The Flathead Avalanche Center issued a special avalanche warning Friday after nearly 2 feet of new snow accumulated in the mountains of Northwest Montana.

A storm on Thursday dumped about 20 inches of snow along Going-to-the-Sun Road and in the Middle Fork area south of Glacier National Park. Numerous large avalanche debris piles were seen below steep terrain in these areas. Backcountry travelers on Thursday reported easily triggering wet and loose avalanches at mid elevations in the Middle Fork, and a reactive snowpack was observed on steeper terrain at Whitefish Mountain Resort, where about 20 inches of snow also accumulated.

The significant amounts of new snow combined with warming temperatures this weekend will create dangerous avalanche conditions, especially on Saturday, the avalanche center warned. Human-triggered and natural slides will become likely during day-time warming.

“Keep your head on a swivel as you travel through the mountains over the next few days, being especially wary of the steep slopes above you holding on to copious amounts of fresh snow,” avalanche forecaster Zach Guy warned.

Guy added that “roller balls and pinwheels” of snow coming off steep slopes “are Mother Nature’s warning sign before she unloads a cement mixer full of wet, heavy debris down on you. You want no business getting tangled in one of these types of slides.”

He also said that people biking the Sun Road this weekend should be avalanche aware at the higher elevations.

The section of the Sun Road between Lake McDonald Lodge and Rising Sun is closed to vehicles due to plowing. Hiking and biking access on the west side is to the Logan Pit area, approximately 10 miles past the vehicle closure, while the road crew is working.

Check the Sun Road status at www.nps.gov/applications/glac/roadstatus/roadstatus.cfm