GNFAC Avalanche Forecast for Wed Feb 17, 2016

Not the Current Forecast

Good morning. This is Doug Chabot with the Gallatin National Forest Avalanche Advisory issued on Wednesday, February 17, at 6:45 AM. Today’s advisory is sponsored by Mystery Ranch and Yellowstone Ski Tours. This advisory does not apply to operating ski areas.


Mountain Weather

Yesterday, westerly ridgetop winds lessened to 20-30 mph which is where they’ll remain today. This morning mountain temperatures are in the high 20s under mostly cloudy skies. A moist southwest flow will keep skies cloudy as mountain temperatures reach the low 30s. By morning West Yellowstone to Cooke City will have a couple inches of new snow. Tomorrow will be stormy and snowy, although precipitation might begin as rain.


Snowpack and Avalanche Discussion

Bridger Range   Madison Range   Gallatin Range  

Lionhead area near West Yellowstone   Cooke City

Winds have calmed from Monday’s gusts of 60 mph. Snow blew off exposed ridgelines yesterday, but the wind slabs are mostly unreactive. Warm temperatures are fostering good bonding and triggering them will be difficult.

Within the snowpack are layers of weaker snow that we continue to assess. Currently, the weakest one can be found in the southern Madison, southern Gallatin, Lionhead area and around Cooke City where a feathery layer of surface hoar was buried this weekend (photo). It is under 1-2’ of snow around Cooke City and 8-12” elsewhere (photo). Skiers triggered an avalanche on this layer on Monday north of Cooke City on Miller Ridge. It was triggered from a distance which indicates it was very unstable. It is not found on every slope, which makes it all the more insidious. On Sunday, I toured into Lionhead with my shovel blade in hand, quickly searching for it a few inches down. I found it on different aspects and made a video on what to look out for.

Other layers of concern are the depth hoar at the ground and thin layers of facets 2-3 feet under the surface. On Sunday, a snowmobiler up Taylor Fork triggered a small, steep slope with a thin snowpack. The slide broke at the ground on depth hoar (photo). This type of avalanche is indicative of today’s avalanche potential. It is still possible to trigger avalanches, but the instability is not widespread. Natural slides are not occurring and warning signs such as cracking and collapsing are rare events. The snowpack is harboring layers that are getting harder to trigger and the only way to determine their stability is by digging and testing. As the slide in Taylor Fork illustrates, steep slopes with a thinner snowpack are still a problem.

For today, buried weak layers are still under stress from last weekend’s snowfall and wind-loading. Avalanches are still possible and the danger is rated MODERATE.


Alex will issue the next advisory tomorrow morning by 7:30 a.m. If you have any snowpack or avalanche observations to share, drop us a line at mtavalanche@gmail.com or leave a message at 587-6984.


EVENTS and AVALANCHE EDUCATION

A complete calendar of classes can be found HERE.

West Yellowstone: Saturday, February 20, 7-8 p.m., 1-hr Avalanche Awareness for Snowmobilers at the Holiday Inn.

Bozeman: Wednesday, February 24, 6-7 p.m. 1-hr Avalanche Awareness, Roskie Hall, MSU.