Helena Valley Southeast, MT Weather

Key Messages

- Dense fog will continue to affect Southwest MT through this morning.

- Light rain and snow will move from west to east across the CWA overnight tonight.

- Another round of light rain or snow showers is expected to end the work week.

- Overall, afternoon temperatures will generally be near to a bit below normal all week.

Discussion

- Meteorological Overview: Low clouds and dense fog continue to affect Southwest MT this morning. Increasing high clouds will prevent the dense fog from expanding in areal coverage, but will also prevent the dense fog from burning off quickly this morning. Thus the no changes to the current dense fog advisory statement. Otherwise, the main concern later today/tonight will be the increasing chances for rain/snow as the next upper level trof approaches from the West. The heaviest precipitation should fall in the mountains with this system, with the southwest mountains being the favored area. Thus a winter weather advisory has been issued for tonight for the southwest mountains around Pony, Big Sky and West Yellowstone.

This will be a quick moving trof, with most of the precipitation ending by early Tuesday morning. For the rest of Tue/Wed, the airmass will remain a bit unstable for a few passing light rain/snow showers, but most/if any of the precipitation that falls should be in the mountains.

For later in the work week...mostly Thu into Fri...an upper level low will develop off the coast of the Pacific Northwest, but generally stall over that region. This will result in a moist southwesterly flow aloft developing over MT, which will allow for scattered rain/snow showers to move through the CWA from time to time. The upper level trof will begin to move slowly eastward over the weekend, and then moving across MT early next week. Thus the chances for light rain/snow showers will continue for several days.

Overall, afternoon temperatures will generally be a bit below normal across the CWA, with a few locations possibly seeing near normal temperatures Tue/Wed.

- Forecast Confidence & Scenarios: The main concern tonight will be the light snow across Southwest MT. Overall snow accumulations look to be on the lighter side, thus a winter weather advisory has been issued for one mountain zone...330...for this system. Rain is likely to change to snow at all elevations by Tue morning, but any snow accumulations at lower elevations generally look to be less than an inch at this time.

Periods of light snow are expected in the mountains later this week and into this weekend. Overall most of the snow accumulations will continue to be on the light side, but a winter statement might be needed from time to time over portions of the CWA later this week and into this weekend. Brusda

Aviation

26/12Z TAF Period

The main concern this morning will be areas of dense fog over Southwest MT, with visibility below 1/2SM at times. The fog will be a bit slow to burn off, thinking late morning, with low ceilings continuing into mid afternoon. Then the next round of light rain/snow moves into the western portions of the CWA by 00z Tue. Expect this band of precipitation to move from west to east across the CWA tonight. Mountains/passes will be obscured by clouds/precipitation across the CWA through the period. Brusda

Preliminary Point Temps

GTF 43 32 51 35 / 0 60 20 0 CTB 43 26 50 28 / 0 40 30 0 HLN 48 33 51 28 / 0 90 10 0 BZN 51 29 47 23 / 0 90 20 0 WYS 48 19 37 15 / 10 100 60 20 DLN 52 31 45 24 / 0 80 0 0 HVR 52 29 50 29 / 0 40 70 40 LWT 49 30 47 29 / 0 60 40 0