20-21

Date

Thu, 12/31/2020 - 18:34

Activity

Skiing

Today Henry and I toured around Middle basin. We dug a pit on a NE slope at 9300’. There were 106cm on the ground. There were multiple faceted layers and two distinct crusts that appeared to be decomposing (see Henry’s snow pilot) Our layer of concern was a crust 30cm off the ground. CT24 SP @30cm, ECTX, PST44/100 (end) @30cm. Although lots of snow available for transport, we did not observe any wind slabs and winds remained calm to light throughout the morning despite obvious blowing snow on lone mountain.

Region

Northern Madison

Location (from list)

Middle Basin

Observer Name

Tatum

E fork hyalite, near Flanders

Date

Thu, 12/31/2020 - 12:15

Activity

Skiing

90 cm snow depth on E/NE aspect. Extended column test propagated at 40cm from the ground, ECT 10.
We dug around 9000 feet elevation.

Approx. 50 cm snow depth on north/ northwest facing slopes, around 8600 feet.

Region

Northern Gallatin

Location (from list)

NORTHERN GALLATIN RANGE

Observer Name

Emily Holmes

Flanders Mountain

Date

Thu, 12/31/2020 - 15:18

Activity

Skiing

I skied up Flanders today, and found conditions that are quite similar to my last visit a few days ago. A pit on an east aspect at 9100’ had HS 105 and gave ECTP15 just below a mid-pack crust that sits on ~25 cm of 4F angular facets. I did not experience any collapsing or cracking, and observed no recent activity. Despite the lack of obvious activity, the thought of skiing exposed terrain seems unpalatable to me.

This pit was 100-150’ below the one I dug on 12/28, and I did not find the well-defined pair of crusts that was present in that pit. I suspect being near some trees affected my results a few days ago. Nevertheless, the stability was poor in both pits, and the problem is the same—sugary, loose facets that cannot support much weight.

Region

Northern Gallatin

Observer Name

Sam Reinsel

GNFAC Avalanche Forecast for Thu Dec 31, 2020

Snowpack and Avalanche Discussion

It is snowing hard at Bridger Bowl as I write this at 6:30 a.m. Already 5” has fallen with a <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent </a>of .6”. The snow will stop this morning, but the winds will not. The Bridger Range has very weak snow which will avalanche naturally today. Stay clear of avalanche terrain. Expect to get whumpfs and cracks on the flats which could trigger avalanches on connected slopes. This is not a nuanced danger. For today the avalanche danger is rated HIGH on all wind-loaded slopes and CONSIDERABLE on all others. Triggering avalanches is likely and I urge folks to be conservative in their travels.

The snowpack south of Bozeman to Big Sky and West Yellowstone is weak. We have seen time and time again how just a little snow is enough to create unstable conditions. Two to 4” of snow is not much weight in a normal season on an average snowpack, and this year is neither. The foundation of our snowpack consists of weak, sugary snow that crumbles away. Winds are blowing this snow into drifts that will crack and likely avalanche. Expect to find these areas near ridgetops.

Collapses, or audible whumpfs, are an avalanche on flat terrain. It is when your weight fractured a weak layer that propagated some distance. Besides avalanches themselves, whumpfs are the next best sign that slopes are unstable. After a fresh load of snow I expect the snowpack will be “talking” to us, and we should listen to her warning.

Today, weak snow at the ground will be under stress on wind-loaded slopes, just as Ian and I saw on Buck Ridge (<a href="https://www.mtavalanche.com/node/23454">details…;) and Dave and I found at Lionhead (<a href="https://youtu.be/rWeNgK6_PTs">video</a>, <a href="https://www.mtavalanche.com/images/20/above-ski-hill-profile-27-dec"><s…;). For today, the avalanche danger is rated CONSIDERABLE on wind-loaded slopes since avalanches are likely and the instability is widespread. All other slopes have a MODERATE danger.

Cooke City has a 5 foot deep snowpack that does not have widespread weak layers, however, not every single slope is stable. Yesterday morning a snowmobiler triggered an avalanche on Crown Butte that broke 1-2 feet deep and 150 feet wide. No one was caught. Dave and Ian took <a href="https://www.mtavalanche.com/photos">pictures</a…; and made a <a href="https://youtu.be/UEY5A4YXibg">video</a> at the crown (more <a href="https://www.mtavalanche.com/node/23465">details…;). This avalanche was in the midst of a sea of snowmobile tracks on big slopes; an isolated, yet serious event. Fortunately, this slide is in full view on the way to Daisy Pass and both riders and skiers can recalibrate their plans since the potential of triggering avalanches is not obvious when we are surrounded by wall-to-wall tracks. These are times when we need to adhere to our basic safety protocols of traveling with a partner, only exposing one person at a time on slope and carrying rescue gear. In other words, always be prepared for the worst, especially when avalanches are unlikely. For today the avalanche danger is rated LOW on all slopes.