Good morning. This is Kevin Wright with the Chugach National Forest Avalanche Information Center on Saturday, March 17th at 7am. This will serve as 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).
Above treeline we still have a MODERATE avalanche danger with a couple different persistent weak layers causing problems. Several smaller skier triggered avalanches were reported yesterday. Below treeline, the danger is generally LOW, but pockets of MODERATE can be found on steeper rolls if problems like buried surface hoar and buried sun crusts are present. Shady and sheltered aspects will be the best bets for finding safe travel in the mountains today.
The last storm that brought more than 2 feet of new snow to Turnagain Pass is fading into the past. As recently as yesterday some stability problems were still being found. Two distinct issues have been identified – a buried sun crust and buried surface hoar. Both of these weak layers have caused avalanches in the last 2 days, and that possibility remains today.
Concern #1 – Buried Surface Hoar
We have a few reports of people triggering slabs on Thursday and Friday on a buried surface hoar layer. We investigated a small avalanche yesterday and positively identified the weak layer. It may be difficult to find the surface hoar grains, but this is most likely the culprit in areas that did not get a sun crust. Our test pits showed consistent moderate failure with a clean shear plane and the ability to propagate. Check photos and a description of our investigation here.
This problem seems to be found at middle elevations, up to about 3000 feet, on most aspects. The one aspect where we have not noticed much natural avalanche activity is North, so it may be less common on those slopes.
Concern #2 – Buried Sun Crust
Direct South facing slopes will have a new sun crust on the surface from the strong sun exposure yesterday. This will make riding on those slopes difficult. What you can’t see unless you dig, is that all the new storm snow is sitting on the old sun crust from last week. This crust has a weak layer underneath it, and may collapse under the additional weight of a person. During the storm this layer was very sensitive, causing remote triggered avalanche problems in some areas.
Concern #3 – Wet loose activity
Direct South faces may heat up enough in the late afternoon and evening to find some wet avalanche activity. This is dependent on warm temperatures and direct sun exposure. It’s probably a good idea to avoid those South facing slopes late in the day.
Backcountry travel can be done safely today, but some areas may be prudent to avoid. Direct South faces are probably not recommended for the sun crust problem. Steeper slopes (greater than 35 degrees) on all aspects should be approached with caution.
The most recent snowfall ended more than 48 hours ago. Yesterday was an intensely sunny day with warmer temperatures and very little wind.
For today, light snow showers are possible in the morning, bringing only limited snowfall and diminishing by the afternoon. Generally light wind, except near Whittier where a West wind to 50 mph is possible this morning.
CNFAIC Weather Page and the NWS forecast
Wendy will issue the next advisory Sunday morning. If you get out in the backcountry we want to know what you are seeing. Please send us your observations using the button at the top of this page or give us a call at 754-2369. Thanks and have a great day.