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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, November 19th, 2023 - 7:00AM
Expires
Mon, November 20th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE above 1000′. Large human triggered avalanches are still possible at the high elevations, above 3000′. These could be 3-4′ deep and releasing near the ground. There is also evidence of a weak layer around a foot deep that could produce avalanches in areas without wind effect. In areas with wind loading, wind slabs up to a foot thick were triggered yesterday and could be triggered again today. Below 1000′, the avalanche danger is LOW.

Summit Lake: Similar avalanche conditions have been reported in the central Kenai mountains. Exercise caution especially when approaching high elevation terrain.

Special Announcements

Hatcher Pass – Conditions are quite dangerous right now, check hpavalache.org for more information!

Chugach State Park – Large avalanches that release near the ground at the higher elevations and fresh wind slabs are concerns for the front range as well. The new weekend avalanche outlook for the Chugach State Park will start Dec 1.

Danger Rating Outlook – This season we’re introducing an avalanche danger ‘outlook’ for the next day. This tool aims to help assess the danger trend and hopefully help plan your outings more effectively.

Sun, November 19th, 2023
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
Mon, November 20th, 2023
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
Mon, November 20th, 2023
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.
Recent Avalanches

Several smaller slab avalanches were triggered by skiers yesterday on Tincan and further back along the Magnum ridgeline in the Goldpan area. These were wind slabs 6-12″ deep and 10-20′ wide created by the northwest winds over the past couple days. The largest slab we know of was in Goldpan, reported to be 12″ deep and 50′ wide. This slab was triggered by the 5th person on the slope with no signs of wind effect present, which leads us to believe there is another weak layer to be watching for in the top of the snowpack.

If you look closely at the character of the crown in the above avalanche, it propagates further down slope on the flanks. This can point to the possibility of buried surface hoar or another weak layer may be at play. More on that in problem 1 below. Thank you to Sam Stark for the photo, 11.18.23.

 

Small photo of a small wind slab avalanche, one of several that were triggered on Tincan. 11.18.23.

Avalanche Problem 1
  • 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

Today is our second forecast of the season and already there are some avalanches to talk about. A big thanks to everyone that has written in about they have seen out there! It’s critical for us, especially as we gather as much intel as possible during the early season.

With another cold and clear day, our main concern remains a weak layer of faceted snow near the ground above 3000-3500′ in elevation. At these higher elevations there is still a chance someone could trigger a large avalanche, up to 3-4′ deep. Even though we have only seen one incident with this type of avalanche, it’s too big and unmanageable to forget about. We are suspect there could be another weak layer just a foot down or so. The avalanche pictured above from Goldpan yesterday could be pointing to this. We know there was a layer of surface hoar buried around a foot deep that hadn’t yet produced avalanches, but if this was the culprit here, it is a sign another weak layer is lurking and not easily identifiable.

Whether it’s the deeper weak layer or the one a foot deep, all these types of avalanches can be triggered remotely, meaning from the side, below, or on top of a slope. They can also release after several people have been on the slope without incident. Things to think about if you are headed to the high elevations today. As always, carefully assessing the snowpack near the ground and using conservative terrain selections will stack the odds in our favor.

 

Avalanche Problem 2
  • 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 more common, but much smaller, avalanche issue out there are wind slabs. These should be roughy a foot deep or less and may be more stubborn to trigger today as the northwest winds are on the decline before ramping back up tomorrow. That said, be on the lookout for wind deposited snow on leeward slopes. As a reminder, it’s typical for these northwest outflow winds to impact Seattle Ridge and areas along Turnagain Arm rather than the non-motorized side of Turnagain Pass. To identify wind-loaded areas, look for visual cues on the snow surface and ski or ride onto small test slopes to check for shooting cracks or small avalanches.

Wind effect in upper Lynx Ck Drainage, no reported signs of avalanches in this area south of Turnagain Pass. Thanks to Ivan Chikigak-Steadman for the photo! 11.18.23.

Additional Concern
  • Glide Avalanches
    Glide Avalanches
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.
More info at Avalanche.org

Heads up that a few glide cracks have released into avalanches. These have been seen in Girdwood valley as well as along Seattle Ridge. They have been relatively small pockets so far, but I’m guessing we’ll see more of these in the days ahead. They are unpredictable and the best way to avoid them is staying out from under glide cracks.

Glide avalanche that released Saturday afternoon (yesterday) on Raggedtop in the Girdwood Valley. 11.18.23.

 

Glide avalanche on Seattle Ridge, across from the motorized lot at Turnagain Pass. Andy Moderow 11.18.23.

Weather
Sun, November 19th, 2023

Yesterday:  Clear skies were over the region yesterday with chilly temperatures, teens and single digits. Winds were moderate to strong from the northwest along the ridgelines (15-20mph, gusting near 30).

Today:  Cold and clear sky conditions should prevail again today. Temperatures are sitting in the minus single digits in many locations this morning with Johnson Pass trailhead at -17F… The northwest winds should remain light to moderate again today (5-15mph range with some stronger gusts).

Tomorrow:  One more clear and cold day is slated for Monday. The northwest winds look to bump up as a stronger outflow is setting up in Southcentral as a whole.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 7 0 0 33
Summit Lake (1400′) 1 0 0 23
Alyeska Mid (1700′)
Bear Valley – Portage (132′) 20 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 3 W 10 22
Seattle Ridge (2400′) 9 NW 7 20
Observations
Recent Observations for Turnagain Pass
Date Region Location
02/24/24 Turnagain Observation: TinCan Backdoor/ Center Ridge
02/22/24 Turnagain Avalanche: Lynx Creek
02/22/24 Turnagain Observation: Turnagain, Seattle, Mt Ascension
02/21/24 Turnagain Observation: Tincan Trees
02/21/24 Turnagain Observation: Sunburst
02/20/24 Turnagain Avalanche: Tincan
02/20/24 Turnagain Observation: Seward Highway across from Johnson Pass TH
02/19/24 Turnagain Avalanche: Base of Seattle Ridge
02/18/24 Turnagain Observation: Lynx creek
02/18/24 Turnagain Observation: Tincan Trees
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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.