A cornice collapsed on Monday triggering an avalanche on the slope below. Photo: GNFAC
A cornice collapse in Sage Basin triggered an avalanche on a wind-loaded slope. The avalanche broke down to an old layer of buried surface hoar at 150 cm height (total snow height - 255 cm). The average depth is difficult to discern because the crown abuts the cornice line. The avalanche depth as stated was measured in the flank in a snowpit profile. Avalanche width and vertical run are estimated using photographs and Google Earth.
On 3/1/23 at 11am we saw a very large avalanche crown on the east side on Henderson Mtn., in the big avalanche path off the highest summit. It likely occurred late yesterday or early this morning. There was minimal new or drifted snow covering it, and it was snowing and blowing yesterday all day.
I estimate the crown is 6-8 feet deep, possibly 10 feet in spots. Measured on GoogleEarth to be 700 feet wide. 1200 feet vertical. HS-N-R3-D3-O. It did not go to the ground. Given how much wind-loading this path gets it may have been near the interface the 6 feet of snow that fell over the last 7-10 days, but it easily could have broken on a variety of faceted layers deeper in the snowpack.
Today wind was very calm and skies were partly cloudy. We saw a few shots of blue sky mixed with a few snow showers that totaled maybe 2-3cm.
On 3/1/23 at 11am we saw a very large avalanche crown on the east side on Henderson Mtn., in the big avalanche path off the highest summit. It likely occurred late yesterday or early this morning. There was minimal new or drifted snow covering it, and it was snowing and blowing yesterday all day. I estimate the crown is 6-8 feet deep, possibly 10 feet in spots. Measured on GoogleEarth to be 700 feet wide. 1200 feet vertical. HS-N-R3-D3-O. Photo: GNFAC
On 3/1/23 at 11am we saw a very large avalanche crown on the east side on Henderson Mtn., in the big avalanche path off the highest summit. It likely occurred late yesterday or early this morning. There was minimal new or drifted snow covering it, and it was snowing and blowing yesterday all day. I estimate the crown is 6-8 feet deep, possibly 10 feet in spots. Measured on GoogleEarth to be 700 feet wide. 1200 feet vertical. HS-N-R3-D3-O. Photo: GNFAC
On 3/1/23 at 11am we saw a very large avalanche crown on the east side on Henderson Mtn., in the big avalanche path off the highest summit. It likely occurred late yesterday or early this morning. There was minimal new or drifted snow covering it, and it was snowing and blowing yesterday all day. I estimate the crown is 6-8 feet deep, possibly 10 feet in spots. Measured on GoogleEarth to be 700 feet wide. 1200 feet vertical. HS-N-R3-D3-O. Photo: GNFAC
This morning at 11am we saw a very large avalanche crown on the east side on Henderson Mtn., in the big avalanche path off the highest summit. It likely occurred late yesterday or early this morning. There was minimal new or drifted snow covering it, and it was snowing and blowing yesterday all day.
I estimate the crown is 6-8 feet deep, possibly 10 feet in spots. Measured on GoogleEarth to be 700 feet wide. 1200 feet vertical. HS-N-R3-D3-O. It did not go to the ground. Given how much wind-loading this path gets it may have been near the interface the 6 feet of snow that fell over the last 7-10 days, but it easily could have broken on a variety of faceted layers deeper in the snowpack.
Today wind was very calm and skies were partly cloudy. We saw a few shots of blue sky mixed with a few snow showers that totaled maybe 2-3cm.
Pretty mild observations: north ridge above Hebgen, some woomfing on the ridge pretty subtle. This was yesterday morning, on the ridge top. Tons of new snow. Also point release in the slide area, north face of slide scare, above quake lake, visible from the road new in the last couple of days. Obviously natural trigger there.
Pretty mild observations: north ridge above Hebgen, some woomfing on the ridge pretty subtle. This was yesterday morning, on the ridge top. Tons of new snow. Also point release in the slide area, north face of slide scare, above quake lake, visible from the road new in the last couple of days. Obviously natural trigger there.
