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Issued
Wed, January 18th, 2023 - 7:00AM
Expires
Thu, January 19th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains CONSIDERABLE above 1,000′. Triggering a 2′ deep slab avalanche is still likely, several occurred yesterday. Avalanches are breaking in buried surface hoar, being triggered remotely (from the side, top, or below), and releasing in treed areas and open areas. Increasing ridgetop winds today may create fresh wind slabs in the higher elevations. These also will be easy to trigger and could produce a larger avalanche below. Last, is the lingering possibility of triggering a very large avalanche on a weak layer buried 3-6′ deep.

The danger is MODERATE below 1,000′ in the event an avalanche occurring above sends debris into this zone.

*Cautious route finding and a conservative mindset is recommended, which means avoiding traveling on or below steep slopes.

Special Announcements

Forecaster Chat #2:  Join us at the Girdwood Brewing Co. from 5:30-7:00 p.m. tomorrow! CNFAIC forecaster Andrew Schauer will open the night with an overview of the state of the snowpack, followed by a discussion on how safe terrain management changes depending on the type of avalanche problem at hand. More details here.

Wed, January 18th, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
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

A lot of people triggered avalanches yesterday and so far we have not heard of anyone caught or hurt. Most of these were remotely triggered and all reported to be around 1.5 to 2′ deep. The weak layer is confirmed to be buried surface hoar (BSH) in a couple avalanches that were investigated and suspected in the others. Avalanches were releasing in the trees and on open slopes. Here is a list of known avalanches:
– Eddies (westerly facing roll):  One skier triggered slab, several recent naturals seen.
Tincan Trees:  Several slabs triggered in the trees, debris covering portion of an up-track
– Seattle Ridge (Widowmaker and SE side):  Four or more slabs triggered, many recent naturals
– Cornbiscuit/Magnum (Superbowl):  Recent natural slab avalanches observed

There was also a large avalanche that released overnight on Monday (two nights ago) that deposited debris onto the railroad tracks just a few miles SE of Girdwood. A northbound train ran into the debris and derailed. Two crew on board, no one hurt. Photos HERE and media report HERE.

 

Westerly roll on Eddies Ridge. Skier triggered with a ski cut. No one caught. Brady Deal, 1.17.23.

 

Example of many soft slabs that released in the Tincan Trees. Anonymous, 1.17.23.

 

Debris filling a terrain depression that an up-track often follows. Anonymous, 1.17.23.

 

Remotely triggered avalanches on Widowmaker from the ridge. Travis Smith, 1.17.23.

 


Debris from large natural avalanche near Kern Creek, covered railroad tracks, subsequent train derailment. Travis Smith, 1.17.23.

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

Triggering avalanches around 1.5 to 2 feet deep, similar to yesterday, will be likely again today. These are generally soft slabs that are releasing on a layer of surface hoar that was buried around a week ago (1/10 BSH). This is now becoming apersistent slab issue. As new snow piles up, the avalanches breaking on the layer will get bigger, as seen yesterday. Monday night’s snowfall exceeded expectations with 14-20″ at Turnagain Pass, hence slabs breaking around 2′ deep that were also composed of snow that trickled in over the last week. The storm headed in tonight could add another foot by tomorrow afternoon, creating larger slides if the storm verifies.

Adding to the issues in the top of snowpack, will be the possibility for wind slabs to develop today as ridgetop winds increase from the east. Winds are slated to start blowing hard enough to drift snow by noon. Wind slabs could overload the buried surface hoar, creating larger avalanches. Debris from a small wind slab could also trigger these 2′ deep slabs.

All in all, there are very touchy avalanche conditions currently and we haven’t even gotten to the issues at the base of the snowpack. More on that in Problem #2. Traveling in the mountains will require very careful terrain management. Even in treed areas we need to be on our guard. Small slopes can create enough debris to fill in depressions (as seen in the portion of the Tincan connector trail that was covered yesterday, photo above). Knowing we could trigger avalanches from a distance, from below a slope, or potentially threaten another group below, are all reasons to stick to mellow terrain.

 

A series of slabs triggered by a rider yesterday above the Widowmaker slide path on the backside of Seattle Ridge. Rider did not know these were triggered at the time of release. Photo by Travis Smith, 1.17.23.

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.

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

At elevations above around 2,500′ triggering a really big avalanche that breaks near the ground is still a concern. The weak layer with this problem is that Thanksgiving crust/facet combo we have been talking about for a while, buried between 3 and 6′ deep. The last avalanches it produced were two large slabs on Cornbiscuit, 11 days ago. With more storms comes more loading and all this adds stress to the snowpack. However, it is uncertain whether the loads are big enough to make the deep weak layer more reactive.

In short, deep slab avalanches are notoriously tricky. They can go quiet for days, or weeks, then a small storm or person hitting just the wrong thin spot triggers one. When the uncertainty is high and the consequences are even higher, the only option to manage the problem is by staying conservative with terrain choices. In this case, similar to the travel advice stated above regarding the issues in the top couple feet of the snowpack.

Weather
Wed, January 18th, 2023

Yesterday:  Skies became mostly clear after the storm moved out in the late morning. Around 2-3″ of snow fell from 6am to 10am to finish off a storm total of 14-20″ from Monday night. The easterly ridgetop winds decreased through the day (~20mph to 5) and turned light westerly in the evening. Temperatures were near 30F at lower elevations and in the mid 20’s along the ridges.

Today:  Partly cloudy skies are expected today with light snowfall in the afternoon as another system pushes in. Around 4-6″ of snow could fall, mostly after sunset (snow to sea level). Ridgetop winds will also be on the rise from the east, blowing 20-30mph by this afternoon with gusts in the 40’s or so.

Tomorrow:  Snowfall with strong winds should continue through tomorrow. Models are showing an additional 6-12″ through Thursday (this is on top of the 4-6″ tonight). Easterly ridgetop winds should be in the 20-35mph range with gusts near 50. Temperatures look to rise with this storm, bringing the rain/snow line to 500-800′.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 2-3 0.2 67
Summit Lake (1400′) 20 0 0 32
Alyeska Mid (1700′) 29 2-3 0.2 66
Bear Valley – Portage (132′) 32 0 0.2

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21 NE 13 35
Seattle Ridge (2400′) 24 SE 5 15
Observations
Recent Observations for Turnagain Pass
Date Region Location
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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
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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.