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Issued
Tue, February 8th, 2022 - 7:00AM
Expires
Wed, February 9th, 2022 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger has risen to CONSIDERABLE above 1,000′ due to 8-12+” of new snow and strong easterly winds. Avalanches composed of the new snow (storm slabs, wind slabs and sluffs) are all likely to be triggered by people and could release naturally. Cornice falls are also possible. Larger avalanches are expected in the Girdwood/Portage/Placer regions where the highest snowfall totals exist. Careful route-finding and conservative decision-making are essential for anyone going into the backcountry.

The danger is MODERATE below 1,000′ where smaller wet/moist snow avalanches could be triggered.

Roof Avalanches:  Warm temperatures and rain at sea level may cause roofs to shed.

Tue, February 8th, 2022
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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
  • Storm Slabs
    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.

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

The parade of storms continues across the forecast region. Beginning yesterday afternoon, the 4th system since February 1st moved in. Overnight, between 5-10″ of snow has fallen with ridgetop winds in the 30-40mph range and gusts in the 70’s. We can expect another 3-5″ through today with decreasing easterly winds (15-25mph). Temperatures have risen enough for rain to fall at sea level and the rain/snow line sits around 300′. After a brief lull this afternoon, the 5th weather system for February will ramp up tonight and extend through midday tomorrow.

With anywhere from 8-14″ of new snow by midday today, along with the strong winds, we can expect to see all the classic storm snow avalanche issues. These are storm slabs, wind slabs, sluffs, and cornice falls. Even though the storm will be tapering today, we still need to be on our guard.

Storm slabs:  In areas seeing over 8″ or so of new snow, watch for storm slabs. Warming temperatures during the storm likely caused denser snow to fall over lighter snow (an upside-down storm). In this case, storm slab avalanches will be fairly shallow, essentially the depth of the new snow. Additionally, small surface hoar was seen yesterday before the snowfall in the mid elevations. This can add to the tenderness of storm slabs.

Wind slabs:  We can pretty much bet on new sensitive wind slabs on wind loaded slopes predominantly in the Alpine. Slabs could be anywhere from 1-3′ thick depending on the amount of new snow/wind and easy to trigger. They may be lower on slopes than expected and in cross-loaded gullies due to the way the winds channel through terrain.

Loose snow avalanches (sluffs):  Dry sluffs in the new snow in the mid and high elevations are likely and wet sluffs in the lower elevations.

Cornices:  Once again, ridgelines are being impacted by strong winds and cornices continue to grow and break off. They are often the culprit for triggering fresh wind slabs below during periods of strong wind.

 

Graph of the winds during the past week at the Sunburst weather station (3,812 elevation). All wind events are from the east and except for Saturday, coincide with several inches of new snow. Note the pattern of the last three storms since last Tuesday and the stronger storm over us this morning.

 

To the south of Turnagian Pass and in Summit Lake, much less snow has fallen, but winds are likely affecting these areas as well. Here the snowpack is much shallower and weak layers surrounding crusts are buried in the top 2 feet of the pack. Keep in mind that new wind slabs that form could overload buried weak layers and create a larger avalanche.

Glide Avalanches:  We are watching this crack pictured below in one of the most popular zones at Turnagain Pass. Keep you eyes peeled for these in the days to come and let us know if you see any additional cracks.

Glide crack that sits near the common motorized up-track. Chugach NF Avalanche Center Intern Allen Dahl took this photo yesterday. The crack is slowly opening and we should limit any time under it and watch it closely if in the area. 2.7.22.

Weather
Tue, February 8th, 2022

Yesterday:  Clouds moved in yesterday afternoon along with increasing east winds and snowfall. Overnight there has been 5-8″ of snow with a rain/snow line around 500′. Ridgetop winds have been averaging 40mph with gusts into the 70’s. Temperatures rose to the mid 30’sF at sea level overnight and to the 20’s at ridgelines.

Today:  The storm will slowly taper off through today before another system hits tonight. Between 3-5″ of additional snow is possible with a rain/snow line dropping to sea level as slightly cooler air is pulled in. Ridgetop winds should back to the 15-25mph range before increasing to 30-40mph tonight.

Tomorrow:  Snowfall with moderate easterly winds look remain through most of Wednesday as this next system slowly moves out tomorrow. Around 4-8″ of additional snow could be seen (Tues night through Wed evening). A chance for some clearing skies and cooling temperatures may occur on Thursday.

 

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26 6 0.5 94
Summit Lake (1400′) 20 0 0 36
Alyeska Mid (1700′) 25 7 0.5 89

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 17 NE 32 73
Seattle Ridge (2400′) 20 SE 15 31
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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.