Area Forecast Discussion
Issued by NWS Missoula, MT
Issued by NWS Missoula, MT
627 FXUS65 KMSO 160816 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 216 AM MDT Mon Sep 16 2024 .DISCUSSION...Southerly flow aloft will allow for increasing moisture across western Montana and north central Idaho ahead of a cut off area of low pressure currently located over central California. This is a favorable pattern for the development of showers and thunderstorms, particularly this afternoon and evening. There is little in the way of shear, which means storms will likely not be overly strong today. However, with moisture amounts increasing to 150-200 percent of normal and storm motion of only 10-20 mph, very heavy rain will be the main concern. In particular, the latest high resolution models show a 20-40 percent chance of hourly rainfall rates exceeding 0.50" in Idaho County. Flood prone basins will need to be monitored this afternoon, including the Williams Creek and Elk Horn burn scars from 2022 and 2023. Forecast models are beginning to come into better agreement with regards to the closed low track as it ejects northeastwards through central Idaho into eastern Montana Tuesday into Wednesday. This more southern track has caused precipitation amounts in the forecast to trend lower, especially across northwest Montana near the Idaho panhandle. While most all of western Montana and north central Idaho can expect precipitation, the most likely area to receive 0.50" of rain or more (70 to 80 percent chance) through includes Idaho County in Idaho and locations generally along and east of the Highway 93 corridor in western Montana. Precipitation will largely come to an end for Thursday into the early part of the weekend, with temperatures largely rebounding to seasonal normals in the upper 60s to mid 70s. Then ensembles are showing a 10-15 percent chance of a high impact, high elevation snow even late next weekend in northwest Montana. There is a 10-15 percent chance for a foot of snow above 7,000 ft in Glacier National Park. We`ll continue to watch that potential very closely. && .AVIATION...Southerly flow aloft ahead of a cut off low pressure system over central California will provide conditions favorable for showers and thunderstorms today. Showers and isolated thunderstorms currently exist across Lemhi County in Idaho, with wind gusts up to 35 mph being noted. This line will slowly shift northwards into southwest Montana through 16/1500z before generally fizzling out around KMSO. Thunderstorms will then become more likely after roughly 16/2100z across all areas other than far northwest Montana. Slow moving thunderstorms will be capable of very heavy rainfall rates, generally along and south of the I90 corridor, including in the vicinity of KMSO, KHRF and KBTM. A few gusts to 40 mph could also be a concern with storms. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$