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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, January 5th, 2023 - 7:00AM
Expires
Fri, January 6th, 2023 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2500′ today. Wind slabs up to 2’+ deep that formed over the past 24 hours are likely for human triggering, especially along upper elevation ridgelines. It is also still possible for a person to trigger a larger avalanche on a buried weak layer 2-4′ deep. Conservative terrain selection and decision-making is recommended.

From 1000′ to 2500′ the avalanche danger is MODERATE. Isolated wind slabs and avalanches on deeper weak layers are possible towards the upper end of this elevation band. Below 1000′ the avalanche danger is LOW. 

SUMMIT LAKE: A skier remote triggered an avalanche on Tenderfoot on Jan 4th at about 2000′ on a NW aspect. Remote triggering is a major warning sign and a reminder to be conservative with terrain selection and be aware of steeper slopes above you!

Special Announcements

Join us at the Girdwood Brewing Co. from 5:30-7:00 p.m. on Thursday, Jan. 19 for the second Forecaster Chat of the season. 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.

Filing your PFD application? Our non-profit partner the Friends of Chugach Avalanche Center is an official Pick. Click. Give. organization, so please consider donating part of your PFD to support our avalanche forecast and public avalanche safety mission!!!

Thu, January 5th, 2023
Alpine
Above 2,500'
3 - Considerable
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

Turnagain Pass:

During our field day on Pete’s N yesterday we observed several large avalanches on surrounding peaks. The exact age of these is hard to tell from a distance, but our best guess is that they include the storm snow from the New Years storm and possibly older layers from the Christmas storm or deeper. The largest avalanche we observed was at 3000′ on the E aspect of Twin peaks. Another similar looking avalanche up Lynx creek at 3000′ on a N aspect. Finally, on the SW aspect of Lipps at 2800′. These all had relatively wide propagation and released mid slope, which we think is an indication that a persistent weak layer exists at these mid elevations.

Large avalanche on E face of Twin Peaks mid way down the slope. You might have to zoom in to see it, but it is lookers left of Twin Peaks at treeline on the forested ridge in the foreground. Photo 1.4.23

Smaller avalanche on the SW face of Lipps at 2800′. This crown is partially filled in with the strong winds yesterday morning, but looks like it is within the storm snow from Christmas and New Years. Photo 1.4.23

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

After several large storms this week, including 2-3′ of snow from the New Years storm and 0.5-1.5′ of snow falling on Wednesday, the snowpack needs some time to adjust to the new load. We have seen some large avalanches in the aftermath of these storms and are uncertain what weak layers are the culprit. The weather pattern is expected to calm down today which will decrease the likelihood of natural avalanches and give the snowpack time to gain strength.

Wind slabs up to 2’+ deep which formed at upper elevations over the past 24 hours are the primary avalanche problem today. These are likely for human triggering and typically found along ridgelines and gully features above treeline. To identify wind slabs look for deposits of deeper snow that have a firmer and possibly hollow feeling snow surface. Using small test slopes is a great way to see if wind loaded slopes are still reactive to the weight of a skier or rider. Due to uncertainty around the presence and distribution of persistent weak layers above 2000′ we are still recommending a conservative approach to terrain selection and decision-making today (see problem 2 for more details).

Strong E winds yesterday morning were rapidly building fresh wind slabs at upper elevations. Photo 1.4.23

Avalanche Problem 2
  • 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

We are still trying to piece together how the recent storms have impacted our existing persistent weak layers and possibly created new ones. The message is pretty simple though, very large avalanches 2-4′ deep above 2000′ are still possible. The best way to mitigate the risk from persistent slab avalanches is to stick to smaller terrain features and lower angle slopes.

The combination of a remote triggered avalanche in the Notch Peak area in Girdwood and several large avalanches on the southern end of Turnagain Pass near the Johnson Pass trail head have us scratching our heads a bit about what weak layer(s) is responsible. Most of this recent activity has been at mid elevations and releasing mid slope, which indicates that there is a weak layer that is most prominent around 2500-3000′. Our best estimate is that this is related to a weak interface between the mid-December facets and all the storm snow that fell during the Christmas and New Years storms, but there is a lot of uncertainty since we have not been able to investigate any of these avalanches in detail yet.

 

Weather
Thu, January 5th, 2023

Yesterday: The remnants of the quick moving storm from Tuesday night combined with a few additional pulses of snowfall during the day Wednesday brought an additional 0.4″ to 0.8″ of water, which is around 5-10″ of new snow, to the forecast area. Strong winds at upper elevations peaked yesterday morning with averages in the 20-30 mph range and gusts up to 60 mph. Wind speeds decreased slightly in the afternoon and overnight with averages of 15-20 mph and gusts to 35 mph.

Today: Some lingering snow showers could move through the area this morning, but no real snow accumulation is expected. Winds should ease off by midday with averages dropping to the 0-10 mph range. Temperatures are also expected to decrease from the twenties to teens F at mid and upper elevations. Cloud cover should decrease throughout the day.

Tomorrow: Winds should shift to the NW by Thursday evening and remain mostly light at 0-10 mph through Friday. Some areas exposed to typical NW gap winds could see elevated wind gusts up to 25 mph, like Turnagain Arm, Portage, and Seattle Ridge. Temperatures are expected to remain in the teens with mostly clear skies. No new snow is expected until Saturday night into Sunday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30 5″ 0.4 65
Summit Lake (1400′) 26 2″ 0.2 33
Alyeska Mid (1700′) 31 9″ 0.8 55
Bear Valley – Portage (132′) 38 0″ 0.7

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22 ENE 21 60
Seattle Ridge (2400′) 26 ESE 11 38
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.