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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, November 22nd, 2021 - 7:00AM
Expires
Tue, November 23rd, 2021 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

A MODERATE avalanche danger remains above the treeline and in wind exposed areas at ~2500′ and above. It will be possible to trigger wind slabs about 6-12″ deep in steeper terrain. Look for isolated wind slabs in higher elevation terrain and near ridgelines by identifying wind texture on the snow surface and stiff snow over softer snow.  In areas protected from the wind, loose sugary snow at the surface will cause sluffing in steep terrain. Glide avalanches remain an issue and could release unexpectedly, so minimize your time underneath them.

A LOW danger exits below 2,500′ and in areas sheltered from recent winds.

Mon, November 22nd, 2021
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
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

No known avalanches reported yesterday

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • 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.
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

Wind slabs remain our main concern today, with the potential for isolated wind slabs over weak faceted snow or buried surface hoar (snowpack details). The distribution of wind affected snow is variable across the advisory area. Higher elevation areas have been impacted more by the recent winds and are more likely to have lingering wind slabs or breakable surface crust. Look for these lingering wind slabs near ridgelines or cross loaded gullies by identifying snow surface texture and pillows on loaded slopes.

Dry Loose Avalanches: At mid and lower elevations or in protected areas the winds have had minimal impact on the surface snow and conditions remain soft and loose with a faceted upper 12-16” of the snowpack. Keep an eye out for loose snow avalanches (aka sluffing) in the faceted surface snow on steep terrain features.

Example of wind texture on the snow surface indicating recent wind transport and potential for lingering wind slabs from the west face of Cornbiscuit on 11.21.21

Example of the breakable wind crust that has been reported near ridgelines and in wind affected areas throughout the region. This photo is from the Chugach Front Range, but simliar conditions exist in Turnagain Pass. Photo from Andy Moderow 11.20.21

 

Avalanche Problem 2
  • Glide Avalanches
    Glide Avalanches
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
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

Glide avalanches are still a cause for concern throughout the area. Compared to the glide activity earlier this fall they are less active, but we are still getting reports of glide releases, especially in mid and lower elevations below 3000’. The widespread distribution of glide cracks can make it tricky to know when you are travelling underneath them, so be aware when travelling to new areas if you can’t see what is above you. Manage your exposure to this hazard by minizing time underneath them.

Widespread glide cracks in PMS bowl on Magnum from 11.21.21. My partner and I were lucky to set a skin track that was not underneath these, but we couldn’t see them from our approach and didn’t realilze the hazard until we gained the ridge.

Weather
Mon, November 22nd, 2021

Yesterday: The precipitation that was forecast to arrive in our area on Sunday to Monday shifted towards the east and conditions remained cold and clear. Average wind speeds were in the single digits with gusts between 10-15 mph and variable wind direction across the advisory area. Temperatures were as cold as -20 at the road level in Johnson Pass and in the low single digits to zero at ridgetops.

Today: Conditions will remain cold today with mostly sunny skies in the morning and the possibility increasing clouds this afternoon. Temperatures are currently in the minus single digits at all elevations and should stay in the single digits today. We may see trace amounts of snow down to sea level this afternoon. Winds remain light today in the range of 5-10 mph with variable direction.

Tomorrow: Another wave of precipitation is moving into our area tonight through Wednesday with a chance of snow starting overnight. Temperatures will increase overnight and should be in the teens tomorrow. Precipitation is likely in the next few days with accumulations of 3-6”. There is a high level of uncertainty with precipitation amounts for this storm system. Winds will be 10-15 mph out of the east and southeast tomorrow with gusts into the 20s at ridgetops.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 1 0 0 41
Summit Lake (1400′) -10 0 0 10
Alyeska Mid (1700′) 3 0 0 38

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 2 WSW 7 16
Seattle Ridge (2400′) 0 N 4 8
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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