|Travel Advice||Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.||Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.||Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential.||Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.||Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.|
|Likelihood of Avalanches||Natural and human-triggered avalanches unlikely.||Natural avalanches unlikely; human-triggered avalanches possible.||Natural avalanches possible; human-triggered avalanches likely.||Natural avalanches likely; human-triggered avalanches very likely.||Natural and human-triggered avalanches certain.|
|Avalanche Size and Distribution||Small avalanches in isolated areas or extreme terrain.||Small avalanches in specific areas; or large avalanches in isolated areas.||Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.||Large avalanches in many areas; or very large avalanches in specific areas.||Very large avalanches in many areas.|
We don’t have a lot of information about the high elevation deep slab because so few people have been traveling in the mountains over the last couple weeks. Yesterday on Seattle ridge we dug in a deeper area at 2900 feet and found 5 feet of mostly very strong snow on top of the old Nov/Dec persistent weak layers. (click on link for photos and pit profile) We could not get an extended column test to fail, but 2 compression tests revealed sudden collapse Q1 failures at the early December drizzle crust (CT24, CT21 Q1). The good news is that our recent wet storm has made some very strong snow – it’s difficult to cut through it with a sharp saw. I think it will be unlikely for a person to trigger the deep weak layers where the snowpack is in fact deep. It may be possible to trigger from shallow points where it could propagate to much deeper snow.
I’m still going to mention wet avalanches even though we now have a surface crust over everything. You have to dig through the crust to find the wet snow.
If someone were to trigger an avalanche below 3,000 feet, it will have some characteristics of a wet slab. Think about heavy, slow moving, bulldozer-like avalanches.
We dug a shallow pit just off the slope from the standard snowmachine up-track to Seattle ridge yesterday. Underneath the 4 inch think supportable crust is unbelievable weak, moist snow. Skis glide over the crust with no penetration, but trying to walk on it will sometimes punch a boot through the crust, which then drops through to the ground. It’s a very abnormal setup, and I’m honestly not sure how to measure its stability.
As more of the snowpack freezes up with the colder temperatures, strength will increase quickly and the possibility of triggering more avalanches in the wet snow will decrease dramatically.
Sunny breaks over the last few days will continue today. Southcentral Alaska is dominated by a blocking high pressure that is currently keeping clouds and storm from the west from entering our airspace. The big weather change that is affecting our snowpack is a drop in temperature. Ridgetop stations have been reading below freezing for over 48 hours. Lower elevation sites are now also freezing up. Wind is light and variable today.
Looking into the weekend – high pressure is expected to be the dominating feature for our region. Mostly clear skies are forecasted, with valley fog in some areas.
Graphs show the temperature profile at Center Ridge (1880 ft) and Sunburst (3812 ft). Blue line is 32 degrees (freezing).
|11/27/23||Turnagain||Avalanche: Tincan Ridge||Schauer/ Stiassny Forecaster|
|11/26/23||Turnagain||Observation: Road report: Slide with dirt on Repeat offender||Anonymous|
|11/26/23||Turnagain||Observation: Pete’s North||Ben Sullender|
|11/25/23||Turnagain||Observation: Tincan trees||John Sykes Forecaster|
|11/21/23||Observation: Spokane Creek||John Sykes Forecaster|
|11/19/23||Turnagain||Observation: Magnum – PMS Bowl||Schauer/ Cullen/ Jonas Forecaster|
|11/19/23||Other Regions||Observation: Sunnyside/Penguin||Jose Ramos-Leon|
|11/19/23||Turnagain||Observation: Eddies||Andy Moderow|