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Issued
Fri, February 7th, 2020 - 7:00AM
Expires
Sat, February 8th, 2020 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger remains CONSIDERABLE above 1,000′. Triggering a large and dangerous slab avalanche 2-3′ thick remains likely and these avalanche could be triggered remotely. Natural avalanches are possible. Continued cautious route-finding and conservative decision making are essential today. Pay attention to changing conditions as the next storm moves into the area.

Below 1000′: Watch for precipitation falling as rain. If we receive more than forecasted we may see wet loose avalanches in this elevation band that could run to valley bottom in places like Byron Glacier.

*Roof Avalanches:  Warming temperatures are causing roofs to begin to shed their snow. Pay attention to children, pets and where you park your car. Rain will also increase this hazard.

Special Announcements

Do you have your Snowball ticket??? For the Love of Snow, Let’s Dance! Valentine’s Day – February 14, 2020. 7-11 pm at 49th State Brewing Co. in Anchorage. I Like Robots will be rockin’ our favorite 80’s tunes! Awesome silent auction and costume contest, so break out your best 80’s fashion and snow gear! $35 tickets on sale at www.AlaskaAvalanche.org/events/snowball. Bring your sweethearts, bring your buddies, or find new ones on the dance floor… Proceeds support Friends of the Chugach Avalanche Center and the Alaska Avalanche School.

Fri, February 7th, 2020
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. 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

Yesterday was a day for natural avalanche observations. A natural avalanche was observed in Crow Creek just after 2 pm. Details are unknown but the photo of the power cloud in action is concerning. A very large avalanche that was thought to have been naturally triggered sometime in the last couple days above Luebner Lake was observed from the air. This was the largest avalanche we know of recently.  In addition, a few natural avalanches were observed in motion out of the forecast area near Moose Pass and Cooper Landing. Over the past few days we know of 6 skier and/or snowmachine triggered slab avalanches from Girdwood, Turnagain Pass and Summit Lake. No one has been caught to date and several have been triggered remotely. All of these avalanches are failing on weak faceted snow 2-3′ below the surface. Many are being triggered in the mid-elevation band around 2,000′ and outside of wind effect. All of this data is pointing to a dangerous snowpack! Heads up!!!!

Powder cloud observed in Crow Creek just after 2 pm yesterday, 2.6.20. Believed to be naturally triggered. Details of avalanche are unknown at this point.

Crown observed from the air yesterday above Luebner Lake. The date the avalanche occurred is unknown but thought to have been in the past couple days and naturally triggered. The total crown is approximately 2,000′ wide. 2.6.20. Photo: Henry Munter. 

 

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • 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.

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

Triggering a large dangerous avalanche on buried weak snow remains a concern today. You might be starting feel like the forecast is a broken record because we keep saying this and the danger is still CONSIDERABLE. Unfortunately signs continue to point to large avalanches being a very real and scary possibility and cautious travel has to be the prudent advice.  Wind loading in some terrain over the past week and warm temperatures have made the slab over the weak snow (facets and surface hoar) more connected. Often warm temperatures are associated with healing in the snowpack but this time it is actually making things worse. The slab is more cohesive and it’s increasing the potential size of the avalanche (example being the Luebner avalanche) and the likelihood of triggering an avalanche remotely (from the side, below or above a slope). There have been multiple human triggered avalanches reported this week and some concerning natural avalanches. There is snow and wind in the forecast today and tomorrow. These will add more slab and stress to the snowpack. The message today is again… Weak snow that formed in January is lurking 2-3′ below the surface. Please don’t be the trigger!

Some things to remember with this kind of avalanche problem:

    • Tracks on a slope do not make it safe. It could be the 2nd or 10th person that triggers the slab.
    • Remote triggering is possible. This means trigging a slide from below, the side or from on top.
    • Signs of instability may not be present before a slab releases.
    • Small slopes in the trees may avalanche.
    • Consider the consequences if the slope does slide. Is there a terrain trap you could be caught in?

Wind slabs: To add insult to injury… While you are trying to avoid large persistent slab avalanches also be on the lookout for fresh wind slabs in leeward terrain.

Weak snow under a slab on Seattle Ridge. 2.6.20.

Video link HERE.

Weather
Fri, February 7th, 2020

Yesterday: Mostly clear skies in the morning and then clouds building in the afternoon. Temperatures were in the 20Fs at upper elevations and the low 30Fs at lower elevations during the day and overnight. Winds were westerly 5-15 mph gusting into the 20s. Wind shifted to the east and increased overnight to 10-20 mph gusting into the 40s.

Today: Skies will be cloudy with snow likely and 3-6″ forecast. Below 1000′ may see mixed precipitation. Winds will be easterly 15-25 mph gusting into the 40s. Temperatures will be in the mid 20Fs to low 30Fs. Snow showers will continues overnight with another 3-6″ possible.

Tomorrow: Snow likely with rain at sea level. Temperatures in the mid 20Fs to mid 40Fs depending on elevation. Easterly winds through Turnagain arm could gust into the 60s. Temperatures cool slightly in the evening promoting more snow than rain showers and winds should decrease. There is overall cooling trend starting Sunday evening into next week.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28 1 0.1 54
Summit Lake (1400′) 23 0 0 20
Alyeska Mid (1700′) 27 1 0.02 55

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 NE 12 45
Seattle Ridge (2400′) 23 E* 7* 24*

*Big thanks to the Alaska Avalanche School motorized Level 1 class for cleaning off the Seattle Ridge anemometer (wind sensor) around noon yesterday! Wind data is from after that.

Observations
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Date Region Location
11/16/23 Turnagain Observation: Tincan Common
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11/14/23 Turnagain Observation: Seattle Ridge
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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.