textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Winter weather advisories continue for heavy, wet snow showers through tonight.

- Warmer, drier weekend ahead.

- Next system coming early to mid next week with what looks like only minor impacts at this time.

A broad, closed low is migrating across the northern Rockies today and tonight and dragging some cooler air with it. It has been causing snow levels to drop through the day, though we've seen very little accumulation on the roads except with the front this morning and at high elevation locations like Georgetown Lake, Butte, and the passes along the Continental Divide. That is primarily due to the sunshine warming the roads, even through the clouds today. This evening however, that all goes away and there is potential for showers to cause accumulating snow. The main impacts will be in the higher elevation zones where we currently have advisories out, but some minor accumulations are also possible in the valleys too. The Clearwater Mountains of central Idaho are expected to be one of the hardest hit areas with about 0.5" per hour snow rates expected overnight with the wrap around moisture in up-slope flow.

As that low exits the region, a ridge builds in behind it setting up a warm, pleasant weekend weather wise. Temperatures will rise to the mid and high 60s in western Montana and into the 70s in central Idaho by Monday.

Ensembles are showing another trough and cold frontal passage next week around Tuesday or Wednesday. Currently the biggest disagreement among the ensembles is the timing. Most are showing a quick moving trough along the Canadian border with a trailing cold front across central Idaho and western Montana. This pattern, this time of year usually produces more wind than precipitation. The NBM is showing a 25% chance for wind gusts in the 30s in the valleys next Tuesday with this front. Some banded showers may also form in this pattern, but with current ensemble temperature forecasts, it would most likely be rain or snow that only accumulates in the mountains.

AVIATION

A cut off low migrating over the region today is causing showers with low ceilings and, at times, VLIFR visibility. The snow levels are dropping today as the low brings some colder air with it, so as the showers transition from rain to snow, they are causing poor visibility when they impact terminals. Visibility reductions to LIFR and below are only expected to last 15-45 minutes when they do occur. The wind profile currently isn't unidirectional or strong enough for showers to organize in to bands, so that will help keep the time of poor visibility conditions limited. Snow showers will last through the night, and areas the low has moved out of early tomorrow morning may experience some fog impacts, especially KGPI or KMSO. Any fog impacts will likely be short lived after the sun comes up. If fog does form, expect it to dissipate by 03/15Z or 03/16Z tomorrow.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Weather Advisory until 6 AM MDT Friday for Bitterroot/Sapphire Mountains...Butte/Blackfoot Region.

Winter Weather Advisory until noon MDT Friday for Potomac/Seeley Lake Region...West Glacier Region.

ID...Winter Weather Advisory until 5 AM PDT Friday for Southern Clearwater Mountains.