Archived Advisories

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Snowpack and Avalanche Discussion Attached images Attached Videos
Feb 24, 2017 - Eric Knoff
Madison Range  Southern Gallatin Range Lionhead area near West YellowstoneThe mountains around Big Sky and West Yellowstone have two distinct avalanche problems. The primary problem is wind loaded slopes. Earlier in the week, heavy snow and strong winds out of the W-SW produced widespread natural avalanches, mainly in the mountains near West Yellowstone (photo, photo, video). Winds have calmed over the past few days,...
Lionhead winds
Wind slabs avalanching on Lionhead Ridge
Falling tree triggered avalanche
Feb 23, 2017 - Eric Knoff
Southern Madison Range  Southern Gallatin Range  Cooke City Lionhead area near West YellowstoneWind loaded slopes are the main avalanche concern in the southern ranges. Earlier in the week, heavy snow and strong winds formed thick slabs on all aspects and elevations. On Tuesday, Doug and I rode in the Lionhead area near West Yellowstone and observed numerous natural avalanches in wind loaded terrain (photo,...
Lionhead winds
Wind slabs avalanching on Lionhead Ridge
Falling tree triggered avalanche
Avalanches and a HIGH danger in Lionhead
Feb 22, 2017 - Doug Chabot
Southern Madison Range Southern Gallatin Range Cooke City Lionhead area near West YellowstoneYesterday morning a few inches of snow fell in the southern mountains (.3-.5” SWE). Four-day storm totals show a settled depth of 2’ of heavy, dense snow measuring 2.5-3” of SWE, but snowfall is only part of the weather story, wind is the other. Gale force winds swirled from many directions and left little terrain...
Lionhead winds
Wind slabs avalanching on Lionhead Ridge
Falling tree triggered avalanche
Avalanches and a HIGH danger in Lionhead
Feb 21, 2017 - Doug Chabot
Southern Madison Range Southern Gallatin Range Cooke City Lionhead area near West YellowstoneA moist southwest flow has hammered the southern mountains. In the last 24 hours 1.3” of snow water equivalent (SWE) fell near West Yellowstone, Cooke City and Carrot Basin. This brings a 3-day storm total of 2.5” SWE (estimated to be 2’ of dense snow) to most areas. Besides snowfall, strong and gusty winds from the...
Pilot Creek Avalanche x2
Instability at Bacon Rind
Avalanche Debris, Mt Blackmore
Feb 20, 2017 - Alex Marienthal
Southern Madison Range   Southern Gallatin Range  Lionhead area near West Yellowstone The southern Madison Range and mountains near West Yellowstone got 3-5” of dense snow yesterday for a total of 1-1.5” of snow water equivalent (SWE) over two days. Southwest wind formed drifts of snow near ridgelines that will continue to grow today. These 1-3’ thick wind slabs are easy to trigger...
Avalanche Debris, Mt Blackmore
Not Perfect, But Not Bad - Bacon Rind
Feb 19, 2017 - Alex Marienthal
Southern Madison Range   Southern Gallatin Range  Lionhead area near West Yellowstone New snow in the southern Madison Range and mountains near West Yellowstone totaled .6 to 1.0” of snow water equivalent (SWE) since yesterday morning. Today it is easy to trigger avalanches in the new snow and wind slabs that formed from southwest wind.Fresh snow and wind slabs added weight to weak layers...
Avalanche Debris, Mt Blackmore
Daisy Pass Crown
Daisy Pass Avalanche Runout Zone
Not Perfect, But Not Bad - Bacon Rind
Feb 18, 2017 - Eric Knoff
Madison Range  Southern Gallatin Range  Lionhead area near West Yellowstone  Cooke CityA good freeze overnight will keep the snowpack locked up today on mid to low elevation slopes. This will eliminate the wet snow avalanche hazard. In upper elevation terrain, the snowpack still has lingering instabilities. In the mountains near Big Sky and West Yellowstone, a thin layer of facets buried 1.5-2...
