Those spending their Thursday boating on Flathead Lake or hiking in the mountains should prepare for potentially severe weather moving into Northwest Montana this evening.

Beginning at around 7 p.m., sustained winds from 30 to 40 miles per hour on Flathead Lake are forecast to produce waves up to five feet, according to Ryan Leach, a meteorologist with the National Weather Service office in Missoula.

“With it being the recreation season, we feel the lake is really vulnerable,” Leach said. “The lake is at full pool and with the water really warm right now, combined with a cool, windy weather system, it has the potential to produce a lot of wind.”

Motorists driving on Montana 35 as it winds along the east side of the lake should also stay alert for falling trees as winds pick up. Leach characterized the weather system as a “back-door cold front,” with cold air spilling over the mountains and through valleys from the northeast and the north. Drivers should also be cautious while traveling through Bad Rock Canyon and other wind-prone areas.

The main wind event is predicted to settle down by about 10 p.m. and could deliver scattered thunderstorms.

Leach added that earlier predictions of high-altitude snow in Glacier National Park were marked by uncertainty, and significant snowfall isn’t expected west of the Continental Divide. Some snow is possible, however, and hikers should be prepared for sudden changes in the weather this evening.

“If you’re up there over 8,000 feet and you’re going to be hiking, it’s going to be wet, cold, raw and there’s going to be a potential for snow,” he said.

The Weather Service is forecasting a sunnier Friday, but expects temperatures to peak in the low 70s and include some light breezes throughout the day. The sunshine should continue through the weekend, a high of 84 degrees on Saturday and temperatures hitting 90 on Sunday.