Helena, MT 59626 Weather

Key Messages

- Today will be the last mild day for awhile.

- Rain and snow develop over the CWA on Friday, along with much cooler temperatures.

- Generally dry conditions, along with more fall temperatures expected Saturday through Tuesday.

Discussion

- Meteorological Overview: The upper level ridge that has been over the CWA for the past few days will begin to move eastward today, as two upper level disturbances approach the CWA for Friday, one from the north and one from the south. Today will be the last well above normal temperature day for awhile, with many areas having high temperatures in the upper 60s or lower 70s today. There will be a few morning sprinkles over Southwest MT, but those should diminish early this morning. Otherwise, rain showers start to approach the CWA from the southwest this evening and overnight. At the same time, colder air will try to move southward from Canada overnight.

The colder air will be near the US/Canadian border by daybreak on Friday, as precipitation continues to overspread the western portions of the CWA. On Friday, expect the warmest temperatures in the morning, with temperatures falling during the afternoon hours as colder air moves in. Snow levels will start out above 10,000 feet tonight, but then fall through out the day on Friday, likely falling to near the valley/plains floor by Friday evening. Some short periods of heavy precipitation is possible on Friday as the front moves through. The front from the north will have some strong north winds, and these strong winds could mix down as the precipitation moves through. Thus a high wind watch has been issued for portions of North Central MT. At the same time, snow levels will be falling, with the best accumulating snowfall above 4500 feet. Thus some mountain ranges over Central/Southwest MT have a winter weather advisory in place for Friday afternoon/evening for several inches of snowfall. At lower elevations, given the short duration of the precip and the time it takes for the rain to change to snow, no advisory will be issued at this time.

This will be a very quick moving weather system, with both disturbances exiting the region by early Saturday morning. Generally dry conditions, but more fall like temperatures are expected from Saturday through Tuesday. The next weather system arrives next Wednesday, with a mix of rain/snow across the CWA.

- Forecast Confidence & Scenarios: Chance for thunder...there is a small chance for a lightning strike with the frontal passage on Friday. However, with a probability mostly less than 10 percent, thunder was just confined to far Southwest MT for now.

The main concerns on Friday will be wind, rain changing to snow, and snow accumulations.

Strong north winds are possible between Cut Bank and Havre on Friday, especially in the gap areas of the Sweet Grass Hills. with a 70 percent chance for high wind gusts in the favored windy spots between Cut Bank and Havre, a high wind watch has been issued for portion of the day on Friday for this area.

Aviation

22/12z TAF Period

Overall VFR conditions are expected through 00z Friday, before conditions slowly start to decrease. A few morning sprinkles around Ennis/West Yellowstone will generally diminish by 13z today. Otherwise, expect increasing clouds this evening, with rain and snow developing over the western portions of the CWA by 06z Fri. The rain and snow continue to push eastward overnight and should reach Central MT by mid day Friday. Snow levels will continue to lower to valley/plains floor by Friday evening. Expect ceilings to lower with IFR/LIFR conditions possible by Friday afternoon. Mountains/passes will start to become obscured after 00z Friday. Brusda

Preliminary Point Temps

GTF 73 43 53 28 / 0 20 100 70 CTB 69 36 47 22 / 0 30 100 10 HLN 70 43 52 25 / 0 20 100 80 BZN 70 40 53 23 / 10 10 100 90 WYS 62 32 46 18 / 10 70 100 100 DLN 67 42 50 27 / 10 80 100 90 HVR 73 40 56 24 / 0 0 90 80 LWT 74 44 63 23 / 0 0 90 100