The southern half of the Bitterroot Valley and points east could start seeing mountaintop snow by Tuesday as a wet weather system moves into southwestern Montana.

Up to 4 inches of snow may land on Lost Trail Pass and other areas above 6,000 feet elevation, according to an alert from the National Weather Service.

Missoula and parts of Lake County could see heavy valley rainfall and cold temperatures Tuesday and Wednesday. Travelers should be alert for sloppy roads on Lost Trail, MacDonald, and Homestake passes in Montana, as well as Gilmore Summit and Bannock Pass in Idaho. Lemhi County could feel wind gusts of more than 30 mph on Monday and Tuesday.

That means it’s time for hardcore gardeners to pull those last tomatoes off the vine and gather mulch for winter defense.

“It’s been so nice up to now,” Missoula County Extension Office horticulturalist Sandy Perrin said. “We haven’t had a real hard frost yet, but we’re still way behind on average moisture for the season. A lot of people forget their trees need a little water later in the fall.”

Perrin said deciduous trees benefit from a good soaking once their leaves have fallen – enough water to moisten the ground about a foot deep. Evergreens also overwinter better if they get a final shot of moisture. Weather fronts like the one forecast for this week help, but many areas still run a deficit after this relatively dry summer.

That water bank account should get some good deposits this fall and winter, according to state climatologist Kelsey Jensco at the University of Montana. Although an expected shift from the warm/dry El Nino pattern to the cool/wet La Nina appears to have stalled, that neutral zone should still bring steady moisture.

“When I look across the one-, two- and three-month forecasts and precipitation models, almost all of Montana is covered in green,” Jensco said on Monday. “That summarizes the fact we should expect higher-than-normal precipitation.”

While those short- and long-term climate models agree on moisture, there’s less confidence on what kind of moisture might come. That’s because the temperature models are wobbling around an equal chance of above- or below-normal conditions, which determine whether storms blowing in from the Pacific come loaded with rain or snow.

For the rest of October, the forecast offers a 30 percent to 40 percent chance of above-average moisture. That bodes well for hunters and skiers who look forward to moist conditions later in the fall.

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