A widespread large natural avalanche cycle occurred over the past three days due to very wet and stormy weather. Clouds parted just enough yesterday afternoon for a quick look around at some of the carnage. Although we have a few photos below, avalanche activity on much of the terrain in the region is still unknown. If you are out and see crowns or signs of recent avalanches, please pass on your photos to us! We are mapping the extent of the cycle as best we can.
Large slab avalanche on the Repeat Offender slide path on SE facing Seattle Ridge. This slab extended well over 1,000′ to the left of the photo and was estimated at 3-5′ thick. 2.20.20. Photo: Travis Smith
Several slabs that released on Eddies west and SW face. Image from the RWIS webcams. 2.20.20
Very large slabs seen from the Tesoro station in Girdwood on the backside of Seattle Ridge. 2.20.20.
The mountains received a heavy blow from Monday night until yesterday morning. The stormy weather has moved out and a weak system is moving over us today, bringing a few inches of snow and light to moderate east winds. With the cloud cover and lower visibility, the significance of the natural avalanche cycle may not be well understood. As you can see from the photos above, the mountains are littered with large crowns, ranging from 3′ to over 10′ thick in the Portage Valley. Countless avalanches occurred and the snowpack needs time to adjust.
Storm totals from mid-elevation stations since Monday night, February 17th:
Large avalanches composed of the 3-5 feet of new snow (wind slabs, storm slabs, cornices and sluffs) are all likely to be triggered and dangerous enough on their own. These avalanches could also ‘step down’ into the older weak layers below, creating a much larger slide (more on that below). Not only are steep wind loaded slopes dangerous, but everything in between and down to the small slopes in the trees out of the winds.
What to keep in mind if you are interested in headed into the backcountry:
Under all the new snow sits weak faceted snow from January. These weak layers are anywhere from 3-6+ feet below the surface. Much of the artillery and naturally triggered avalanches appear to have either stepped down or released from the get-go in these deeper weak layers. This is something we will be tracking as we take stock of the aftermath of the cycle. How likely it is a person could trigger these deeper layers is a big question and due to the sheer size of the potential avalanche, is not something worth testing right now.
Check out this video of rapid snowfall followed by quick settlement at Turnagain Pass’s RWIS station during the past 24-hours.
Yesterday: Stormy weather in the morning gave way to clearing skies and calm weather in the afternoon and through the overnight hours. Until around noon, heavy snowfall and strong easterly wind impacted the region. From 6am yesterday morning, Turnagain and Girdwood picked up an additional 9-10″ of new snow at mid-elevations. Ridgetop winds gusted into the 70’s at Sunburst before quieting down to the 5mph range from the east. Temperatures have remained near 20°F in the higher terrain and near 30°F at sea level.
Today: Cloudy skies and light snow showers are expected today as a trough of low pressure is swinging through from the west. Between 3-6″ of new snow is forecast with (.3-4″ water equivalent) by tomorrow morning. Ridgetop winds are light and variable this morning and should pick up this afternoon to 10-15mph from the east.
Tomorrow: Partly cloudy skies, light winds and a chance for a few flurries are on tap for Saturday. As the series of storms moves out of Southcentral and high pressure moves in, skies should begin to clear late Sunday and into Monday. At this time, ridgetop winds associated with the clearing skies look to remain light and northwesterly.
PRECIPITATION 24-hour data (6am – 6am)
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||29||9||0.7||83|
|Summit Lake (1400′)||25||0||0||29|
|Alyeska Mid (1700′)||30||10||0.9||94|
RIDGETOP 24-hour data (6am – 6am)
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||25||*N/A||*N/A||*N/A|
*Seattle Ridge wind sensor is rimed over and not reporting.
|02/20/20||Turnagain||Avalanche: Turnagain Pass – (Sunburst, Magnum, Cornbiscuit)||CNFAIC Staff Forecaster|
|02/20/20||Turnagain||Avalanche: Turnagain Pass – Seattle Ridge, Pyramid, Eddies||CNFAIC Staff Forecaster|
|02/20/20||Turnagain||Avalanche: Seattle Ridge – Repeat Offender slide path||CNFAIC Staff Forecaster|
|02/19/20||Turnagain||Avalanche: Tincan||H. Thamm / R. Van Luit Forecaster|
|02/18/20||Turnagain||Observation: Tin Can||Michael Sepp|
|02/17/20||Turnagain||Observation: Cornbiscuit||Fredrik Norrsell|
|02/16/20||Turnagain||Avalanche: Eddies, Sunburst, Cornbiscuit||Alaska Avalanche School L-2|
|02/16/20||Turnagain||Observation: Sunburst||Troy Tempel|
|02/16/20||Turnagain||Observation: Pete’s North||Allen Dahl|
|02/16/20||Turnagain||Avalanche: Sunburst||CNFAIC Staff|
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: email@example.com
|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.