textproduct: Missoula

DISCUSSION

KEY MESSAGES:

- A cold front is moving through today (Monday), bringing cooler, showery, and breezy conditions.

- A low pressure system will impact the region late Wednesday into Friday.

Today (Monday), a cold front currently extends from north-central Idaho into west-central Montana. The front will continue to push southward throughout the day. Most of the rain and snow will fall along the front, with a few scattered showers lingering behind it. Breezy conditions will develop across the region today with wind gusts up to 30 mph, and higher gusts in the mountains. The biggest impact of these winds will be choppy conditions on Flathead Lake.

Scattered mountain snow and valley rain will linger over portions of the Northern Rockies during the day Tuesday, mainly for locations south of the Interstate 90 corridor. Breezy west to southwest winds with gusts between 20 to 25 mph will also develop in the afternoon.

By Wednesday, a low pressure system will strengthen off the Pacific Northwest coast. This will set up southwest flow into the Northern Rockies region, bringing more rain and snow. By Thursday, cold air associated with this low will move over the region and snow levels will drop to 3000 to 4000 feet in north-central Idaho, bringing accumulating spring snow to many higher-elevation valleys. Portions of the lower elevations of central Idaho, including Grangeville, have about a 50 percent probability of seeing accumulating snow, while the most likely snowfall amount for the mountains of central Idaho is closer to the 5 to 7 inch range. Elevations above 5000 feet south of Highway 12 could see upwards of a foot of snow.

As the low pressure system moves east into eastern Idaho and southwestern Montana, colder air will move in as moisture wraps around the system over western Montana during the day Friday. The latest forecast models show a TROWAL (a narrow area of intense precipitation) developing over western Montana early Friday morning. Historically, the exact location where a TROWAL develops is difficult to pin down even 24 hours out. The most likely location for development will be areas east of the Highway 93 Corridor and along the Continental Divide. Anywhere from 5 to 12 inches of snow is possible for locations under the heavier precipitation by the end of the day Friday. Valley locations outside of this narrow band will see a trace to a couple of inches, with the mountains seeing around 6 inches. The heavy, wet nature of the snow is likely to build up on trees, creating potential tree damage and power outages. Stay aware of forecast updates as we progress through the week. If you have plans to travel east over the Continental Divide later this week, plan ahead and make sure you pack supplies in the event you experience extensive delays over mountain passes.

A much quieter weather pattern will develop over the Northern Rockies this weekend as a weak ridge of high pressure moves in. Temperatures will trend warmer, with afternoon highs running 5 to 10 degrees above normal for this time of the year Saturday through Monday.

AVIATION

The band of rain and snow associated with the cold front currently extends over southwest Montana. The front will slowly push south through the rest of the afternoon and this evening. Light to moderate snow is periodically reducing visibility at KBTM and over surrounding terrain, along with west- northwest wind gusts of 20 to 25 knots. Rain and snow will begin tapering off by 31/0000Z this evening. All other terminals in the area will see scattered mountain obscuration and breezy northwest winds around 25 knots through 31/0200Z.

MSO WATCHES/WARNINGS/ADVISORIES

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