textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Slippery Travel: Pockets of light freezing rain in valleys and snow at pass level are possible Thursday, Friday, and Saturday mornings.

- Warming Trend: There is a 70-90% chance that many valley locations will reach 60 degrees mid-week next week.

Satellite imagery early this morning depicts a closed low pressure circulation over the Gulf of Alaska and a weak ridge over the western US. The low will push Pacific moisture onshore today, resulting in light snow for the Idaho-Montana border and Flathead Valley. Appreciable accumulations will be limited to the mountains. The Swan, Mission, and Cabinet ranges will be favored for about a half foot of snow in the higher elevations. As far as the valley locations are concerned, model soundings indicate some drying aloft, which will be conducive to light freezing rain this morning. This same setup is more evident for Friday and Saturday mornings. Northwest Montana and Clearwater County will be favored for slippery conditions each morning (10 - 20% chance). If you have travel plans, please check road conditions in the morning before departing.

While the low pressure continues to spin over the Pacific, the ridge along the coast will amplify and strengthen going into the weekend. Daytime high temperatures will reach the 40s and 50s across many valley locations. A brief breakdown of the ridge comes on Monday, as a shortwave trough moves through the Northern Rockies. Snow levels stay high though, above 4,000 to 4,500 feet, so valley precipitation will be in the form of rain while mountains see light snow. More pronounced high pressure will build back on Tuesday. Forecast models show a 20 to 30 percent chance of highs reaching 60 degrees in the Camas Prairie, Idaho, as well as the Mission, Deer Lodge, and Bitterroot valleys by the middle of next week.

AVIATION

Light precipitation will bring brief reductions in visibility to KMSO and KGPI this morning. There will be a slight chance (less than 5%) for precipitation to come as freezing rain. A midlevel stratus deck will persist at all Northern Rockies airfields throughout the day. Expect precipitation to obscure terrain over the Bitterroot, Sapphire, and Cabinet ranges, along with gusty west winds over mountain crests, especially the Continental Divide, where gusts will reach 30-40 kts this afternoon. Chances for freezing rain increase on Friday morning to about a 10-20% chance for KGPI and KMSO.

HYDROLOGY

Due to persistent cold temperatures, area rivers and streams are beginning to see significant ice build up in Lemhi County, Idaho. Some properties are experiencing minor flooding downstream of the Lemhi River gauge, near Lemhi. Watch for increased river levels as we approach the expected warm temperatures this weekend and early next week.

MSO WATCHES/WARNINGS/ADVISORIES

MT...None. ID...None.