Area Forecast Discussion
Issued by NWS Missoula, MT
Issued by NWS Missoula, MT
090 FXUS65 KMSO 171854 AFDMSO Area Forecast Discussion National Weather Service Missoula MT 1254 PM MDT Tue Sep 17 2024 .DISCUSSION...A cut-off low pressure system will continue to spin over east-central Idaho through the evening today, that will bring widespread wetting rains across much of western Montana and north-central Idaho through early Wednesday. In the more immediate time-frame, locally heavy rainfall will be possible on the northern periphery of the low across northwest and west-central Montana this afternoon and evening. Currently, there is a 40% probability locations along and east of Highway 93 could see rain rates up to, or exceeding 0.50"/hr. Flood prone areas, such as steep terrain and burn scars will be the primary areas of concern for rock and mudslides (Glacier National Park for example). The low pressure system will move into western Wyoming and central Montana overnight, that will transition most of the precipitation to locations along the Continental Divide, where probabilities for 24hr rainfall amounts totaling 1.00", range from 60-70%. The probabilities quickly drop off to 30-40% for areas along highway 93. Locations in north-central Idaho, west of the Bitterroot Crest, will miss out on the higher amounts, where probabilities for even 0.25" are as low as 10-20%. Some clearing is expected Wednesday night with high valley locations cooling down into the 30s, and upper 20s in the Dixie, Idaho area. Patchy fog Thursday morning will give way to a gorgeous day across the Northern Rockies with temperatures warming into the 60s and 70s. Breezy westerly winds 10 to 20 mph will develop in the afternoon and evening. Ensemble guidance continues to trend away from the colder system over the weekend, with roughly 80% of the ensembles showing a west-northwest flow pattern. This translates to partly cloudy conditions, with temperatures in the upper 60s/low 70s in western Montana and upper 70s/low 80s in north-central Idaho. && .AVIATION...Shower and embedded thunderstorm activity will increase in coverage by 17/2000Z(mid-afternoon) and continue through 18/0400Z (10 pm MDT this evening). Locally heavy rain, lower ceilings/visibility, lightning and gusty winds to 30 knots are possible, especially from Clearwater County, Idaho to areas north and east into northwest Montana. A departing low pressure area will keep persistent showers going through Wednesday with mountain obscurations and lowered ceilings at times. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. && $$