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FXUS65 KMSO 141943 AFDMSO

Area Forecast Discussion National Weather Service Missoula MT 143 PM MDT Fri Jun 14 2024

DISCUSSION
A low pressure circulation moving into the Pacific Northwest will bring shift to southwesterly flow aloft today.
Increasing southwesterly winds and isolated precipitation for southwest Montana will grace the forecast for the remainder of today. On Saturday, the low moves inland and will push a cold front across the Northern Rockies. This frontal passage will result in increasing westerly winds, especially for Flathead Lake and the Mission Valley, as well as Lemhi County. High resolution guidance has backed off on winds slightly since the last forecast, showing about 10 to 20 percent chance for gusts to exceed 40 mph in the valleys of western Montana. Gusts are a little more impressive in Lemhi County and along the Continental Divide. The front will also bring chances for precipitation and cooling temperatures on Saturday. There will be a chance for isolated thunderstorms (20-30 percent) for western Montana and north- central Idaho on Saturday afternoon. Thunderstorm outflow winds would further enhance wind speeds.

After a brief period of clearing on Sunday, a significant wet and cold weather system is expected Monday into Tuesday, with a general consensus (around 70-80 percent of model solutions)
supporting a closed low feature moving through the region.
Current model solutions show a roughly 30 to 40 percent chance that liquid precipitation amounts will be 1.00 inch or more along the Continental Divide into southwest Montana and extending westward into eastern portions of Idaho and Clearwater County.
Snow levels are tricky with this particular system as forecast models are notoriously biased too warm with late season closed low systems such as this. Areas that receive the heavier precipitation will likely see snow levels driven to 5000 feet or lower. There is insufficient confidence in either low pressure track or intensity currently, but you are encouraged to follow future forecasts as 1 to 2 inches of heavy, wet snow on trees with leaves could easily cause broken branches leading to localized power outages with winter driving conditions over area mountain passes.

For terrain above 6000 feet, a trace to 12 inches of snow is possible. Snow amounts will vary with snow levels, where uncertainty is still high. The message for backcountry travelers at the current forecast lead time is to be prepared for winter conditions on Monday afternoon through Tuesday morning and to continue to monitor the forecast through the weekend. While snow amounts may not be what we see in mid-winter, the snow will be very wet and heavy. Wet snow falling on trees in full bloom will result in plenty of downed trees and limbs, potentially blocking Forest Service roads. Closer to towns, expect downed trees and limbs to result in power outages. The higher terrain of the Bitterroot, Anaconda, and Pintler Mountains, Bob Marshal Wilderness, and Glacier National Park Region has the best chance of receiving a foot of snow or more. We have extended the Winter Storm Watch issued on Thursday to include the Sapphire and Bitterroot ranges including Skalkaho Pass.



AVIATION
Westerly winds will gust to about 25-30 knots this afternoon across all of western Montana and north central Idaho.
Increased cloud cover is also anticipated today. A few showers or isolated thunderstorms are not out of the question, primarily southeast of a line from KHLN to KHRF to KGIC. Showers or thunderstorms will be capable of producing a few localized wind gusts to 35 kts. Westerly winds will again gust in excess of 25 knots on Saturday with a frontal passage in the morning. Expect increasing clouds and chances for rain showers to begin on Saturday morning, also with the frontal passage.



MSO WATCHES/WARNINGS/ADVISORIES
MT...Winter Storm Watch from Monday afternoon through Tuesday evening for West Glacier Region.

Lake Wind Advisory from 11 AM to 10 PM MDT Saturday for Flathead/Mission Valleys.

Winter Storm Watch from Monday evening through Tuesday evening for Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...Potomac/Seeley Lake Region.

ID...Wind Advisory from noon to 8 PM MDT Saturday for Eastern Lemhi County...Western Lemhi County.

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