Avalanche Debris, Mt Blackmore
Feb 17, 2017 - Eric Knoff
Cooke CityThe snowpack around Cooke City ranges from 6 to 10 feet deep. Persistent weak layers are not widespread and the pack has had time to adjust from the near record breaking snowstorm last week (photo page). Avalanche activity has been minimal the past few days; a clear indicator avalanches are becoming harder to trigger.While human triggered slides are less likely today, they are still possible. If a slide is triggered,...
Avalanche Debris, Mt Blackmore
Feb 16, 2017 - Eric Knoff
WET AVALANCHES: Above freezing temperatures and the potential for rain will increase the wet avalanche danger on steeper slopes. Pinwheels and point releases are signs instability. If these signs are present, move to lower angle terrain or to shadier aspects.Cooke CityIt has been five days since snow stopped falling around Cooke City. During this time, wind has been relatively calm and temperatures have been above average. This...
Sunlight Basin Avalanche, 2/14/2017
Daisy Pass Crown
Feb 15, 2017 - Doug Chabot
WET AVALANCHES: Above freezing temperatures will increase the wet avalanche danger on slopes getting full sunshine. Rolling pinwheels are a sign the snow surface is losing cohesion and wet-loose avalanches may occur.Cooke CityThe mountains around Cooke City are still adjusting to the huge snowstorm that ended late Friday. Over 11 feet of snow totaling 11” of snow water equivalent (SWE) fell. This was the third largest 14...
Sunlight Basin Avalanche, 2/14/2017
NRCS Fisher SNOTEL History
Daisy Pass Crown
Air bag deployed!
Feb 14, 2017 - Doug Chabot
Wet Avalanches: Above freezing temperatures will increase the wet avalanche danger on slopes getting full sunshine. Rolling pinwheels are a sign the snow surface is losing cohesion and wet-loose avalanches may occur.Cooke CityIf you Rip Van Winkled the last 2 weeks and missed the action in Cooke City, here’s a recap: it snowed a massive amount (11+ feet in 12 days), the winds blew and slopes avalanched bigger than anyone...
From the Air: Daisy Pass Avalanche
Air bag deployed!
Avalanche burial imminent
Henderson Avalanche Path
Feb 13, 2017 - Alex Marienthal
Cooke CityAn historic avalanche cycle took place in Cooke City after 8-10 feet of snow and strong winds last week. When skies cleared this weekend huge avalanches were visible, which ran historic distances, broke large trees, and deposited 20’ deep debris piles. Doug toured the carnage yesterday and posted a couple dozen photos and made a video to summarize the activity. See our photo page for a thorough tour of the...
Avalanche in Hyalite - 12 Feb
Large slab avalanche in Tepee Basin
Avalanches on Wolverine Peak
Henderson Runout Zone
Henderson Crown
Feb 12, 2017 - Alex Marienthal
Cooke City  Yesterday near Cooke City, skies cleared for the first time in over a week and the aftermath of an historic storm was visible (video). Large to historic sized avalanches were observed throughout the mountains on all aspects yesterday. Slides ranged from 1-3’ deep within the recent storm snow (photo, photo) to over 8 feet deep running historical distances (photo). Between Friday and Saturday morning a...
Avalanche on Mt. Hayden near Cooke
Explosive triggered deep slab avalanche at Big Sky
Avalanche in YNP from recent storm near Cooke 2
Asbestos Lake Avalanche
Damaged trees and debris across Lulu pass road from Henderson avalanche
Historic Avalanche on Henderson Mtn. over Lulu pass road
Feb 11, 2017 - Alex Marienthal
Cooke City  The mountains near Cooke City received historic snowfall over the last week with 8-10 feet of snow totaling 9.5” of snow water equivalent (SWE) over eight days. This storm was the largest since 1986 when 7.7” of SWE fell over six days. Snow stopped falling yesterday afternoon, but winds overnight continue to load slopes and form huge slabs of snow. Wind loading will continue today and large...
