textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- Near-record heat today: Highs will reach the 80s to low 90s. Rivers remain dangerously cold and fast; use extreme caution near the water.

- Two distinct wind threats Wednesday: 1. Damaging thunderstorm winds: Gusts over 60 mph are possible Wednesday afternoon, mainly from Deer Lodge to Butte and southward. 2. Strong cold front winds: Gusty winds will arrive Wednesday afternoon and evening, creating dangerous conditions for boaters on lakes and increasing fire danger in southwest Montana.

- Drastic temperature drop and hypothermia risk: Summer conditions end Wednesday night. Mountain highs will crash into the 40s on Thursday and the 30s this weekend with accumulating snow. Backcountry users must prepare for winter conditions. Frost is possible by Sunday morning.

Today (Tuesday):High pressure brings one last day of near-record heat, with highs in the 80s and low 90s. Rapid snowmelt continues to keep rivers dangerously cold. Cold water shock is a severe hazard for anyone on the water today; even strong swimmers can be quickly incapacitated by these temperatures.

Wednesday and Thursday (The Big Transition):Weather conditions will change abruptly on Wednesday as a strong cold front moves through. Missoula and Kalispell will likely see their warmest temperatures early in the day before readings begin to fall. The front is expected to reach the Camas Prairie in Idaho by mid- morning, west-central Montana by early afternoon, and the Butte area between 6:00 p.m. and 9:00 p.m. MDT.

The Dual Wind Threat:

Cold Front: Wind is the primary hazard on Wednesday. While scattered storms are possible, a rapid increase in air pressure behind the front will cause westerly wind gusts of 35 to 45 mph. These winds will create dangerous waves for small boats on Flathead Lake and other area waters. Expect some broken tree branches and isolated power outages.

Thunderstorms: Showers and storms will form as early as noon over Lemhi County, moving northeast at 30 to 45 mph. Because the air is so dry, these storms could produce intense, damaging wind gusts. The highest risk is along Highway 93 in the Bitterroot and Missoula Valleys, extending east to the Continental Divide. This will create dangerous cross-winds on north-south highways and increase fire danger in southwest Montana.

The Rain/Snow Shift: Rain and snow will focus primarily on the northern two-thirds of the region late Wednesday. Valleys may see up to 0.30 inches of rain, while mountains could receive up to 0.75 inches of liquid. As a cold storm system moves over the area, snow levels will drop to near 5,000 feet. Several inches of new snow are expected in the high country of Northwest Montana by Thursday morning. Backcountry users will encounter slushy snow on high-elevation roads. Combined with winds and temperatures in the 40s, this creates a high risk for hypothermia.

Friday through the Weekend (Return to Winter): An unusually strong storm system from the Gulf of Alaska will settle over the Northern Rockies this weekend. Bitterly cold air will drop snow levels to 4,000 feet. Mountain highs will stay in the 30s, while valleys will struggle to reach the 50sabout 15 degrees below normal. Unstable air will trigger widespread showers all weekend. In the valleys, heavy bursts of soft hail (graupel) are possible.

Bottom Line for the Weekend: Pack for winter if you are heading outdoors. The combination of wet snow, wind, and near-freezing temperatures is dangerous for those only prepared for spring. By Sunday and Monday morning, temperatures may drop low enough to cause frost, which could damage sensitive plants.

MSO WATCHES/WARNINGS/ADVISORIES

MT...Wind Advisory from 9 AM Wednesday to midnight MDT Wednesday night for Kootenai/Cabinet Region...Lower Clark Fork Region.

Wind Advisory from noon Wednesday to midnight MDT Wednesday night for Bitterroot/Sapphire Mountains...Butte/Blackfoot Region...Flathead/Mission Valleys...Missoula/Bitterroot Valleys...Potomac/Seeley Lake Region...West Glacier Region.

Winter Weather Advisory from midnight Wednesday night to 3 PM MDT Thursday for West Glacier Region.

Red Flag Warning from noon to 9 PM MDT Wednesday for Deerlodge/West Beaverhead...East Beaverhead.

ID...None.