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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, December 6th, 2023 - 7:00AM
Expires
Thu, December 7th, 2023 - 7:00AM
Forecaster
Graham Predeger
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 2,500’ today.  Shallow wind slabs in the 1-2’ range will be possible to trigger in the upper elevations near ridge lines, convex rollovers and steeper gullies.  There are some deeper layers in the snowpack that we’re keeping an eye on but will be unlikely for a person to trigger today.  Below 2,500’ the avalanche danger is LOW.

Special Announcements

Become a Member in December! The Friends of the Chugach Avalanche Center is a non-profit, which means we need your help to keep our avalanche center running. This is our most crucial time of year for fundraising, so if you haven’t yet, please consider becoming a member. Did you know that nearly half of our Forest Service avalanche specialists’ positions are funded by community donations to the Friends, as well as 100% of the new Chugach State Park Avy Specialist’s position? Everyone who donates will be entered to win some awesome prizes (like Dynafit bindings, a Voile splitboard, and more!) at our Girdwood Brewery Forecaster Chat on January 19.

Join Alaska Safe Riders and professional snowmobilers Dan Adams, Matt Entz, and Dustin Pancheri for an Avalanche Awareness Open House to prepare for your next mountain adventure.  They’re in Fairbanks tonight and Anchorage on Friday.  All the details can be found here.

Wed, December 6th, 2023
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
Thu, December 7th, 2023
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
Thu, December 7th, 2023
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

The last known human-triggered avalanche reported was a small wind slab pocket on Tincan, on Friday (12/1).  Beyond that, we’ve seen evidence of a natural avalanche cycle that ramped up as last week’s storm was winding down on 11/30.  Crowns were reported from Main bowl and Warm up bowl on the moto side of the highway to Sunburst and upper Bertha Creek on the non moto side.

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

It was a pretty quiet weather day yesterday with light winds, cooling temps and no real precipitation to speak of.  Given that lack of weather input, we dropped the danger rating in the treeline elevation band to LOW danger today.  Low danger does not mean no danger and isolated areas below treeline still have the potential to nurture wind loaded pockets.  However, the most likely places to find unstable snow will be in the alpine, above ~2.500’ where winds have redistributed last week’s fresh snow into shallow wind slabs.  Below ridge lines , steep gullies or convexities where a slope  begins to roll over into steeper (greater than 30 degree) terrain should all be seen as suspect and have potential to harbor wind slabs in the 1-2’ range.

This is a ’normal caution’ regime and while not an overly dangerous avalanche problem, keep in mind that skiing/ riding above terrain traps (trees, cliffs, gullies, creeks, etc.) amplifies the consequences should a slope slide.  Keep eyes on your partners, communicate intentions and as always, be rescue ready. 

Currently, the Summit Lake zone has a similar snowpack set up as the Turnagain area.  Click on the video below for an update from new Chugach Avalanche forecaster Daniel Krueger who’ll be keeping tabs on, and issuing a weekend avalanche outlook for this area and points south on the Seward Ranger District this winter. 

Additional Concern
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

‘In this world there’s two types of crusts my friend.  Those that prove problematic, and those that go dormant.’Quote adapted from The Good, the Bad and the Ugly

The Good: We’ve seen literally thousands of tracks on all aspects and elevations from skiers and snowmachiners testing the Thanksgiving crust since it was buried last week, with minimal avalanche activity.  Snowpit tests results have been mixed but overall are showing the late November storm has bonded well to this crust.    

The Bad: Crusts are notorious for ‘waking up’ down the road as the snow weakens and facets out above and below these layers.  Buried crusts can often support a significant load before avalanching, or may just become dormant with time.  Click here for some ‘Ruminations on Rain Crusts’ from our neighbors to the East.

The Ugly:  This crust is quite widespread throughout the advisory area and has been found in all snowpits (up to 3,400’ and likely higher) over the past week.  As such, if this layer becomes reactive it has potential to be a region wide problem, extending across multiple different zones and through elevation bands. 

The Thanksgiving crust interface isn’t our greatest concern today, but it’s an obvious marker within our snowpack and one we’ll be keeping tabs on in the days and weeks ahead. 

The snowpack in Summit Lake area and Turnagain Pass is quite similar right now with the Thanksgiving crust buried in the mid-pack and quite easy to suss out, even with a quick hand pit.

 

Weather
Wed, December 6th, 2023

Yesterday: Mostly cloudy skies, light winds from the Northwest and falling temperatures made for a pretty quiet weather day.  No new precip was measured in the core advisory area.

Today: We can expect mostly cloudy skies with the chance for 1-2″ of snow to sea level.  Temperatures have fallen since yesterday with ridgetop weather stations reporting in the low teens F this morning.  At 1,000′ temps are expected to be hovering around the low 20s F.  We may see a slight bump in winds this afternoon from the Northwest before slacking off overnight.

Tomorrow: Temps will stay cool and winds calm with partly sunny skies in the morning.  Clouds and light snow showers move in tomorrow afternoon as more active weather lines up ahead of the weekend.  Any snow that does fall will be to sea level for the foreseeable future.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 25 0 .1 50
Summit Lake (1400′) 24 0 0 21
Alyeska Mid (1700′) 24 1 .1 33
Bear Valley – Portage (132′) 29 3 .33

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 17 NW 3 11
Seattle Ridge (2400′) 21 NW 3 13
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.