This is Mark Staples with the avalanche forecast for Thursday, December 26th, at 7:00 a.m. sponsored by Highline Partners and Gallatin County Sheriff Search and Rescue. This forecast does not apply to operating ski areas.
AVALANCHE WATCH
An AVALANCHE WATCH has been issued from 10 a.m. today until 5 a.m. Friday morning for the Island Park area, the Lionhead area, the southern Madison Range, and the southern Gallatin Range. Conditions are developing that will cause the avalanche danger to rise to HIGH by tomorrow. Heavy snowfall is expected to overload pre-existing weaknesses in the snowpack and create very dangerous avalanche conditions.
Recent snowfall - an extra inch of snow fell in most areas very early yesterday morning. It hasn’t been snowing a lot recently, but most areas south of Bozeman have picked up snow containing 0.5 inches of water over the last 7 days making the skiing and riding quite nice on slopes untouched by wind.
This morning snow is falling and ridgetop winds started increasing from the SW again at 20-30 mph gusting to 45 mostly at upper elevation ridgelines. Temperatures are in the upper teens and low 20s F. As of 6 a.m. only a trace to one inch had accumulated.
Today winds from the SW should continue to increase and blow all day. With cloudy skies and some snowfall, temperatures shouldn’t rise more than a few degrees. A heavy band of moisture rolling across the Snake River plain of Idaho will bring heavy snowfall to the Island Park area where the NWS has issued a Winter Storm Warning with 7-11 inches expected today. Most other areas to the north should get 2-4 inches today and a few more tonight.
Avalanche danger will be rising quickly in the mountains near Island Park that are in the bull’s eye for snowfall today through Monday. I was there just over a week ago, and we found a widespread weak layer of facets buried about a foot+ deep. Strong southerly winds and heavy snowfall today will make persistent slab avalanches 2 feet deep likey today. Slopes with wind drifted snow will be even more dangerous and avalanches could break even deeper. For these reasons the avalanche danger is CONSIDERABLE.
Now will be a great time to enjoy the snow, but take a step back today through next week. I would plan on riding in the trees on slopes less than 30 degrees in steepness that aren’t steep enough to slide. As snow accumulates, avoid being underneath all avalanche terrain and any steep slope.
In the mountains near West Yellowstone, Big Sky, Cooke City, and south of Bozeman, wind-loaded slopes from southwesterly winds on Tuesday and today will be the main concern. With a widespread layer of weak facets already buried 1-2 feet deep, the additional stress of a wind slab on top will make persistent slab avalanches likely on these slopes. Non-wind-loaded slopes have much less weight from new snow on them (aka stress), but with such a widespread weak layer, avalanches on these slopes remain possible.
Today the avalanche danger is CONSIDERABLE on wind-loaded slopes. The danger is MODERATE on all others. Regardless of the danger, consider stepping back and dialing down your terrain choices as we enter a period with more snow coming and rising danger. Avalanche conditions will be getting worse before they get better. Fortunately, new snow will make great powder for skiing and riding, and slopes less than 30 degrees in steepness will be the safest option.
The Bridger Range has simply received less snow than other areas and should receive less the next few days (although sometime around Sunday night looks promising). These mountains have a widespread weak layer as in most of the forecast area that is capable of producing avalanches especially in higher and more exposed terrain with more wind drifting
Persistent slab avalanches are the main concern mostly on wind-loaded slopes. Human-triggered avalanches are possible and the avalanche danger is MODERATE.
Upcoming Avalanche Education and Events
Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar
Monday, December 30, 6-8 p.m., Free Avalanche Awareness and Conditions Update, MAP Brewing.
We offer Avalanche Fundamentals with Field Session courses targeted towards non-motorized travelers in January and one geared towards motorized users. Sign up early before they fill up.
Every weekend in Cooke City: Friday at The Antlers at 7 p.m., Free Avalanche Awareness and Current Conditions talk, and Saturday from 10 a.m.-2 p.m. at Round Lake Warming Hut, Free Rescue Practice.
Friends of the Avalanche Center: Fall Fundraiser!
We’re still counting on your support and the online Fall Powder Blast fundraiser is 80% of the way to our goal. Please consider making even a small donation HERE or via Venmo