snow levels down towards 4,000-4,500 feet. A short period (1-2 hours) of moderate snow will impact Montana 1 from Drummond to Georgetown Lake and I-90 from Garrison Junction through Butte. Winter weather advisories remain in effect for the southern Clearwater Mountains and Bitterroot/Sapphire Mountains Mountains through this morning, where higher confidence exists for winter driving conditions across Lolo and Lost Trail Passes. The atmosphere will destabilize this afternoon as a Pacific trough passes overhead. Modest instability will produce vigorous mountain snow showers. Valley areas will see a mix of rain, snow, and graupel from convective showers. The primary impacts will be short lived visibility reductions, with periods of slushy roadways at the higher elevations. As mentioned in previous discussions, model guidance continues to show high confidence for a digging Pacific low to move into southern California Friday into the weekend. The Northern Rockies will remain under the influence of a broad trough under southwesterly flow keeping showers in the forecast, mainly across the higher elevations. The Pacific low will begin to track eastward into the great Basin on Sunday. Model guidance continues to advertise a mid-level low moving into northern UT, southern ID, and WY. Its worth highlighting the low probability snowfall event (15% percent) for Lemhi County and southwest Montana continues to exist within model cluster members. This snowfall event would occur if this mid-level low tracks further north; however, most guidance (85% of members) suggest this will not be the case. Long range models are in strong agreement for a ridge of high pressure to develop over the region early next week (Monday- Tuesday), bringing warmer and drier conditions. Overall however, model ensembles indicate this being a shortlived ridge, with nearly 80 percent of forecast models returning us to cool, showery and potentially quite windy conditions by Thursday (April 4). /Lukinbeal && .AVIATION...Precipitation continues to spread across the Clearwater Mountains, Lemhi County, and portions of southwest Montana early this morning as a surface low approaches into central Idaho. Precipitation rates will increase between 28/1100-1800Z as the low pushes across eastern Lemhi County into southwest Montana. Snow levels will fall from 5,000-5,500 to 4,000-4,500 feet, with a mix of rain/snow at KSMN and KHRF, bringing lower ceilings and visibility reductions. Confidence is high for at least IFR visibility reductions at KBTM this morning as snow spreads across the area with the low passing to the south. Furthermore, there is a 20-30% chance for a brief period of moderate to heavy snow at KBTM between 28/1500-1700Z. Convective showers will develop across the Northern Rockies airspace this afternoon, with brief visibility reductions being possible for all terminals from a mix of rain, snow, and/or graupel. /Lukinbeal && .MSO WATCHES/WARNINGS/ADVISORIES... MT...Winter Weather Advisory until noon MDT today for Bitterroot/Sapphire Mountains. ID...Winter Weather Advisory until 11 AM PDT this morning for Southern Clearwater Mountains. && $$ |