textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Prolonged atmospheric river event from Wednesday night through Saturday.

-Strong and potentially damaging winds late Wednesday night through Thursday, with the strongest gusts expected across northwest Montana and along the Continental Divide.

-Very difficult backcountry conditions due to strong winds and heavy snow, leading to localized blizzard conditions.

Forecast Changes Over Last 24-Hours:

As with all forecasts they evolve over time, this forecast is no different. Winds appear to have slightly weakened from 24-hours ago, yet will still attain strong to damaging speeds. Peak winds will still happen just after midnight tonight through Thursday afternoon. Be prepared for the potential of downed trees and power outages, as soils are not frozen and soil moisture is high for this time of year. Precipitation amounts have increased, especially in the Clearwater, Bitterroot, and Sapphire MTNS.

Small streams and creeks will likely see rapid rises and need to be monitored, please check local conditions if planning outdoor activities. Additionally, low lying and poor drainage areas may have ponding of water issues.

Short Term Forecast:

Satellite is showing a long fetch of subtropical moisture streaming into the Pacific northwest, this system will begin to affect our region this evening lasting into Saturday. Precipitation coverage and intensity will increase this evening as snow levels rise. North of I-90 snow levels will rise between 4000 and 4500 feet, before lowering into the valleys through Saturday. Elsewhere, snow levels will initially rise 4500 to 6000 feet, before lowering again by Thursday evening. The highest snow levels will occur in north- central ID, this is also the locations that will have largest variation in snow levels throughout the storm. Valleys even in northwest MT will be effected by downsloping, higher sun angles, and longer days. The only valleys that will likely receive snow accumulations will be northwest MT and only during overnight periods. Each morning Friday and Saturday a wet, heavy accumulation of trace to 3 inches is possible, depending on elevation.

All of our mountains are still on track to receive multiple feet of snow, lowest storm totals currently are in Lemhi County ID and the mountains of southwest MT. Blizzard conditions will be possible at times on Thursday, mainly in the mountains but potentially at Lolo and Marias Passes as well. The constant west winds and heavy, wet nature of the snow will produce avalanche concerns. Please check your local avalanche center recommendations before traveling or recreating in the back country.

Long Term Forecast:

The moisture plume appears to exit the region by late Saturday, but the Northern Rockies will remain in a breezy and active weather pattern through the remainder of the weekend and into next week.

AVIATION

Winds have weakened across the Northern Rockies due to the Jet Stream sagging south, but will begin to increase late this afternoon as the Jet Stream pushes north and increases in intensity. Additionally, after 12/0000z low level wind shear will be present at most terminals due to the increase in ridge top winds.

An atmospheric river is pushing into the region this evening, bringing increased precipitation coverage. Precipitation is expected to start as snow before transitioning to rain as snow levels rise.

Late Wednesday through Saturday, the Northern Rockies airspace will be impacted by a high intensity Atmospheric River system.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Winter Storm Warning from 6 PM this evening to noon MDT Saturday for Bitterroot/Sapphire Mountains...Lower Clark Fork Region...West Glacier Region.

High Wind Warning from midnight tonight to midnight MDT Thursday night for Butte/Blackfoot Region.

High Wind Warning from midnight tonight to 6 PM MDT Thursday for Flathead/Mission Valleys...Kootenai/Cabinet Region... Missoula/Bitterroot Valleys...Potomac/Seeley Lake Region.

Winter Weather Advisory until 6 PM MDT this evening for West Glacier Region.

ID...Winter Storm Warning from 5 PM this afternoon to 11 AM PDT Saturday for Northern Clearwater Mountains...Southern Clearwater Mountains.

Wind Advisory from 8 PM this evening to 11 AM PDT Thursday for Lower Hells Canyon/Salmon River Region... Orofino/Grangeville Region.

High Wind Warning from midnight tonight to midnight MDT Thursday night for Eastern Lemhi County...Western Lemhi County.