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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, February 26th, 2023 - 7:00AM
Expires
Mon, February 27th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains CONSIDERABLE in the upper elevations where winds continue to blow snow into drifts and slabs. Human triggered wind slab avalanches are likely on slopes that have, or are being, wind loaded. The danger is MODERATE on slopes out of the wind. Here there is still a chance of triggering a slab around 1-2+’ deep due to various questionable layers in the top of the snowpack. Additionally, sluffs are likely to be triggered in steep terrain and give cornices a wide berth. The danger is LOW below 1,000′.

SUMMIT LAKE:  Even stronger NW winds are impacting this region. Wind slab avalanches will be likely (both natural and human triggered) as well as the potential for a slab to break in deeper buried weak layers. This region has a weak and shallow snowpack, making avalanches more likely.

LOST LAKE / SNUG HARBOR:  This region is also seeing significant NW winds. Both natural and human triggered wind slabs could occur today.

Special Announcements

Turnagain Pass Avalanche Awareness Day – 2023:  Mark your calendars for Saturday, March 18th, and swing by on your way to or from your backcountry ride or ski!! Test your beacon skills, chow down on hot dogs, and bring your questions. The Alaska Avalanche School will be there along with a chance to demo snowmachines from Alaska Mining and Diving Supply and Anchorage Yamaha and Polaris. More details HERE!

Supporting local avalanche programs:  Thank you, Ira Edwards, for all your work raising funds for avalanche organizations in AK! For years Ira has organized the annual October Matchstick Productions ski film that benefits the Chugach National Forest Avy Center as well as the Alaska Avalanche School. Great job with this segment, Indie Alaska! If you haven’t seen it yet, check it out HERE.

Sun, February 26th, 2023
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. 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.
Recent Avalanches

We heard of one snowboarder triggered avalanche yesterday. This was on the SW face of Magnum and pictured below. It was seen by a group further away and reported that the rider was caught but then able to ride out of the way. Although unknown, this was most likely a fresh wind slab avalanche. UPDATE at 8:50am – group involved sent in their report HERE. It was indeed a wind slab ~100′ wide, 6-12″ deep, and ran ~300′.

Skier triggered avalanche on the southerly aspect of Magnum. Note the skier on the bottom left. Photo taken from the saddle between Magnum and Cornbiscuit, 2.25.23.

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Aspect/Elevation
  • 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.

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.

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

It looks like one more day of NW outflow winds before things quiet down tomorrow. If you are headed out to enjoy the sunshine and the chilly temperatures, keep an eye on where the winds are blowing – as wind slab avalanches are the main concern. Slopes with recent wind loading will be much more dangerous than areas out of the wind. This NW flow direction can split around certain zones/ridges, blow from all kinds of directions in channeled terrain, and even miss some zones if we are lucky. This can happen for portions of Turnagain Pass. Hence, starting from your drive, be on the lookout for what the winds are doing.

Once in the snow, keep an eye out for where winds have drifted snow. Does the snow feel stiff, hollow, or drumlike? Are there cracks that shoot out from your skis/board/machine? All these are clues you’ve found a wind slab and if the slope is steep enough it could slide. Wind slabs are likely to be in the foot deep range and touchy. That said, triggering a wind slab avalanche will be likely on freshly wind loaded slopes.

Cornices are also a concern. Giving them an extra wide berth is prudent. Remember, they can break further back than we might think.

Sun Effect:  With temperatures in the teens to single digits, the sun isn’t likely to heat those southerly aspects that are out of wind enough to create sun triggered sluffs or reactivate old weak layers. However, this idea should always be in the back of our minds this time of year.

Winds blowing southerly on the lower Tincan Ridge yesterday (terrain channeling as the main winds are NW along the higher peaks). Note the wind effect on the snow surface. Thanks to AK Guide Collective for the photo, 2.25.23.

Avalanche Problem 2
  • Persistent Slabs
    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.

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

In the top 2-3′ of the snowpack there are various layers of old buried surface hoar and small facets. Although we have not seen many avalanches break in these layers in general, the last one was a week ago in the Tincan Library. It’s still something we have on our radar. Triggering an avalanche in one of these layers is becoming unlikely, yet that does not mean there could be surprises out there. If we are hunting for areas sheltered from the wind today, this is a good reason to always pay close attention to any signs of instability (whumpfing/collapsing and cracking in the snow around you). It is also a good reason to always have good travel protocol, meaning exposing one person at a time, having escape routes planned, watching our partners, and having a plan if the slope does slide.

Additional Concern
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

In areas with a thinner snowpack there are weak layers near the base of the snowpack that remain a concern. After getting information from the southern end of Turnagain Pass last week and in Lynx creek, it appears this deeper snowpack issue is mostly out of our forecast zone and in the Summit Lake area. Therefore, we’ll keep talking about it, but mainly in the Summit Lake section of the Bottom Line above.

Weather
Sun, February 26th, 2023

Yesterday:  Sunny and windy conditions were over the region yesterday. The northwesterly outflow winds along ridgelines were in the 15-30mph range with stronger gusts depending on location. Temperatures warmed into the 20’F in the afternoon then took a downturn and hit the single digits by last night.

Today:  Another sunny and windy day is on top. The northwest winds are forecast to again be 15-30mph with strong gusts along ridgelines. Temperatures are in the single digits this morning, except for the mid elevations where they are in the teens. Daytime warming should again bump the lower and mid elevations to near 20F.

Tomorrow:  Sunshine is expected tomorrow, Monday, with lighter northwest ridgetop winds (~10mph). Temperatures should still be chilly, save for what the sun is able to warm up midday. The next shot for snow is Tuesday into Wednesday as a storm is forecast to move it. Stay tuned.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 18 0 0 66
Summit Lake (1400′) 9 0 0 38
Alyeska Mid (1700′) 18 0 0 70
Bear Valley – Portage (132′) 24 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 6 NW 9 34
Seattle Ridge (2400′) 12 NW 12 30
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.