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Issued
Fri, January 27th, 2023 - 7:00AM
Expires
Sat, January 28th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger will remain CONSIDERABLE at the higher elevations, above 2,500′. Triggering a 2′ deep slab avalanche remains likely on slopes steeper than 30 degrees. These avalanches are breaking in buried surface hoar and can release after several people have been on a slope. Additionally, give cornices an extra wide berth as some could be close to failure.

The danger is MODERATE between 1,000 and 2,500′ where a 2′ deep slab could be triggered on slopes with a thin breakable surface crust, or no surface crust. The danger is LOW below 1,000′ where just crusty snow exists.

Fri, January 27th, 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

The last known avalanches were from the small but warm storm on Tuesday. Some small wet loose avalanches occurred at the mid elevations and possibly some slabs breaking on buried surface hoar. However, after getting a better look yesterday, it’s uncertain whether those slabs were from Sunday or Tuesday. Either way no significant avalanches have been seen or reported that involved people since last weekend.

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

Another nice day is expected in the backcountry. However, that frustrating layer of buried surface hoar is still there and causing us to remain on our guard. The layer is buried around 2′ deep in most areas and as recently as yesterday, quite reactive. Andrew was able to get 2′ deep shooting cracks and unstable pit results around 3,000′ in Lynx Ck drainage. In the same area but at 2,000′ that layer did not want to react. We are getting to that point where it’s probably less likely to trigger one of these ‘persistent slab‘ avalanches, but we just aren’t sure. Some folks have been able to get on steeper slopes without incident, but that doesn’t necessarily mean that slope is safe; or the slope next to it.

Because of Tuesday’s wet weather event, there is now a not-so-fun surface crust up to around 2,000’. This has changed the slab character, making it much less likely to trigger a slide where that crust exists. Hence, it is now the higher elevations where the snow is much nicer to ride that triggering a slab will be most likely. As we move forward, we don’t want to forget that layer is under our skis, board, or machine. If choosing to start pushing onto steeper slopes, we need to know the risks, have escape routes planned, make sure our partners are watching and do everything we can in the event the slope avalanches. For me, and our recommendation, is to continue playing it cautious on the more mellow terrain. A 2′ deep slab that can propagate across a slope is unmanageable. Couple that with Andrew’s shooting cracks yesterday and enjoying the low angle pow will be just fine.

Sunshine again today ‘may’ be strong enough to soften surface snow and create some roller balls and even small wet loose avalanches. Tomorrow, much warmer conditions are forecast, so this may not occur till then. But this is good to keep on our radar as once the snowpack warms, triggering these 2′ deep slabs could be much easier.

 

Touchy snowpack found in upper Lynx Ck drainage yesterday. 1.26.23.

 

 

Cornices:  These are large and as always, give them an extra wide berth.

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

The warming at the upper elevations, peaking tomorrow, could also impact the Deep Persistent Slab problem – those weak layers surrounding the Thanksgiving crust, buried anywhere from 4-8′ deep. Meaning, the warmth could make those big slabs a hair easier to trigger. As the days go on in general, the chance for these large slabs, that are releasing near the ground, is lessening, but we are still concerned, especially when the weather keeps putting a bit of stress on the snowpack.

Weather
Fri, January 27th, 2023

Yesterday:  Mostly sunny day with light easterly winds along the ridgetops. Temperatures in the mid 30’sF in the lower elevations and in the mid 20’sF along ridgelines.

Today:  Another sunny day is on tap with light westerly winds along ridgetops. Temperatures dropped slightly overnight and some valley fog may be seen today. Daytime temps should be again in the mid 30’F at the lower elevations and in the mid to upper 20’sF along ridgelines.

Tomorrow:  More sunny skies are expected! A warm ‘subsidence inversion‘ is developing which could raise high elevation temperatures into the mid 30’s and even higher. Bring your tanning lotion if you’ll be out. Ridgetop winds should be light and westerly. Some clouds may start to filter in Sunday, but at this point, Sunday is looking pretty nice as well, though a bit cooler.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 0 0 65
Summit Lake (1400′) 30 0 0 34
Alyeska Mid (1700′) 32 0 0 68
Bear Valley – Portage (132′) 37 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24 E 5 19
Seattle Ridge (2400′) 28 SE 5 12
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.