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Issued
Sat, December 2nd, 2023 - 7:00AM
Expires
Sun, December 3rd, 2023 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′ today. Cold and dry weather starting yesterday morning is giving the snowpack time to adjust after 2-3′ of new snow this week. We recommend assessing how well the new snow is bonding to the old snow surface before committing to steep terrain. Lingering wind slabs 1-2′ deep along ridgelines are the most likely type of avalanche you could trigger today. Below 1000′ the avalanche danger is LOW. At these lower elevations the recent storm fell as rain which has created an icy crust on the surface.

Special Announcements

Headed to Seward, Summit Lake, or Chugach State Park today? Check out the inaugural edition of our weekend outlook products!

Sat, December 2nd, 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
Sun, December 3rd, 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
Sun, December 3rd, 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

Yesterday offered the first good visibility for spotting avalanches since the recent stormy weather began last week. We observed one likely avalanche on the SW face of Sunburst around 3600′, occurring at the new snow and old snow interface. Similar avalanches were noticed on the N side of the Magnum ridgeline and the south face of Tincan Proper. Silverton Mountain Guides, flying from Seward to Portage, reported substantial natural avalanche activity in the Skookum and Spencer glacier drainage areas, likely happening on Thursday during the peak of the snowfall. Currently, these areas are inaccessible due to low snow cover at sea level.

Sunburst natural avalanche that likely released on Thursday. Crown shown in red and approximate track in blue. Possibly triggered by cornice fall from above. Photo Jon Davis 12.1.2023

Partially filled in crown on the S face of Tincan Proper which likely released during the storm on Thrusday. Photo from Rafeal Pease 12.1.2023

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 is shaping up to be a fine weekend for mountain recreation in the Turnagain Pass area. After 10 days of wet and stormy weather, the skies finally cleared yesterday to reveal a fresh 2-3′ of new snow down to 1000′. The weather is expected to stay cold with light winds and partly sunny skies throughout the weekend. Due to the recent stormy weather we have limited information from the forecast area. There were a few observations of natural avalanches that released during the storm on Tincan, Sunburst, and Magnum. Lots of folks were out yesterday, and we have not heard of any significant human triggered avalanches.

The most likely type of avalanche you could find today is a wind slab lingering in steep terrain that formed during the storm. Wind slabs are commonly found near upper elevation ridgelines or convex rolls near treeline. You can check whether wind slabs are reactive by jumping on or riding across small, steep test slopes and looking for shooting cracks or small avalanches. Stepping out of the track and feeling for areas with firmer snow on top of softer snow can also be an indicator to help locate areas that have been recently wind loaded. If you plan to venture into the steeps today, we recommend gradually working your way up to steeper slopes and evaluating how well the new snow is bonding to the old snow surface before committing to exposed terrain.

At elevations above 3500′ there is a layer of weak faceted snow at the ground which could be cause for concern in areas with a thinner snowpack. Locations where this could be an issue include high elevation peaks near Johnson Pass, Silvertip, or Crow Creek area. These places typically have a shallower snowpack, therefore initiating an avalanche on a buried weak layer at the ground is more likely.

Thanks to Travis, Graham and all those who cleared the rime off Seattle Ridge Wx Station! Photo Travis Smith 12.1.2023

Weather
Sat, December 2nd, 2023

Yesterday: Winds died down yesterday morning, with a few hours of averages of 15-20 mph and gusts to 35 mph in the early morning before dropping to averages of 0-5 mph and gusts less than 10 mph for the rest of the day. There was no new snowfall across the forecast area in the past 24 hours. Temperatures were in the 20s F and cloud cover was scattered.

Today: Dry and cold weather is on tap for today. Light winds out of the NE are expected, with averages of 0-10 mph. Temperatures should be in the teens to 20s F. Skies will remain partly cloudy. No significant new snowfall is expected.

Tomorrow: Sunday is looking very similar to Saturday, with light winds in to 0-10 mph range, temperatures in the teens to 20s F and partly cloudy sky cover. No new snow is expected until Monday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24 0 0 54
Summit Lake (1400′) 18 0 0 22
Alyeska Mid (1700′) 26 0 0 38
Bear Valley – Portage (132′) 29 0 0.02

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 WSW 5 35
Seattle Ridge (2400′) 22 NE 1 5
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.