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Issued
Wed, February 9th, 2022 - 7:00AM
Expires
Thu, February 10th, 2022 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE on all aspects above 2,500′. Wind slab avalanches will be likely for people to trigger in the higher elevations due to the strong east winds overnight along with increasing westerly winds today. Wind slabs between 1 and 2+’ in depth may be found near ridgelines, on rollovers, and in cross-loaded gullies. At elevations below 2,500, it may still be possible to find and trigger a wind slab in exposed areas in the trees and a MODERATE danger exists. Additionally, cornices have grown and be sure to give them an extra wide berth.

The avalanche danger is LOW below 1,000′ where a few inches of new snow sit on the wet snow from yesterday, which is freezing, and triggering an avalanche is unlikely.

Wed, February 9th, 2022
Alpine
Above 2,500'
3 - Considerable
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. Dangerous avalanche conditions. 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.
Recent Avalanches

The only avalanche seen yesterday during a few short periods of good visibility was this large slab in the Placer Valley. It was near the toe of the Skookum Glacier on an upper elevation SW slope.

Natural slab avalanche on a SW aspect seen from the Placer Valley (the Skookum Valley is just to the looker’s right). 2.8.22.

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

After another round of snow and wind last night, a break in precipitation and clearing skies are forecast for later today and tomorrow. Last night Girdwood and Portage Valleys saw 4-8″ of low density snow while Turnagain Pass and the interior Kenai only squeaked out 1-2″. The ridgetop winds, however, remained strong in most areas, blowing 20-30mph with gusts to 50 from the east. Although the winds are decreasing this morning, they are slated to turn westerly and increase through today (15-25mph) and into tonight (30-40mph) with stronger gusts. All that said, wind slabs will be our main avalanche concern.

The wind effect above treeline in the new snow from Monday night was significant. Large drifts, scoured ridges and wind slabs that look to be in the 1-2+’ deep range covered much of the upper elevations, only to be exacerbated by last night’s winds. Even though we didn’t see much natural avalanche activity yesterday, we also didn’t see much terrain in general. Paying close attention to the basic Red Flags will be key for anyone getting out today. Those are:

  • Recent Avalanches – any signs of natural avalanches, including cornice falls?
  • Shooting cracks – is the snow cracking around you? Do the crack shoot out?
  • Collapsing (whumpfing) – Is the snowpack dropping under you (collapsing). One group had a wind slab collapse under them yesterday, but was not steep enough to slide.
  • Winds – are there slopes seeing new wind loading by today’s increase in westerly winds? This is from the opposite direction than the winds so far and could form new slabs on previously scoured areas.

Overall, it will be a good practice to be suspect of all new wind slabs and ease into terrain with a conservative mindset.

 

Wind effect at the top of Treeline on a SE face of Seattle Ridge, looking north. 2.8.22.

 

More wind effect, this is on the southerly aspect of Cornbiscuit. 2.8.22.

In areas and on slopes that escaped the wind, keep an eye out for how much storm snow fell in the past couple days. Are there any red flags that tell you it hasn’t fully bonded? Quick hand pits are good tools for this. Also, watch for sluffing in the new snow on the steeper slopes out of the wind.

Snowfall totals over the past 2 days:
–  Girdwood/Portage Valleys:  12-16″
–  Turnagain Pass:  6-12″ (more on the north end, less on the south)
–  Summit Lake:  1-2″

Cornices:  With the chance for skies to clear and travel along ridgelines doable, we have to give cornices an extra wide berth. These have changed shape and grown over the last couple weeks and could be teetering close to failure.

 

Weather
Wed, February 9th, 2022

Yesterday:  Stormy weather continued most of yesterday despite a brief break midday with some clearing skies. Snowfall over the past 24 hours was 1-2″ for Turnagain Pass and Summit Lake while Girdwood and Portage Valleys saw closer to 3-5″ (most of which occurred last night). Ridgetop winds have averaged in the 20-30mph range with gusts near 50mph from the east, these also were strongest overnight. Temperatures have cooled to the mid 20’s at sea level and the teens in the Alpine.

Today:  A break in weather is forecast today as the system over us moves out. After a few snow flurries this morning, there is a chance for some clearing skies. Ridgetop winds are expected to turn westerly and pick up into the 15-25mph range and increase into the 30’s later tonight. This will bring in colder air, dropping temperatures to the teens at most locations by this evening.

Tomorrow:  Mostly to partly cloudy skies are forecast with the chance for a few snow showers (only a trace of accumulation). The strong westerly winds along ridgelines should start backing off midday before turning easterly tomorrow night ahead of yet another pulse of wind and precipitation for Thursday night into Friday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30 1 0.1 92
Summit Lake (1400′) 26 1 0.1 36
Alyeska Mid (1700′) 27 7 0.6 93 (estimate)

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20 NE 24 50
Seattle Ridge (2400′) 22 SE 13 32
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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.