The avalanche danger is MODERATE above 1000′. It is possible a person can trigger an avalanche 1-3′ deep, with the snow from last week sitting on top of weak surfaces. We’ve seen this combination of a slab on top of a weak layer throughout the advisory area, so approach steep slopes with caution today. Be on the lookout for changing conditions as the next round of active weather moves in this afternoon. The danger is LOW below 1000′.
Tue, March 8th, 2022
Alpine
Above 2,500'
2 - Moderate
Treeline
1,000'-2,500'
2 - Moderate
Below Treeline
Below 1,000'
1 - Low
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
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.
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.
Avalanche Problem 1
Storm Slabs
Certain
Very Likely
Likely
Possible
Unlikely
Likelihood
Historic (D4-5)
Very Large (D3)
Large (D2)
Small (D1)
Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing
avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and
natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.
Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question.
Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to
hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are
relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure,
or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.
Here we are three days out from the last storm, and still concerned with how well the new snow is bonding to the old surfaces. This is because the latest storm buried a variety of weak surfaces including surface hoar, near-surface facets, and a crust. Unfortunately these weak surfaces are slow to heal, and we may be headed into persistent slab territory. Since the snow fell on Saturday, we’ve seen natural and human-triggered avalanches near Girdwood, Turnagain Pass, the Placer Valley, and the Lynx Creek area. Some of these have been quite large, and we’ve found surface hoar at the bed surface at every avalanche crown we’ve been able to visit- most recently at the crown of an avalanche above Main Bowl on Seattle Ridge that we looked at yesterday.
We’ve noticed some concerning patterns with the recent activity. There have been multiple avalanches where somebody triggered an avalanche after there were multiple sets of tracks on the slope. We’ve also gotten multiple reports of remotely triggered avalanches. As we move further out from the last major loading event, the weak layer is slowly becoming less reactive, but it is still possible to trigger an avalanche today.
This weak layer seems to be present at most places in our advisory area, but it isn’t everywhere. There have been quite a few people getting out into avalanche terrain without triggering an avalanche over the past few days. If you are trying to get into steep terrain today, be aware that you are taking on a fair amount of risk, and do your homework. Look out for the classic signs of unstable snow- shooting cracks, collapses, and fresh avalanche activity. Take the time to hop off your machine or step off the skin track and look for this weak layer. It is easily identified in a quick hand pit, and is only buried about a foot deep in most locations. If you notice any warning signs, or if you identify the weak layer, use that as a sign to back off your objective. If you feel confident in your snowpack assessment, cover your bases by only exposing one person at a time to avalanche terrain and watch your partners from safe spots. If you’d rather not roll the dice, you can avoid the risk by sticking to lower angle terrain.
Winds are expected to bump up slightly this afternoon as the next round of active weather approaches. Be on the lookout for changing conditions if the storm arrives sooner than expected, and stay tuned over the next couple days as the storm develops.
The buried surface hoar we are concerned with. This particular sample was the culprit from an avalanche at the top of Main Bowl on Seattle Ridge. 03.07.2022
Debris from a large avalanche in Warmup Bowl. That’s a person on a snowmachine on a bump just to the left of the debris pile along the shadow line for scale. 03.07.2022
Click here if the video from Seattle Ridge below does not load in your browser.
Weather
Tue, March 8th, 2022
Yesterday: Skies were partly cloudy with high temperatures in the upper 20’s to upper 30’s F. Winds were light at 5-15 mph out of the east with gusts of 20-30 mph. Temperatures got down to the mid 20’s overnight, with no precipitation in the past 24 hours.
Today: Cloud cover is increasing today as the next round of snow approaches tonight. Winds will pick up slightly, blowing 10-15 mph and gusting around 20 mph out of the east. High temperatures are looking to be in the mid 20’s to upper 30’s F, with lows dropping down to the upper teens to mid 20’s F. Light snow is expected to start around sunset tonight. No precipitation is expected during the day.
Tomorrow: Active weather returns tonight, with light snowfall throughout the area. Our forecast zone is looking to receive 1-2″ overnight tonight, with another 2-5″ tomorrow. Easterly winds will bump up a little bit more tomorrow, with sustained speeds of 15-25 mph and gusts around 25-35 mph. The rain level should stay down around 200-600′, with high temperatures in the mid 20’s to upper 30’s F.
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.
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