Good morning. This is Eric Knoff with the Gallatin National Forest Avalanche Advisory issued on Monday, March 12 at 7:30 a.m. Northern Lights Trading Company and Planet Natural, in partnership with the Friends of the Avalanche Center, sponsor today’s advisory. This advisory does not apply to operating ski areas.
Since early this morning a fast moving storm has dropped nine inches of snow in the Bridger Range, 2-3 inches in the northern Madison and Northern Gallatin Ranges and a trace to one inch elsewhere. Currently, mountain temperatures are in the teens around Big Sky and low to mid-twenties over the rest of our advisory area. Winds are blowing 15-30 mph out of the WSW with gusts reaching close to 40 mph. Today, temperatures will warm into the high 20s to low 30s F and winds will continue to blow 25-35 mph out of the WSW. Snow will end late this morning but skies will remain mostly cloudy through the day. A warm and dry pattern will settle in this afternoon and remain in place through tomorrow.
The Bridger Range:
The primary concern for the Bridger Range will be wind slabs. Nine inches of new snow combined with strong upper elevation winds will make slab development most prominent below the ridgelines. West/southwest winds will make slopes on the east half of the compass most susceptible to wind loading. Slabs triggered high on the slope have the ability to entrain large volumes of snow and run long distances.
A secondary concern will be avalanches breaking on deeper layers in the snowpack. Slides initiated within the storm snow have the potential to step down to faceted layers buried 2-3 feet deep. Steep, rocky terrain will be the most likely to produce deeper avalanches.
Today, human triggered avalanches are likely on wind loaded slopes which have a CONSIDERABLE avalanche danger. Non-wind loaded slopes have a MODERATE avalanche danger.
The northern Madison Range:
The northern Madison Range has the weakest snow in our forecast zone. Over the past week multiple natural and human triggered avalanches have been reported in this area (photo, photo). Yesterday, Doug and I went on the hunt for weak snow in the mountains around Big Sky. Doug and his partners explored the Big Sky sidecountry while my partner and I assessed conditions on Yellow Mountain (video). Although we were miles apart, we found very similar conditions with the weakest snow being on east and south facing slopes. We both got columns to propagate with medium force on the facet layer buried two feet deep and Doug also got a column to propagate on the depth hoar near the ground.
Although the northern Madison Range only received three inches of new snow, strong winds out of the west/southwest will be loading leeward slopes. Fresh wind slabs will likely be forming over a firm ice crust, which will provide a smooth surface for slides to run. Avalanches initiated in the new snow could step down to faceted layers buried deeper in the snowpack.
Today, new snow and strong winds will make human triggered avalanches likely on wind loaded slopes steeper than 35 degrees which have a CONSIDERABLE avalanche danger. All other slopes have a MODERATE avalanche danger.
The Southern Madison and Gallatin Ranges, the mountains around Cooke City and the Lionhead area near West Yellowstone:
Dust on crust, lipstick on a pig – however you look at it riding conditions will be highly variable today. As cloudy conditions and cooler temps replace the warm-dry weather of the past five days, our primary concern will continue to be the weak, faceted layer buried 2-3 feet deep.
On Saturday Mark and I rode in the Taylor Fork and found this layer to be reactive in stability tests (video). Although it was taking hard force to get this layer to fail, it continuously demonstrated its ability to propagate. We also know this layer exists in the Gallatin Range (photo), mountains around Cooke City (photo) and Lionhead area near West Yellowstone.
The most likely areas to trigger a slide today will be on unsupported terrain features such as steep rollovers or in steep rocky terrain where the snowpack is shallow.
Buried persistent weak layers will continue to make human triggered avalanches possible and the avalanche danger is rated MODERATE.
Doug 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.
Events/Education
Come to Bridger Bowl on Saturday, March 17th (St. Patrick’s Day) with telemark skis, AT skis, alpine skis, snowboards, split boards, or even snow blades. The theme is Snowpocalypse based on the wildly popular Mayan 2012 apocalypse. $30 gets you into the races, a pint glass, t-shirt, a good time, a raffle ticket, and food by Cafe Fresco. Pre-register at Mystery Ranch or Grizzly Ridge March 11-16. Visit http://pinheadclassic.com/ or the Pinhead Facebook page for more info.
1-hour Avalanche Awareness at REI, Bozeman
Tuesday, March 20 at 6:30 pm. Sign up for this FREE class here.