The avalanche danger is MODERATE above 2500′. A layer of sugary facets on the ground at upper elevations could produce avalanches 2-4′ deep, but the chances are decreasing since we have had no significant snowfall this week. Lingering wind slabs up to 1′ deep and dry loose avalanches (aka sluffs) are also possible in steeper terrain. Below 2500′ the avalanche danger is LOW.
Special Announcements
Forecaster Chat #1: Come join us at Alaska Mountaineering and Hiking on Thursday, December 15th for our first forecaster chat with John Sykes. Admission is free! Start time roughly 7pm, exact time TBD. The forecaster chat will focus on how to streamline submitting high quality observations and a discussion on decision-making in unusual conditions.
Sat, December 3rd, 2022
Alpine
Above 2,500'
2 - Moderate
Treeline
1,000'-2,500'
1 - Low
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.
Recent Avalanches
We saw a few small natural wind slabs yesterday on Magnum that probably released during the last wind event on 12.1.22. Otherwise the last observed avalanche activity were small natural wind slabs last weekend during the 11.25-26 outflow wind event.
Avalanche Problem 1
Persistent Slabs
Aspect/Elevation
Certain
Very Likely
Likely
Possible
Unlikely
Likelihood
Historic (D4-5)
Very Large (D3)
Large (D2)
Small (D1)
Size
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography.
This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects.
Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.
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.
The last known avalanche activity on the facet layer on the ground was back on 11.13.22, nearly three weeks ago. We are keeping it in the forecast due to uncertainty about the distribution and sensitivity of this layer at higher elevations. Our recent snowpit tests have shown a mixture of results, with some areas producing full propagation on this layer and other areas having no results. This is pretty typical for a deeply buried persistent weak layer. While we think it is unlikely for a person to trigger an avalanche 2-4′ deep on this layer today, we are still looking for more information from higher elevations (above 3000′) so please submit an observation if you get a chance to test this layer today!
There is also a possibility of finding a lingering wind slab up to 1′ deep today. The most recent round of wind slabs formed on 12.1.22 on top of a layer of near surface facets which can help them stay reactive longer than normal. These are most likely to be found in steep terrain along upper elevation ridgelines and cross loaded gullies. Keep an eye out for firm hollow feeling snow and shooting cracks to identify areas that could be holding onto a stubborn wind slab.
Finally, the clear skies this week have lead to faceting on the surface in areas protected from the wind which can lead to fast running loose snow avalanches (aka sluffs). If you are travelling in steeper terrain today be aware of your sluff because they can easily knock you off balance. We recommend always using safe travel practices to limit the exposure of your group to avalanche terrain. Travelling one at a time, spacing out, and always spotting your partners are critical to manage your avalanche risk even when it has been awhile since a recent snowfall event.
Mixture of soft snow and wind hardened snow in alpine elevations. Photo 12.2.22
Weather
Sat, December 3rd, 2022
Yesterday: A strong inversion was in place yesterday, with temperatures remaining in the single digits at the road elevation and reaching up to the low 30s at upper elevations. Winds were light, averaging 5-10 mph with gusts into the teens at upper elevations. High clouds moved into the area but the sun still shined through.
Today: Temperatures are getting downright balmy at upper elevations, as of 4am Sunburst weather station is reporting 35 F and Portage is reporting 2 F. That is one strong inversion! Temperatures at lower and mid elevations are expected to increase slightly later this afternoon, but the inversion should remain in place through the weekend. Winds will remain light with averages of 0-10 mph today. Some high level cloud cover is expected in the area today.
Tomorrow: Sunday looks like a repeat of Saturday except with clearer skies. A storm should to move into the area on Monday and provide us with a little refresh of snowfall on Monday afternoon and evening.
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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