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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, February 2nd, 2022 - 7:00AM
Expires
Thu, February 3rd, 2022 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′. Strong east winds yesterday built fresh wind slabs 1-3′ deep at upper treeline and alpine elevations which will be possible for a person to trigger today. Look for signs of recent loading on the snow surface, hollow feeling snow, and pillowy wind deposits on leeward aspects to identify terrain features with wind slabs.

Below 1000′ the avalanche danger is LOW. A thick crust buried underneath a few inches of snow from yesterday will make slab avalanches unlikely.

Special Announcements
  • Forecaster Chat # 2: Join us virtually this Thursday evening, Feb. 3 from 6:00-7:30 p.m., for an interview with US Air Force Major Kevin Kelly of the Alaska Rescue Coordination Center. We’ll get his behind-the-scenes perspective of the role AKRCC plays in backcountry search and rescue missions, and try to share some tips on how to help facilitate an effective rescue should something go sideways in the backcountry. The virtual event is free, but registration is required. Click here for registration info and more details.
Wed, February 2nd, 2022
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
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.
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Today should be a lull between active weather systems with calm winds, temperatures in the teens to twenties, and hopefully improved visibility during the day. The primary avalanche problem is wind slabs 1-3′ deep that were formed during the period of high winds yesterday, which were out of the east averaging 15-30 mph and gusting up to 65 mph on upper ridgelines for a period of almost 24 hours. The fresh wind slabs were touchy at treeline yesterday and we got multiple shooting cracks and small wind loaded features to release within the freshly transported snow. Today they will have had some additional time to adjust but could still be reactive, especially in areas that saw a lot of wind loading yesterday like along upper elevation ridgelines or cross loaded gullies.

We recommend evaluating the terrain and snowpack carefully if you decide to venture into upper treeline and alpine areas today. Look for areas with hollow feeling snow, shooting cracks, and signs of wind loading on the snow surface to identify specific features harboring wind slabs.

There are a few deeper weak layers in the snowpack that could produce larger avalanches if the fresh loading from wind transport has made them more reactive. These include a freezing fog crust from 1/25, which is buried 1-3′ deep, and the New Years Crust. These layers were not reactive in our instability tests yesterday but some of them have produced avalanches during the past week (see ob here) and are worth considering and evaluating before stepping into avalanche terrain. Avalanches on deeper weak layers like the New Years Crust are unlikely but the potential still exists in areas with a shallow overall snowpack, such as the southern portion of Turnagain Pass and wind scoured areas (see ob here for an example of shallow, weak snowpack).

Cornices: High winds yesterday with lots of soft snow at the surface for transport likely added some fresh deposits to existing cornices. It is prudent to give cornices a wide berth when travelling along ridgelines and be aware of their potential to trigger avalanches on the slope below if they release.

Loose Snow Avalanches: In wind sheltered areas the little bit of new snow from yesterday and the existing soft snow on the surface was producing pretty fast running dry loose avalanches (sluffs) in steeper terrain. These will not be big enough to bury a person but could knock you off balance in steeper terrain.

Small shooting crack in a fresh wind deposit at treeline on Pete’s N yesterday. Photo 2.1.22

Hard to see, but this is a small fresh wind slab about a foot deep on a cross loaded ridgeline at treeline. Photo 2.1.22

Sunburst winds over the past 36 hours showing the sustained strong winds along ridgelines that built fresh wind slabs. Photo 2.2.22

 

 

Weather
Wed, February 2nd, 2022

Yesterday: A pulse of snowfall and high winds moved through the area yesterday depositing 1-4″ of snow. The winds were averaging 15-30 mph with gusts up to 65 mph on upper ridgelines for about 24 hours. Temperatures stayed in the teens to twenties.

Today: Winds have calmed back down today and should remain calm until tomorrow morning. No new snow is expected today. Temperatures should stay in the teens to twenties. We should see a break in the cloud cover during daylight hours today before another system moves into the area.

Tomorrow: Another storm similar to Tuesday will move through the area but with warmer temperatures causing snowline to move up to 200 – 700′. Strong winds in the 15-35 mph range will accompany light snowfall with a few inches of accumulation possible.

PRECIPITATION 24-hour data (6am – 6am)

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24 3 0.2 93
Summit Lake (1400′) 20 2 0.1 35
Alyeska Mid (1700′) 23 0 0 84

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 14 ENE 17 65
Seattle Ridge (2400′) 18 SE 13 34
Observations
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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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