<p>In the last 24 hours, the mountains around West Yellowstone received 3” of snow, equal to 0.2” of <a href="https://www.mtavalanche.com/taxonomy/term/451"><span>snow water equivalent</span></a> (SWE). This is on top of nearly 3’ of snow that fell incrementally in the last eight days. Last night winds averaging 20-35 mph blew fresh snow into drifts where avalanches breaking several inches to a few feet deep are likely today. Yesterday, Doug and his partner rode at Lionhead and explicitly warned that the nice fluffy powder was primed to get blown into drifts sensitive to human triggers (<a href="https://www.youtube.com/watch?v=tyvsM8r40S4"><strong><span>video</span>…;). Identify and avoid wind-loaded slopes. Use environmental clues to predict which slopes were loaded by last night’s wind.</p>
<p><span>Dig and test for instability in and immediately below the recent snow (3’ deep) before riding in non-wind-loaded terrain. The avalanche danger is CONSIDERABLE on wind-loaded slopes and MODERATE on all others.</span></p>
<p>The mountains around Cooke City received 5” of new snow equal to 0.3” of SWE, and the winds are light. Near-constant snowfall since Friday has added up to two feet of fresh snow, and strong winds transported recent snow into thick drifts where triggering an avalanche is most likely (<a href="https://www.mtavalanche.com/weather/wx-avalanche-log"><strong><span>wea… and avalanche log</span></strong></a>). Since Saturday, four people have been caught and partially buried in avalanches; luckily, no one was injured (<a href="https://www.mtavalanche.com/node/28338"><strong><span>Town Hill - 2 partially buried</span></strong></a>, <a href="https://www.mtavalanche.com/node/28331"><strong><span>Mt. Abundance - partial burial</span></strong></a>, <a href="https://www.mtavalanche.com/images/23/skier-triggered-slide-near-round-… Lake - partial burial</span></strong></a>). Groups of riders and skiers reported many large, natural avalanches documented in our <a href="https://www.mtavalanche.com/avalanche-activity"><strong><span>Avalanche Activity Log</span></strong></a> (<a href="https://www.youtube.com/watch?v=8r-m6BAhr7E"><strong><span>Pilot Creek avalanche video</span></strong></a>). On Monday, Alex and I rode north of Cooke City and described our concerns, especially about wind-loaded slopes (<a href="https://www.youtube.com/watch?v=zg_5u0AZfNo&list=PLXu5151nmAvTi1DBS…;
<p><span>Be suspicious of commonly wind-loaded terrain, slopes with signs of recent wind-loading, and watch for signs of instability. Dig and test the upper three to four feet of the snowpack before engaging with avalanche terrain, whether wind-loaded or not. The avalanche danger is MODERATE. </span></p>
<p>The Bridger, Gallatin, and Madison Ranges received a trace to an inch of new snow in the last 24 hours. Our primary concern is avalanches breaking several inches to 2 feet deep below or within recent drifts or snow. Yesterday, a snowmobiler in Cabin Creek climbed a small slope, triggering an avalanche that broke 100’ wide and 20” deep (<a href="https://www.mtavalanche.com/node/28381"><strong><span>photos and details</span></strong></a>). Similar avalanches are possible today. Last Friday, a cornice collapsed in Bear Basin (<a href="https://www.mtavalanche.com/images/23/natural-cornice-collapse-beehive"… and details</span></strong></a>), and large, natural avalanches on <a href="https://www.mtavalanche.com/node/28360"><strong><span>Mount Bole</span></strong></a>, <a href="https://www.mtavalanche.com/images/23/large-natural-wind-slab-mt-blackm… Blackmore</span></strong></a> and <a href="https://www.mtavalanche.com/node/28325"><strong><span>Fan Mountain</span></strong></a> show us the larger end of the spectrum.</p>
<p>Heed warnings provided by signs of instability and test the upper few feet of the snowpack before considering steep slopes. Today, human-triggered avalanches are possible, and the danger is MODERATE.</p>
<p><span>Please share avalanche, snowpack or weather observations via our<a href="https://www.mtavalanche.com/node/add/snow_obs"><span> </span></a><a href="https://www.mtavalanche.com/node/add/snow_obs"><strong><span>website</s…;, email (<strong>mtavalanche@gmail.com</strong>), phone (406-587-6984), or Instagram (#gnfacobs). <span><span> </span></span><span> </span></span></p>
<p><span>Dangerous avalanche conditions exist on recently wind-loaded slopes. The Centennial Range received 16-20” of snow in the last three days, with more on the way. Winds gusted to 60 mph on <a href="https://www.mtavalanche.com/weather/stations/sawtelle-peak"><strong><sp… Peak</span></strong></a> last night before calming early this morning. Strong winds blew fresh snow into drifts where avalanches breaking several inches to a few feet deep are likely today. Predict which slopes were loaded by last night’s wind and avoid them. Dig and test for instability in and below the recent snow (3’ deep) before riding in non-wind-loaded terrain.</span></p>
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