textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Localized strong winds gusting over 50 mph with a 40-50% chance of gusts over 60 mph will affect the area around Grangeville, Idaho this morning.

- Today, the first in a series of waves will impact the region causing significant mountain snow and travel delays over the mountain passes.

Strong southerly winds will interact with the mountains south of Grangeville, Idaho today causing a downslope wind storm. A high wind warning has been issued for that area and will last through noon PST today.

Also arriving today is the first in a series of waves which will bring some moisture to the region. This pattern looks like an atmospheric river, but the amount of moisture and the rate that it's coming in doesn't quite reach the bar we've set to be called an atmospheric river in this region. So it's going to bring rain and impactful snow to the mountains, but nothing too extreme. This first wave will last through today, with a little bit of a break as the moisture continues but at much lower levels on Friday, and the it strengthens again on Saturday and Sunday.

Through tonight we expect 3-5 inches on the low end up to 8-12 inches on the high end of the forecast for Lolo and Lookout passes. For the weekend through Monday morning, the low end forecast for those same passes is 10-12" and the high end forecast is 20-28 inches over a 72 hour period. Snow levels remain high through early next week, and downsloping or the rain shadow effect means there will be much less snow in the valleys. So the Bitterroot, Missoula, and Mission valleys have less than an inch in the forecast for a high end event, while the Flathead valley is looking at up to 3 inches for a high end event. On the low range of the forecast the snow levels remain high and it's all rain in the valleys.

Low temperatures each morning in the valleys will be around or just below freezing, so with any moisture there is also a risk for icy conditions to develop overnight and for the morning commutes. Travel safely.

AVIATION

Today marks the beginning of a wet period for central Idaho and western Montana. An atmospheric river like pattern is setting up over the region, but it won't quite be strong enough to be classified as an atmospheric river. As a result snow and rain showers today will cause VFR conditions at times. Area terminals are mostly located in valleys, and downslope flow combined with rising snow levels today will keep the impacts fairly limited. Overnight lows Thursday night into Friday will be below freezing meaning there is potential for ice on any wet surfaces. Friday morning, between 27/07Z and 27/13Z will be ripe for fog formation at area terminals due to recent moisture and a weakening pressure gradient.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory until 2 PM MST this afternoon for Kootenai/Cabinet Region...Lower Clark Fork Region.

Winter Weather Advisory until 2 PM MST this afternoon for Bitterroot/Sapphire Mountains.

ID...Winter Weather Advisory until 1 PM PST this afternoon for Northern Clearwater Mountains...Southern Clearwater Mountains.

High Wind Warning until noon PST today for Orofino/Grangeville Region.