GNFAC Avalanche Forecast for Sun Mar 21, 2021

Not the Current Forecast

Good Morning. This is Alex Marienthal with the Gallatin National Forest Avalanche Forecast on Sunday, March 21st at 7:00 a.m. Today’s forecast is sponsored by Highline Partners and Gallatin Valley Snowmobile Association. This forecast does not apply to operating ski areas.

Mountain Weather

Since yesterday morning the mountains near Cooke City and West Yellowstone got 8-10” of heavy new snow, and near Bozeman and Big Sky got 3-5”. Overnight, wind increased to 10-15 mph with gusts of 25-35 mph, and this morning temperatures are teens to low 20s F. Today will be partly sunny with increasing clouds this afternoon. Temperatures will reach 20s F with west-northwest wind at 5-15 mph. There is a chance for a trace to 1” of snow tonight with more snow expected through tomorrow night.

Snowpack and Avalanche Discussion

All Regions

Recent heavy snow creates the main avalanche concern today. Skiers or riders can trigger avalanches that break within the new snow or on weak snow directly underneath. Since Friday night the mountains got 9-16” of snow equal to 0.9-1.5” of snow water equivalent (SWE). Moderate northwest wind last night drifted this snow into thicker slabs that are possible to trigger, and wind-loaded slopes are where you are most likely to find unstable snow.

Yesterday skiers in Hyalite triggered a 4” deep, 150’ wide avalanche from 150’ away (photo and info). I skied in the Bridgers (video) and Ian skied at Bacon Rind (video). We found the new snow was generally stable, but there had been no wind yet to form unstable slabs and we witnessed and received reports of variable conditions below the new snow. On slopes that face the sun and were affected by previous above freezing temperatures, the snowpack became warm and wet. The new snow insulated the unconsolidated wet snow which created an unstable setup like Ian describes in his video. Yesterday ski patrols triggered a couple small avalanches, during routine mitigation work, in isolated areas that had this wet, weak snow. On cooler, shadier and higher elevation slopes the snowpack is still cold and dry and there may be a thin layer of weak facets below the new snow. (Doug’s video from Centennials, video from Cooke).

Spring weather creates greater variability and uncertainty. Anticipate changes from slope to slope, and continuously assess the stability of the new snow before riding steep slopes. Dig down 1-2 feet and see what the new snow is sitting on. Pay attention to various conditions under your sled or skis, and have a safe alternate plan if you find signs of unstable snow. Recent heavy new snow makes avalanches possible to trigger today, and avalanche danger is rated MODERATE.

If you get out, please send us your observations no matter how brief. You can submit them via our website, email (, phone (406-587-6984), or Instagram (#gnfacobs).

Upcoming Avalanche Education and Events

See our education calendar for an up-to-date list of all local classes. Here are a few select upcoming events and opportunities to check out:

TOMORROW! March 20, 5:30 p.m., Snowpack Update for Bozeman Splitfest, online Link to Join HERE

March 24, 6 p.m., Free 1-Hour Avalanche Awareness, online Link to Join HERE

March 29, 6 p.m., Free 1-Hour Avalanche Awareness, online Link to Join HERE

April 5, 6:30 p.m. Forecaster Chat, online hosted by Uphill Pursuits, “Spring Snowpack and forecasting tools”.

The Last Word

Bears. Grizzly bears. They are waking up, stretching their limbs and looking for food. Walking the aisles in Safeway puts you on top of the food chain; when you are in the backcountry, they are. Carry a beacon, shovel, probe...and bear spray. Bozeman Daily Chronicle article.