Good morning. This is Ian Hoyer with the Gallatin National Forest Avalanche Forecast on Friday, March 29th at 7:00 a.m. Today’s forecast is sponsored by Spark R&D and Klim. This forecast does not apply to operating ski areas.
There are 3-5” of new snow near Bozeman and Big Sky, with 7-10” of new snow around West Yellowstone, Island Park, and Cooke City. Strong winds yesterday have backed off and are now blowing 5-10 mph out of the west with 15-25 mph gusts. Light winds will continue today, shifting a bit more southwesterly. Temperatures are in the teens and 20s F this morning and will rise into the high 20s and 30s F. Expect a mix of sun and clouds through the day and a few snow showers, but no real accumulation.
Over the last 36 hours it has snowed 10-16” (1.1-2.0” of snow water equivalent). Strong winds yesterday drifted this new snow into slabs that will be easily triggered today. Either simply avoid these drifts or check to make sure they’re well bonded to the old snow surface before getting onto steeper slopes. Small, steep test slopes can be a great way to safely assess these surface instabilities (photo of a small windslab I triggered yesterday near Cooke City). Recent avalanches or shooting cracks are clear signs of unstable drifts that mean steep wind-loaded slopes are ready to avalanche.
These wind slabs could be several feet thick by themselves and plenty dangerous, but would also be a good trigger for huge avalanches breaking on the weak layers at the bottom of the somepack. It’s been a bit since we’ve last seen one of these slides breaking deeper, but the loading over the last week with yesterday’s additional snow on top makes us a bit nervous about the possibility today (Bacon Rind video). Assessing these deeper weak layers is much more difficult than assessing the surface instabilities. The best management strategy is picking slopes on the lower angled and smaller end of the spectrum with less obstacles or terrain traps beneath them.
If the sun pops through the clouds, loose wet avalanches will quickly become a concern and with plenty of new snow and crusts beneath it they could be good sized and run far.
Human triggered avalanches are LIKELY and the avalanche danger is CONSIDERABLE.
Our concerns are generally similar around Bozeman and Big Sky, but with less new snow wind drifts will be a bit thinner and triggering an avalanche is a bit less likely. On many slopes the wind drifts that formed yesterday will have bonded well to the old snow surface, but be on the lookout for thicker drifts and those that aren’t bonded as well. Be on your toes if the sun pops out as the new snow will quickly become wet and start to sluff on steep terrain. Keep your terrain choices in check as deeper slides also aren’t totally out of the question today.
Remember that even shallow avalanches can be dangerous in the wrong spot (especially above cliffs where just getting knocked off your feet could have big consequences).
The avalanche danger is MODERATE.
If you get out please submit an observation. It does not need to be technical. Did you see any avalanches? How much snow is on the ground? Was the wind moving snow? Simple observations are incredibly valuable. You can also contact us by email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).
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