Explosive triggered avalanche on slope with shallow snowpack at Big Sky
Avalanche near Lulu Pass road 2, Cooke 10-Feb
Avalanche near Lulu Pass road, Cooke City 10-Feb
Avalanche near Sunlight Basin
Bostwick Canyon Avalanche
Feb 10, 2017 - Eric Knoff
Cooke CityCooke City is in uncharted territory. Over the past seven days, this area has received over 8” of SWE (snow water equivalent) totaling 5-7’ feet of snow. This breaks the seven day record set back in 1986. Yesterday, Alex and his partner dug a snowpit on a NE facing slope around 9,500 ft. and found a snowpack 10’ deep (video). He noted nearly 5’ was new snow over the past week. The pure weight of...
Avalanche near Sunlight Basin
Feb 9, 2017 - Eric Knoff
Cooke City  Over the past week, snowfall around Cooke City has been measure in feet! Fisher Creek Snotel site has recorded 6” of SWE (snow water equivalent) in the past 6 days. This is a tremendous amount of snow. Even the strongest snowpack will have difficulty supporting this extremely heavy load. Over the past five days, both natural and human triggered avalanches have been reported. This is bull’s eye...
Buried Surface Hoar, Deer Creek - 2/8/17
Natural Avalanches Cooke City, 2/8/17
Feb 8, 2017 - Doug Chabot
Cooke City  Cooke City got another 6+” of snow measuring .6” of SWE (snow water equivalent) totaling 5.6” of SWE since Friday, a hefty amount of weight. Winds were moderate yesterday, but today gusts of 40 mph will be loading many slopes. Widespread collapses (whumphs) were reported by a ski guide yesterday, and another skier had propagation in his stability tests 2’ under the surface. Steady...
Natural avalanche in Sheep Creek near Cooke - 2
Skier triggered avalanche on Town Hill in Cooke City
Skier triggered avalanche near Lulu Pass
Feb 7, 2017 - Doug Chabot
Southern Madison Range   Southern Gallatin Range   Lionhead area near West Yellowstone   Cooke City  The snow keeps falling in the southern mountains. Ten to 12” of new snow may not sound like a lot, but it was heavy (1.4-1.6” snow water equivalent) and part of a storm cycle that dropped 3.5-5” of SWE since late Friday. Oh yeah, and it’s blowing like crazy! On Sunday,...
Whiteboard thoughts
Natural avalanche in Sheep Creek near Cooke - 2
Skier triggered avalanche on Town Hill in Cooke City
Avalanche near Cooke City on Henderson Mtn.
Feb 6, 2017 - Alex Marienthal
Cooke City  Heavy snowfall and strong wind pushed the snowpack near Cooke City to its breaking point. Skiers in Sheep Creek yesterday reported a large natural avalanche that broke small trees, ran across flat terrain and up a small hill (photo, photo, photo). Skiers on Henderson bench triggered an avalanche that partially buried one skier (photo, photo). A skier on town hill triggered a slide, was caught and able to hug...
Toe of debris of natural avalanche in Sheep Creek near Cooke
Natural avalanche in Sheep Creek near Cooke
Skier triggered avalanche on Town Hill in Cooke City
Skier triggered avalanche near Lulu Pass
Feb 5, 2017 - Alex Marienthal
Cooke City  Southern Madison Range  Southern Gallatin RangeLionhead area near West YellowstoneThe mountains near Cooke City got almost 1.5” of snow water equivalent (SWE) since yesterday morning, in addition to .8” of SWE Friday night. The mountains near West Yellowstone and south of Big Sky received 1-1.5” of SWE since Friday. Strong wind out of the southwest has formed wind slabs 2-3’...
Wind Slab Formation in Middle Basin
Facets on an ice crust in Cooke City
Feb 4, 2017 - Eric Knoff
Cooke City  Southern Madison Range  Southern Gallatin RangeLionhead area near West YellowstoneThe southern ranges picked up a healthy shot of snow over the past 24 hours. Madison Plateau Snotel site near West Yellowstone is showing 8-10” of new snow totaling 1” of SWE (snow water equivalent). Fisher Creek Snotel near Cooke City is recording 6-8” of snow totaling .8” of SWE and Carrot Basin...
Facets on an ice crust in Cooke City
2 layers of surface hoar
Feb 3, 2017 - Eric Knoff
Cooke CityThe mountains around Cooke City picked up 3-5” of low density snow over the past 24 hours. This puts the four-day total at close to 3 feet. Light wind the past few days combined with a good bond between the new snow and old snow surface has kept avalanche activity to a minimum (video). This could all change as winds are forecasted to increase throughout the day.With an abundance of snow available for transport,...
