Good morning. This is Mark Staples with the 145th and final Gallatin National Forest Avalanche Advisory of the season issued on Sunday, April 10, at 7:30 a.m. Thank you to the Friends of the Avalanche Center, the Big Sky, Bridger, Moonlight Basin, and Yellowstone Club ski patrols, Gallatin Snow Rangers, and everyone who has sent us an observation or made a contribution. The list is endless, and our advisories wouldn’t be possible without your help. This advisory does not apply to operating ski areas.
A few places received a trace of snow; otherwise, it seemed like spring was finally overtaking winter yesterday. This morning temperatures dropped into the mid to high teens F, and winds increased to 15-20 mph from the W with gusts up to 30 mph. At the Bridger Ridge winds were blowing 25-40 mph. Skies are cloudy this morning and may produce a dusting of snow, but drier air and ridge of high pressure will move over the area today possibly bringing more sunshine and fewer clouds than yesterday. Temperatures should rise into the mid 30s F or higher depending on cloud cover. Winds will blow 10-25 mph from the W with higher gusts at ridgetops.
The Bridger, Gallatin and Madison Ranges, the Lionhead area near West Yellowstone, the mountains around Cooke City and the Washburn Range:
Currently the snowpack is cold and dry with good, settled powder from this week’s storms. Yesterday, skiers in the backcountry south of Bridger Bowl triggered a few avalanches up to 1.5 ft deep but no one was reported caught. Likely places to trigger an avalanche today are steep areas near ridges or other terrain features that collect wind-blown snow. Fortunately most mountain ranges in the advisory area except for the Bridger Range experienced light winds during the last few days.
There are three things to watch today – slope aspect, stability within the new snow, and cornices:
- Aspect is easy but important in the spring when the sun appears. Wet snow avalanches are possible on southerly aspects especially near exposed rocks. Better powder can be found on northerly aspects, but these slopes shaded from the sun may harbor any lingering instabilities in the new snow.
- Bonding in the new snow happens fast this time of year. It is also much easier to assess than deep instabilities which are not an issue. I don’t expect the snowpack will produce obvious signs of instability. Instead, test small slopes, perform quick stability tests (1-2 minutes) in the upper 1-2 feet of the snowpack, and don’t trust fresh wind slabs.
- Cornices are huge right now. It’s hard to know when or where they will break.
Today, human triggered avalanches are possible on any slope with a wind load OR any slope steeper than 35 degrees where the avalanche danger is rated MODERATE. On less steep slopes without wind deposited snow, avalanches are unlikely and the avalanche danger is rated LOW. If significant warming occurs today on S facing slopes, the avalanche danger could rise this afternoon for wet snow avalanches.
End of Season
Doug, Eric and I would like to thank you for your interest, support, comments, and observations. You are the reason we are here. This week we’ll post a few things to keep in mind as we head into spring. Keep in touch, drop us a line at mtavalanche@gmail.com or call us at 587-6984. See you in the fall.