Over the past two days we know of 6 skier and/or snowmachine triggered slab avalanches from Girdwood, Turnagain Pass and Summit Lake. They have all been around 2′ thick. One triggered yesterday in the upper Girdwood Valley was just over 3′ thick. No one has been caught to date and several have been triggered remotely. All of these are failing on weak faceted snow 2-3′ below the surface. Many are being triggered in the mid-elevation band around 2,000′ and outside of wind effect.
Slab avalanche triggered Tuesday, Feb 4th. This slide was triggered at the crown and below the common skin track when a skier veered below the track to perform a stability test. Photo taken the day after on 2.5.20 by Jennifer Dematteis.
Slab avalanche triggered by second person on the slope. This is an example of slabs that are releasing in mid-elevation terrain and in the trees. Location: Pete’s North. 2.4.20. Photo: Leif Mjos
|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|
Triggering a dangerous slab avalanche that is large enough to bury, injure and kill a person remains likely. These slabs continue to release the minute folks venture off the beaten track and especially into areas that were not heavily trafficed in January. There was a bump in westerly wind last night, which could create some small wind slab issues in isolated areas today, but the main concern still lies deeper in the pack.
That said, we can’t let the clearing skis today sway our decisions in the backcountry. We are dealing with an unstable snowpack in the lower/mid elevations as well as the upper. Widespread collapsing (whumpfing) and several recent avalanches are clues we can’t ignore. The problem is, various weak layers of facets and buried surface hoar sit between 2-3′ below the snow surface. The slab on top is composed of either wind packed snow (wind loaded slopes) or settling and condensing snow due to the very warm temperatures. Either way, the slab on top of the weak layer(s) is showing it’s prime to avalanche and all slopes are suspect.
Some things to remember with this kind of avalanche problem:
This pit from Eric Roberts around 2,500′ on Eddies shows a failure just over 2 feet below the surface on buried surface hoar. The failure near the top of the snowpack is a shallow wind slab. The deeper weakness is clearly the more concerning in our situation now.
Yesterday: Mostly cloudy skies were over the region yesterday. Temperatures were warm, in the mid 20’s°F along ridgetops and near 30°F in the mid and lower elevations. Ridgetop winds were light from the west (5mph) before picked up slightly overnight to the 10-15mph range.
Today: Mostly clear skies are forecast before another system pushes in tonight. Ridgetop winds should continue to blow from the west in the 10-15mph range before turning easterly tonight and increasing to the 15-25mph range. Temperatures are expected to stay in the mid-20’s°F with lower elevations bumping up to near 30°F during the day. Snowfall overnight could accumulate to 1-2″ by tomorrow morning.
Tomorrow: Cloudy skies, cooler temperatures and light snowfall is expected before a large storm system heads into the region Friday night and into Saturday.
PRECIPITATION 24-hour data (6am – 6am)
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||29||0||0||56|
|Summit Lake (1400′)||27||0||0||20|
|Alyeska Mid (1700′)||29||1||0.05||56|
RIDGETOP 24-hour data (6am – 6am)
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||26||*N/A||*N/A||*N/A|
*Rime is covering parts of the Seattle Ridge wind sensor.
|01/24/21||Turnagain||Observation: Triangle bowl||Cooper Street|
|01/23/21||Turnagain||Observation: Seattle Ridge||A Schauer Forecaster|
|01/23/21||Turnagain||Avalanche: Tincan Trees||Matti Silta|
|01/22/21||Turnagain||Observation: JOHNSON PASS||Anonymous|
|01/20/21||Turnagain||Observation: Sunburst||Johnston-Bloom / Roberts Forecaster|
|01/19/21||Turnagain||Avalanche: Cornbiscuit||Schauer/ Johnston-Bloom Forecaster|
|01/19/21||Turnagain||Avalanche: Sunburst and Tincan||CNFAIC Staff|
|01/19/21||Turnagain||Avalanche: Seattle Ridge||CNFAIC Staff|
|01/19/21||Turnagain||Avalanche: Tincan 2900′ SW aspect below Hippy Bowl.||Kris Marshall|
|01/18/21||Turnagain||Observation: Turnagain Pass Road Obs.||A Schauer Forecaster|
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.