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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, November 23rd, 2022 - 7:00AM
Expires
Thu, November 24th, 2022 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′. New snow and winds will make it possible for a person to trigger a wind slab avalanche up to 1-2′ deep. The most dangerous locations will be at higher elevations near ridgelines, below convex rolls, and in cross-loaded gullies. There is also a weak layer of snow at the bottom of the snowpack that has the potential to make larger avalanches, especially at elevations above 3000′. The danger is LOW below 1000′.

Special Announcements

Turnagain Pass Motorized Use: The Chugach National Forest has issued a closure order for the Turnagain Pass motorized area due to inadequate snow cover to protect forest resources. Currently around 6-8″ of wet snow exists outside the motorized parking lot at the Pass. See the ‘Riding Areas’ tab below for the latest updates.

Avalanche Education Scholarships: Get your application in NOW! The Friends of the Chugach Avalanche Center hosts two different types of scholarships; the deadline is December 1st. Several opportunities are available. See details HERE. Help us spread the word!

New this season: we are adding the avalanche problem rose to our icons. We’ve posted a quick guide on how to use it (and its limitations) here.

Wed, November 23rd, 2022
Alpine
Above 2,500'
2 - Moderate
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.
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

We’ve received 3-5” snow since last night, with another 2-4” expected this morning before this pulse moves out later in the day. After an extended warm spell, we are finally seeing snow down at sea level again, with snow on the webcam out at Portage! Winds have been blowing 10-15 mph, gusting 20-25 mph out of the east since around midnight last night.

At higher elevations, there was already 6-10″ snow on the ground waiting to be blown into fresh wind slabs. Below around 2800′, this snow is burying a rain crust that had a light dusting of snow on it while we were out yesterday (details here). Be on the lookout for fresh wind slabs forming as light snow and moderate winds continue. These slabs will likely only be around 6-8″ thick in the mid and lower elevations, but could be 1-2′ thick at higher elevations. The most dangerous terrain will be below ridgelines, on the downhill side of convex rollovers, and in cross-loaded gullies. Look for generally safer conditions on slopes that are sheltered from the winds, and at lower elevations.

With 4-6″ new snow today and 6-10″ soft snow already on the ground yesterday, the wind will have plenty of slab-building material available. That layer of facets on the ground may still be an issue too- see problem 2 for more. 11.22.2022

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 addition to the surface problems mentioned above, we are keeping an eye on a layer of facets at the bottom of the snowpack. This layer formed in the snow that fell back in October, and has produced some large avalanches this season. The October facet layer has been giving mixed results in snowpits, showing cause for concern in some locations and looking just fine in others. It is early in the season, and we are still trying to figure out just how reactive this layer still is. Given the uncertainty with the layer and the size of the avalanches it is capable of producing, we’ve got to be careful choosing terrain. This layer appears to be most problematic at elevations above around 3000′ or so. If you are trying to get into the alpine, it will require doing some homework. Pay attention to any recent avalanche activity, and other warning signs like the whumpf of a collapsing weak layer, or shooting cracks. For a problem like this, with the little information we have on it at this point, it is worth taking a few minutes to dig down and see if there is weak snow at the ground before getting into steep avalanche terrain.

You can view yesterday’s video from Magnum Here if it doesn’t load in your browser.

Weather
Wed, November 23rd, 2022

Yesterday: Skies were mostly cloudy during the day with light easterly winds. Precipitation and winds picked up overnight, and as of 6:00 am, we have received 3-5″ snow, with the snow line dropping down to sea level for at least a portion of that. Winds have been blowing 10-15 mph out of the east with gusts of 20-30 mph since just after midnight. High temperatures were in the upper 20’s to mid 30’s F, with overnight lows in the upper 20’s to low 30’s F.

Today:  We should see another 2-4″ snow with easterly winds continuing at 10-15 and gusts of 20-30 before this system passes later in the day. The rain line may get back up to around 1000′ before precipitation wraps up. High temperatures will be in the upper 20’s to low 30’s F, with lows tonight dropping down to the high teens to low 20’s F.

Tomorrow: We should see a clearing between storm pulses tomorrow morning, with mostly sunny skies for at least part of the day and light easterly winds. There is a chance we could see clouds in the valleys during this time. Temperatures will be in the low to mid 20’s F during the day before creeping back up into the low 30’s tomorrow night as the next round of precipitation begins.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 3 0.3 20
Summit Lake (1400′) 30 2 0.2 11
Alyeska Mid (1700′) 32 5 0.6 20
Bear Valley- Portage (132′) 35 – 0.7 –

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25 ENE 10 30
Seattle Ridge (2400′) 28 ESE 9 16
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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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