Yesterday a big wind event impacted Southcentral Alaska and unfortunately Turnagain Pass was not spared. Large plumes of blowing snow were observed on most ridgetops as well as scouring, anti-tracks, wind sculpted snow. We received several reports of small natural wind slabs releasing on the SW face of Tincan yesterday and could see fresh debris in a Northern chute of Corn Biscuit. Numerous wind triggered avalanches occurred in Summit Lake area as well as a large avalanche on a Northern aspect near Silvertip Creek. (More on this below.) Active wind loading occurred on the SE face of Seattle Ridge, but on the other side of the road the wind direction was funneling through terrain from the South at times. Be aware of wind slabs on a variety of aspects due to unusual wind loading patterns and cross loading. Triggering a hard supportable wind slab will be possible and could step down to a deeper persistent layer and propagate along larger slopes. Identify smooth or pillow-shaped surfaces in steep terrain where triggering a wind slab could break above you, once committed to a slope. Supportable surfaces where the snow is hollow sounding should also be suspect.
Sunshine: If winds are calm today radiation from the sun could make wind slabs more reactive in steep terrain on Southerly aspects. Pay attention to surface snow melting or point releases near rocks in steep terrain. The sun can also add stress to cornices and make them easier to trigger.
Strong winds blowing snow onto a Southern aspect of Tincan yesterday, but wind loading was also observed on Northern aspects yesterday.
Winds loading the SE face of Seattle Ridge yesterday.
Triggering a large slab avalanche 2+ feet thick is possible due to several buried weak layers within our snowpack. Recent snow this week combined with strong winds have added stress to the snowpack. More potential exists in places with a shallow snowpack like the Southern end of Turnagain Pass and Summit Lake zone. This was evident yesterday during the wind event where numerous large avalanches released naturally near Silvertip Creek and in Summit Lake. In the heart of Turnagain Pass we have been tracking several weak layers buried 1-2 feet deep (facets and buried surface hoar) and both have been reactive in stability tests. The tricky part about this avalanche problem is that these slabs are hard and supportable and may be difficult to assess. Yesterday we investigated a human triggered slab avalanche on Tenderfoot (from Tuesday) where the slab was disguised as hard sastrugi. Obvious clues like “whumpfing” or shooting cracks may not be present before a slope releases. Assess the terrain for consequences and remember that the bigger the terrain the bigger the consequences.
Deep Persistent Slabs: Keep in mind that there are deeper persistent layers that could ‘wake up’ if you find the wrong spot above 3,000′ in the Alpine. At these high elevations, old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is also more pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass.
Two large natural avalanches observed yesterday on the ridge East of Silvertip Creek, NE slope
Facets over a rain crust have been showing propagation potential in the mid elevation zone. This pit was in the Center Ridge area yesterday. Photo by Nick D’Alessio
Clear skies and strong NW winds impacted Southcentral, Alaska yesterday. Seattle weather station recorded 30-50mph NW wind most of the day, while Sunburst station was more protected from this direction and recorded West winds in the 10-30mph range. Overnight NW winds decreased to Moderate. Temperatures in the upper elevations remained in the single digits F all day yesterday while lower elevations increased into the teens F’s during the day. No precipitation was recorded.
Today will start out with clear skies becoming cloudy this evening. Winds will continue to mellow out and become light from the NW. Temperatures may be inverted in some areas with single digits in valley bottoms and ridge tops in the teens F to low 20F’s. No precipitation is expected.
Into this weekend temperatures will gradually increase into the 20F’s at all elevations and there’s a chance for snow showers Saturday. Winds are expected to remain the light to moderate range.
*Center Ridge and Summit Lake weather stations are currently down and data after 1pm (2/28/18) is unavailable.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||*16||0||0||72|
|Summit Lake (1400′)||*14||0||0||30|
|Alyeska Mid (1700′)||13||0||0||62|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||11||NNW||22||62|
|01/26/20||Turnagain||Observation: Pastoral||Allen Dahl|
|01/26/20||Turnagain||Observation: Tincan trees and north side Tincan Ridge||Joe Kurtak, Anchorage Nordic Ski Patrol|
|01/25/20||Turnagain||Observation: Magnum||Ryan Van Luit Forecaster|
|01/25/20||Turnagain||Observation: Tincan||Eric Roberts/ Kakiko|
|01/25/20||Turnagain||Avalanche: Sunny Side of Seattle||Peter Wadsworth|
|01/23/20||Turnagain||Observation: TIncan||Eric Roberts|
|01/23/20||Turnagain||Observation: Goldpan||Allen Dahl|
|01/22/20||Turnagain||Observation: Sunburst||Adrian Beebee|
|01/22/20||Turnagain||Observation: Sunburst||Ryan Van Luit Forecaster|
|01/22/20||Turnagain||Observation: Seattle Ridge||W Wagner 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.