GNFAC Avalanche Forecast for Thu Mar 13, 2025
This is Mark Staples with the avalanche forecast for Thursday, March 13th, at 7:00 a.m. sponsored by Polaris and the Avalanche Alliance. This forecast does not apply to operating ski areas.
This morning snowfall has already started near Island Park, West Yellowstone and Big Sky with a trace to 1” accumulating so far. Strong winds from the south continue blowing 20-40 mph gusting 50-60 mph, except in the Bridgers and near Cooke City where winds are a bit lighter. Temperatures are in the mid 20s F in most areas while in the Bridgers temperatures are in the low 30s F.
Today a deep trough will move across California and Nevada with our forecast area on the front edge of this system. The Centennial Range near Island Park will take the brunt of the storm with heavy snowfall and strong south winds continuing to gust 50-60 mph. By afternoon, winds will decrease significantly and precipitation should finally reach the Bozeman area. Temperatures will remain steady this morning before dropping late today when a cold front arrives.
Snow totals by tomorrow morning should be: 12-18” near Island Park, 6-12” near West Yellowstone, 6-8” near Big Sky, 4-6” near Bozeman and Cooke City. Lighter snowfall will continue tomorrow with a break this weekend before the next system brings snow and strong winds Sunday-Tuesday followed by even more snow later in the week.
Strong winds from the south will whip around the new snow forming fresh WIND SLABS that will be easy to trigger. They will start small and easily become a foot deep by midday near ridgelines exposed to the wind.
The new snow will be mostly right-side up but periods of heavier snowfall may create subtle layers in the new snow causing soft STORM SLAB AVALANCHES on slopes sheltered from the wind. Clues that storm slabs are becoming a problem include: snow amounts approaching a foot, heavy snowfall rates, and cracking in the new snow.
Near West Yellowstone a weak layer of facets buried 2-3 ft deep has been dormant. These probably won’t be an issue today, but could wake up in coming days and cause persistent slab avalanches as new snow stacks up. The last of these slides occurred about two weeks ago.
Today with wind and periods of heavy snow the danger will be rising to CONSIDERABLE on wind loaded slopes. The danger on non-wind loaded slopes will rise to MODERATE.
In areas closer to Big Sky, snow has already started, and strong south winds will be forming shallow wind slabs. In areas further north, not much snow may fall until after winds start dying down and there will be minimal wind slab formation.
Today the avalanche danger is MODERATE. Look for and avoid fresh wind slabs and drifts.
Upcoming Avalanche Education and Events
Avalanche awareness focused on springtime avalanche conditions: TODAY, March 13 at the Bozeman REI from 6-7:30 p.m. The event is free but has limited space and requires registration HERE.