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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, February 15th, 2023 - 7:00AM
Expires
Thu, February 16th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2,500′ and MODERATE below 2,500′. A fast moving storm deposited between 4-10″ of new snow with strong winds yesterday afternoon. Watch for easy to trigger wind slabs in the higher elevations. These slabs should be around 1-2′ deep. Additionally, there is a chance a larger avalanche could be triggered that breaks in older weak snow around 2+ feet deep. As always, give cornices an extra wide berth and sluffs could be large and run further than anticipated.

SUMMIT LAKE: The Summit Lake area saw strong easterly winds yesterday with only an inch of new snow. This area has a weak snowpack and wind slab avalanches are likely. These could step down into buried weak layers, causing a larger slide.

SEWARD/LOST LAKE: Strong winds have impacted the Lost Lake zone that also picked up several inches of new snow yesterday. See this report from a rider who triggered a wind slab on Monday.

Special Announcements

Chugach State Park:  Strong north and easterly winds were seen yesterday in the Anchorage Front Range. Heads up that wind slabs have likely formed with all the new snow that has fallen in the past week.

Snowball 2023:  A big thank you to all those who attended our Valentine’s fundraiser last night!!

Wed, February 15th, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
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.
Recent Avalanches

We did not hear of any avalanche activity yesterday during the stormy weather. On Monday folks were able to trigger large sluffs on steep slopes. The last slab avalanche was on Saturday when a skier triggered a slab around 2′ deep on a lower elevation rollover on Eddie’s Ridge.

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

The Valentine’s Day Storm headed out quicker than anticipated last night and left us with 4-10″ of new snow. The Girdwood, Portage, and Placer valleys were favored with closer to 10″ while Turnagain Pass picked up 4-6″. Ridgetop winds during the the snowfall were easterly in the 20’s mph with gusts near 60mph. The winds died off as well last night and today we are expecting low clouds, possibly some sun peaking through, and very light westerly winds.

The main avalanche concern will be the wind slabs that formed yesterday. These should be found near ridgelines, in cross-loaded gullies, and on rollovers in exposed areas. Wind slabs will hopefully be easy to suss out by watching for wind loaded areas, stiffer snow over softer snow, and hollow feeling snow. Cracks that shoot out from you are also a sign you’ve found a wind slab. Over the last week there has been light snow trickling in with some surface hoar forming here and there. This means wind slabs could be more ripe to trigger as they may take a bit longer to bond.

Storm Slabs:  In areas sheltered from the wind, look for how much new snow has fallen. In areas seeing up to 10″ of new snow we could trigger shallow storm slabs at all elevations that are composed of the new snow. In areas with less snow, storm slabs should not be an issue.

Cornices:  As skies clear and travel along ridgelines becomes easier, be sure give cornices a wide berth.

Loose snow avalanches:  Watch your sluff. There is a lot of soft surface snow out there and sluffs triggered on steep slopes could run much further and generate more volume than anticipated.

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

Under the new storm snow are various layers that could be potential problems that would create larger avalanches. These are a couple layers of surface hoar that formed on really light snow last week. They have not been a concern yet, but something we are watching. These layers would be in the top foot or so of the snowpack.

Next is an old storm interface from Feb 5/6 that sits around 2-2.5′ deep. This interface was responsible for our last slab avalanche (a skier-triggered avalanche on Eddie’s last Saturday). That storm buried a layer of low-density snow sitting on a crust up to about 2000′, and there may be some spotty surface hoar at that interface in some areas. There is still some uncertainty with this layer.

In addition to that 2/5 interface, we are still keeping the 1/10 buried surface hoar layer on the radar. This layer is becoming less and less likely to make avalanches, even though it’s quite east to see in snowpits.

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

For areas with a thinner snowpack (Silvertip, Summit Lake), the weak layers near the bottom of the snowpack are still a factor in our terrain choices. This includes the weak snow around the Thanksgiving crust, as well as faceted snow at the bottom of the snowpack. Luckily these layers do not seem to be a factor in our core advisory area, but they are still a concern around the periphery.

Weather
Wed, February 15th, 2023

Yesterday:  Stormy weather was over the region yesterday. Snowfall amounts were roughly 6-10″ in near Girdwood and Portage and 4-6″ at Turnagain Pass. Ridgetop winds were easterly in the 20’s mph with gusts in the 50’s to 60mph. Temperatures remained just cool enough for snow to sea level, around 30F at the lower elevations and in the teens along the higher peaks.

Today:  The storm moved out last night and low level clouds with a couple flurries may be seen today. Clearing skies are also possible. Ridgetop winds look to be clam to light from the west. Temperatures are cooling, in the 20’s F at sea level and in the teens along ridgetops.

Tomorrow:  Partly cloudy skies with light southerly winds is expected for tomorrow. Temperatures look to remain in the teens at most locations. The next shot for snow will be Thursday night into Friday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24 5 0.4 73
Summit Lake (1400′) 23 1 0.1 37
Alyeska Mid (1700′) 24 5 0.4 75
Bear Valley – Portage (132′) 30 8 0.8 –

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 16 ENE 23 55
Seattle Ridge (2400′) 20 SE 21 11
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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