Good morning. This is Graham Predeger with the Chugach National Forest Avalanche Information Center on Thursday, March 22nd 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).
There continues to be a MODERATE avalanche danger for the core advisory area today. Buried sun crusts/facet combinations and buried surface hoar have the potential to act as the weak layer in which an avalanche can initiate. Additionally, pay close attention to and avoid slopes on the south end of the compass late in the day as intense solar radiation can easily tip the balance between stable and unstable snow this time of year.
Several persistent weak layers have been buried over the last couple of weeks contributing to a poor structure in our upper snowpack. Test results over the last several days are hinting that our first buried surface hoar layer (24-30″ down) is gaining in strength but when disturbed, this layer is showing the potential to propagate with clean quality 1 shears. Additional persistent weak layers in our upper snowpack include buried sun crusts/ facet combinations and a more recent layer of surface hoar buried during Monday’s storm.
Concern #1 Buried Sun Crusts
These will be found on slopes with a southerly-tilt today (there are several in the top three feet of our snowpack). Faceting snow above and below these crusts proves an excellent weak layer for an avalanche to run on. There have been several skier-triggered avalanches in the last week where these crust/ facet combinations have been the culprit.
Concern #2 Loose sluff and wet slabs
North aspects will be holding dry, quality powder throughout the day. Sluffing was commonplace yesterday in steeper terrain (> 38 degrees) with loose snow traveling fast and far. South aspects however are a different story. The surface consists of a breakable crust with a few inches of powder on top. This will be some of the worst skiing and snowmachining today and the most dangerous as they continue to heat up throughout the day. It is imperative that travelers avoid these south-facing slopes late in the day, as this is when the slopes are ripe to avalanche.
Pay particularly close attention to clues that south-facing slopes are undergoing rapid warming. This may include roller-balls, point releases or sinking (boot penetration) when you step off your snowmachine or skis.
Concern #3 Buried surface hoar
It will take finding the sweet spot or a large load such as a snowmachine or cornice drop to trigger the deepest (approx. 24-30″ down) buried surface hoar layer today. If this layer is affected, it will likely propagate and have the potential to become a large and destructive avalanche. The more recent buried surface hoar layer (6-8″ down) doesn’t have a cohesive slab on top of it yet. Though buried intact, it won’t be a big issue for slab avalanches until we get anCNFAIC Staff significant wind or snow event to create that slab.
This will be the third day since the core advisory area has seen any significant snowfall or wind.
Today looks to be starting out significantly warmer than yesterday with valley temps at 18 degrees this morning (single digits 24hrs ago). We can expect anCNFAIC Staff day of stable weather today with partly sunny skies, light wind and temperatures to reach into the lower 30’s.
CNFAIC Weather Page and the NWS forecast
Chris will issue the next advisory Friday 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.