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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, January 26th, 2023 - 7:00AM
Expires
Fri, January 27th, 2023 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2,500′. Human triggered avalanches 1-3′ deep on a layer of buried surface hoar remain likely. This type of weak layer can be remotely triggered from low angle slopes onto adjacent steeper terrain. It is also possible to trigger an avalanche on a deeper weak layer 4-8′ deep. We recommend sticking to low angle terrain to give our weak layers more time to heal.

Between 1,000-2,500′ the avalanche danger is MODERATE. Recent wet snow and rain on the surface at these elevations are adding strength to the snowpack. Toward the upper end of this elevation band human triggered avalanches are still possible. Below 1,000′ the avalanche danger is LOW. 

Thu, January 26th, 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. Dangerous avalanche conditions. 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

No new avalanches were reported yesterday. We saw lots of roller balls and some small wet loose avalanches up to about 2500′ on the snow surface, which is an indication of rain or wet snow falling onto a dry snow surface. The last known avalanche on the 1/10 buried surface hoar was on Sunday, January 22nd.

Roller balls and some wet loose avalanches on steeper terrain yesterday, with the possibility of more to come with sunshine and warm temps expected over the next few days. Photo 1.25.23

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

Our last round of precipitation had a pretty high snow line, with wet snow or rain falling up to about 2000′. While this did not do any favors for the skiing and riding conditions at lower elevations, it seems to have added some strength to the upper snowpack and put a damper on the reactivity of the 1/10 buried surface hoar layer. We did not see any new avalanche activity yesterday and for the first time in over a week did not have reactive results in our snow pit tests. However we were only able to check out conditions below 2000′, so it is safe to assume the weak layer is still reactive in upper elevation areas. This is an encouraging sign that conditions might gradually be getting more stable, but due to the track record of the 1/10 buried surface hoar we still think large human triggered avalanches 1-3′ deep are likely above 2000′ today.

We recommend continuing to stick to low angle terrain and being aware of steep slopes above you that could potentially be triggered remotely. It will take time for our weak layers to heal and the consequences of triggering an avalanche remain high due to the depth of the weak layer and potential for very wide propagation. Digging a snow pit is the best way to evaluate the buried surface hoar, but it is worth remembering that older persistent weak layers can tend to give false stable pit results. Which means you could get no propagation in your pit and still have the potential to trigger an avalanche on an adjacent slope.

In addition to our persistent slab problem there was enough wind at upper elevations yesterday to create fresh wind slabs, especially along ridgelines and cross loaded gullies. Wet Loose avalanches and roller balls were visible on a variety of aspects up to about 2500′ yesterday. We are getting to the time of year where if the sun comes out it can create wet loose avalanche conditions and trigger point releases in rocky terrain on steeper southern aspects. Cornices are also looking large on many of our upper elevation ridgelines and the sun can cause cornices to fall onto slopes below. Be aware of the potential for cornice fall if you are travelling underneath a large cornice that is getting direct sunlight.

A new melt freeze crust at lower elevations is adding some strength to the upper snowpack. Photo 1.25.23

Large cornices along upper elevation ridgelines could become more of an issue with stronger solar input and mostly clear skies expected over the next few days. Photo 1.25.23

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

We are still concerned about the same old Thanksgiving crust/facet combination producing very large avalanches at upper elevations. This weak snowpack structure still exists at the base of the snowpack and could produce an avalanche 4-8′ deep. Shallower avalanches like wind slabs or our buried surface hoar could step down to this deeper weak layer. This is yet another reason we are recommending a patient and cautious approach to travelling in the mountains right now. The consequences of being involved with one of these huge avalanches is just too high.

Weather
Thu, January 26th, 2023

Yesterday: Snow and rain tapered off yesterday morning and cloud cover slowly lifted. By the afternoon skies were mostly sunny with patchy layers of valley fog. Moderate winds at upper elevations with averages of 5-15 mph and gusts up to 30 mph. Temperatures were warm, in the mid 30s at lower elevations and upper 20s at upper elevations. Snowline was around 1500-2000′ during the last storm.

Today: Sky cover should trend toward mostly sunny this afternoon with temperatures decreasing slightly to the low 30s at lower elevations and mid 20s at upper elevations as the skies clear. Wind speeds are also expected to decrease this morning to the 0-5 mph range with gusts up to 15 mph. Snow or rain showers are possible today but no significant accumulation is expected.

Tomorrow: Clearing skies and calm winds are expected to persist through the weekend. A temperature inversion is expected to develop Friday evening, with temperatures possibly reaching the low to mid 40s from 1500 – 5000′ from Friday evening through Sunday morning.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 0 0.2 66
Summit Lake (1400′) 32 0 0.1 34
Alyeska Mid (1700′) 33 0 0.25 69.5
Bear Valley – Portage (132′) 38 0 0.37 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26 ESE 9 31
Seattle Ridge (2400′) 29 SE 4.5 16
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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.