Good morning. This is Eric Knoff with the Gallatin National Forest Avalanche Advisory issued on Sunday, February 20, at 7:30 a.m. World Boards in cooperation with the Friends of the Avalanche Center, sponsors today’s advisory. This advisory does not apply to operating ski areas.
A closed Low over Wyoming has produced east winds throughout our advisory area limiting snow accumulations. Over the past 24 hours, 3-4 inches of low density snow has fallen in the southern ranges while a Tr-1” has fallen in the north. Temperatures are much colder in the mountains around Bozeman with Bridger Bowl recording the lowest temperature of -7 F. Conditions warm steadily farther south. West Yellowstone is the warm spot at 21 F while the mountains around Big Sky and Cooke City are recording temps around 10 F. Currently, winds are blowing out of the SSE at 5-15 mph and should gradually switch to more westerly flow by this afternoon. Today, temperatures will struggle into the single digits in the north and low 20s in the south. Another 2-3 inches will fall in the mountains around West Yellowstone and Cooke City while the north will pick up an inch or two.
The Madison and Gallatin Ranges, the Lionhead area near West Yellowstone, the mountains around Cooke City and the Washburn Range:
The primary issue today will be wind slabs that have been formed by strong winds over the past few days. Prior to this latest storm the dominating wind direction has been from the WSW, which loaded north and east facing slopes. Over the past 24 hours the winds have switched and are now blowing out of the SSE, loading slopes that were previously scoured. This will add a twist to snowpack and terrain assessment.
Soft slab avalanches near the ridgelines will be today’s primary avalanche concern. Without a widespread weak layer these slabs should not propagate far and will likely stay confined to the new snow. They will mainly be a problem in terrain where small slides have the potential to sweep a skier or rider over rocks, into trees, or into confined gullies amplifying the consequences of a small slide.
A secondary concern is that fresh wind slabs may be resting on older hard slabs that formed during very high winds a few weeks ago. Triggering a hard slab avalanche will be difficult, but the consequences will likely be severe. Detecting and avoiding large wind rolls and high probability trigger points such as mid-slope rock bands and steep, convex rolls will limit the chances of triggering a hard slab.
Today, fresh snow and wind will make human triggered avalanches likely on all wind loaded slopes and slopes steeper than 35 degrees where the avalanche danger is rated CONSIDERABLE. Slopes less than 35 degrees that have not received a wind load have a MODERATE avalanche danger.
The Bridger Range:
Without a widespread weak layer the main stability issue for the Bridger Range will be wind loaded slopes. With very little snow over the past few days new snow avalanches will likely be manageable in size. The biggest concern will be triggering an older hard slab, which will be possible on north and east facing slopes. A hard slab avalanche was responsible for a fatality on the west side of the Bridgers last Monday( photo1, photo2). Steer clear of large pillow like drifts, especially if the snow feels hollow or sounds like a drum. Above all, use good backcountry procedures and always think about the consequences of triggering an avalanche.
Today, human triggered avalanches are possible and the avalanche danger is rated MODERATE.
I will issue the next advisory tomorrow morning at 7:30 a.m. If you have any snowpack or avalanche observations, drop us a line at mtavalanche@gmail.com or call us at 587-6984.
Truman Avalanche Report
The report on the avalanche fatality from February 14th in Truman's Gulch on the west side of the Bridger Range is posted online. You can read it here: http://www.mtavalanche.com/accident/11/02/18
3rd Annual Montana Ale Works Fundraiser
Tuesday, March 1 at 6:00 p.m. in the Railcar at Ale Works in Bozeman
Cost: $25 to benefit the Friends of the Avalanche Center
Details: Chef Roth at Montana Ale Works is creating tapas style servings that will be paired with select beer from Lone Peak Brewery. More information HERE.
Upcoming Education
Saturday, February 19, West Yellowstone
The Friends of the Avalanche Center will offer a FREE Basic Avalanche Awareness Workshop at the Holiday Inn in West Yellowstone, MT. 7-8 p.m. (next to the bar) Topics include: terrain, mountain weather, snowpack, rescue procedures, and recent avalanches in local riding areas.