Girdwood area – Alyeska snow safety triggered a 2′ deep and 500′ wide avalanche at low elevation (~1600′) during avalanche mitigation operations. The avalanche was triggered by the fourth person on the slope and released down to the facet and Halloween crust interface that we have observed throughout the advisory area.
Avalanche on facets over Halloween crust with wide propagation between chair 4 and chair 6 at Alyeska. Avalanche was triggered during control work. Photo: Alyeska Ski Patrol 11.30.21
|Signal Word||Size (D scale)||Simple Descriptor|
|Small||1||Unlikely to bury a person|
|Large||2||Can bury a person|
|Very Large||3||Can destroy a house|
|Historic||4 & 5||Can destroy part or all of a village|
Weak faceted snow buried 2-3′ deep is our main avalanche concern. This type of avalanche can often lie dormant for days to weeks before getting the right combination of snow load and trigger to release. The recent avalanche at Alyeska yesterday is a reminder that persistent slabs can release on lower angle terrain than expected, propagate more widely than expected, and be stubborn to trigger, with the fourth skier on the slope having triggered the avalanche. Taking a conservative approach to selecting terrain (smaller terrain features, slope angles below 35 degrees), travelling one at a time in avalanche terrain, and spotting your partners is essential to manage this avalanche hazard. If you are travelling to one of the newly opened motorized areas (Placer, Skookum, Lynx, Johnson Pass, Lost Lake, ect) keep in mind that we have very limited information and recommend a conservative approach while we can start to visit more areas and get more public observations.
So far the new snow loads from the past 48 hours and during the week of Thanksgiving have not been enough to produce significant natural avalanches on these persistent weak layers. Instead they have incrementally loaded these weak layers to the point where the size of the avalanche that could be triggered has increased. Based on our exploration of the snowpack on Tincan yesterday, it seems like the weak layers are more prevalent below 3000′ where the Halloween melt freeze layer is thicker and a thicker layer of weak faceted snow remains from the cold spell in mid-November. Most of the avalanches reported in the advisory area in the past week have been at or below 3000′ (Seattle ridge, Girdwood, Tincan, Alyeska yesterday).
Digging a snowpit can be a good way to check on persistent weak layers in the area you are travelling. Keep in mind that snowpits only give you information about a single point and can vary greatly across a slope, so choosing a representative location is key. Stability tests can struggle to initiate a failure in deeply buried weak layers and can provide confusing results. The bigger value is just to understand the snowpack structure in your area and determine whether persistent weak layers are present and how sugary and soft they are.
Wind Slabs: In higher elevation areas, above 2500′, that saw the brunt of the winds from early yesterday morning it is still possible to trigger a wind slab. Look for firm and hollow feeling snow and signs of active wind transport. These are especially likely along ridgelines or in passes at higher elevations.
Snowpack structure from 3000′ on Tincan on 11.30.21. This area had more wind effect in the upper snowpack and a thinner layer of faceted snow that had smaller grain size and were stronger than what we saw at 2300′.
Glide activity has continued to decline and many of the lingering glide cracks are slowly getting filled in by the recent storms. They can still be a hazard to fall into and have to potential to spontaneously release. Minimize time underneath open glide cracks to avoid this unlikely but catastrophic avalanche hazard.
Yesterday: Cloud cover was in and out yesterday, with scattered snowfall but little accumulation. Temperatures were in the teens to mid-twenties. Winds were strong in the early morning hours, with gusts close to 40 mph on Sunburst, but calmed down to 5-10 mph with gusts to 15 mph for most of the day.
Today: The tail end of the storm could drop an additional 1-4″ of snow today with mostly cloudy conditions. Winds will range from 5-15 mph with gusts into the 20’s starting in the east in the morning and then switching to the northwest in the afternoon/evening. Temperatures will be in the teens and drop into the single digits this evening.
Tomorrow: Precipitation will taper off and temperatures will drop back into the positive and negative single digits. As the current low pressure moves out of the area we could see some increased winds, but the trend will be toward cold and calm again while we wait for the next storm system.
PRECIPITATION 24-hour data (6am – 6am)
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||25||0*||0*||68-70*|
|Summit Lake (1400′)||20||1||0.1||12|
|Alyeska Mid (1700′)||24||~6″*||0.4||N/A|
* Most snow depth and precipitation sensors area still giving errors in Center Ridge and Alyeska
RIDGETOP 24-hour data (6am – 6am)
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||21||E||2||7|
|05/17/22||Turnagain||Avalanche: Sunburst||CNFAIC Staff|
|05/17/22||Turnagain||Observation: Tincan Ridge||Joe Kurtak|
|05/11/22||Turnagain||Avalanche: Cornbiscuit and Magnum west faces||CNFAIC Staff Forecaster|
|05/07/22||Turnagain||Observation: Granddaddy||Kit Barton|
|04/29/22||Turnagain||Observation: Sunburst wx station||AS/ MM/ AM/ NH|
|04/28/22||Turnagain||Observation: More Turnagain Pass/Summit Lake wet slab activity||Alex Marienthal|
|04/27/22||Turnagain||Observation: Magnum||Sykes / Buttrick Forecaster|
|04/27/22||Turnagain||Observation: Girdwood/Summit/Turnagain Road obs||A S|
|04/24/22||Turnagain||Avalanche: Seattle Ridge – large glide avalanche on Repeat Offender path||CNFAIC Staff Forecaster|
|04/24/22||Turnagain||Avalanche: Seattle Ridge uptrack||Martin Schmidt|
Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: firstname.lastname@example.org
|Area||Status||Weather & Riding Conditions|
This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.