Fresh wind slab - Cooke City
2 layers of surface hoar
Surface Hoar at Bacon Rind
Feb 2, 2017 - Eric Knoff
Cooke CityThe mountains around Cooke City picked up over two feet of snow Monday night and Tuesday. During the storm, heavy snow and strong winds added a rapid and heavy load to the snowpack (video). Fortunately, the new snow bonded well to the old snow surface and fell onto a relatively strong snowpack (video). Yesterday, my partner and I only observed one small natural avalanche on a wind loaded slope off Crown Butte (photo)....
Fresh wind slab - Cooke City
2 layers of surface hoar
Surface Hoar at Bacon Rind
Feb 1, 2017 - Doug Chabot
Bridger Range   Northern Madison Range   Northern Gallatin Range  The northern mountains from Big Sky to Bozeman got 10-12” of snow measuring .7-1” of snow water equivalent (SWE). Wind-loading was minimal and today’s concern is triggering avalanches at the old snow interface. Yesterday, a skier on Mount Ellis dug a pit and found a weak layer of surface hoar buried under the new...
2 layers of surface hoar
Surface Hoar at Bacon Rind
Rising Instability - Cooke City 1/31/2017
Jan 31, 2017 - Doug Chabot
Bridger Range   Madison Range   Gallatin Range   Lionhead area near West Yellowstone   Cooke City  It is snowing and blowing and the avalanche danger is rising. Wind and new snow will drift and avalanche. Today is a day to be mindful of the changing conditions. I recommend a cautious and conservative approach to backcountry travel since natural and human triggered avalanches are...
2 layers of surface hoar
Wind slab avalanche on Sage Peak
Wind Slab on Ernie Miller Ridge
Surface Hoar at Bacon Rind
Jan 30, 2017 - Alex Marienthal
Bridger Range   Madison Range   Gallatin Range   Cooke City  Lionhead area near West YellowstoneSnowfall followed by strong wind last week created 1-2 foot thick wind slabs that skiers and snowmobilers easily triggered a couple days ago (photo, video, photo). Recent strong wind has not had snow available to transport and grow slabs, and wind slabs have had time to stabilize. These...
Surface Hoar at Bacon Rind
Wind Slab in Hanging Valley at Big Sky
Snowmobile triggered wind slab near Cooke City
Jan 29, 2017 - Alex Marienthal
Bridger Range   Madison Range   Gallatin Range   Cooke City  Lionhead area near West YellowstoneWind slabs formed from strong west to northwest wind the past three days are possible to trigger today. The last two days, skiers and snowmobilers triggered 1-2 foot thick wind slabs in the Bridger Range (photo, photo, video), Northern Madison Range (photo), and Cooke City (photo). Minimal...
Wind Slab in Hanging Valley at Big Sky
Snowmobile triggered wind slab near Cooke City
Natural Avalanche in Northern Bridgers
Saddle Peak Soft Slab - 1/26/17
Jan 28, 2017 - Alex Marienthal
Bridger RangeStrong winds have drifted the 11” of snow that fell in the Bridger Range on Wednesday into slabs. These wind slabs formed over low density snow or weak facets and are easy to trigger today. Wind loaded slopes should be avoided. Doug and Eric went to the backcountry north of Bridger yesterday and found widespread cracking and collapsing of wind drifts, and triggered a small slide (video). Skiers in the...
Natural Avalanche in Northern Bridgers
Ainger Basin Profile - 27 Jan
Saddle Peak Soft Slab - 1/26/17
Jan 27, 2017 - Eric Knoff
Bridger RangeTwo factors play a key role in slab avalanche development - snow and wind. Today, the Bridger Range will have a surplus of both these factors. Fresh snow combined with strong gusty winds will make winds slabs the primary avalanche concern. Winds have blown mainly out of the W-NW, but given the downslope, swirly nature of winds in the Bridgers, I expect slopes on all aspects and elevations to have wind deposited snow...
Saddle Peak Soft Slab - 1/26/17