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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, January 30th, 2023 - 7:00AM
Expires
Tue, January 31st, 2023 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′. It is possible for a person to trigger a large avalanche on a weak layer of surface hoar buried 2-3′ deep. It is also possible to find reactive wind slabs that formed in the past 24 hours on isolated upper-elevation slopes. If you plan on moving into steeper terrain, take the time to assess these issues and start with smaller terrain features that minimize the consequences of triggering an avalanche. You can avoid these problems entirely by sticking to low-angle slopes. The danger is LOW below 1000′.

SUMMIT LAKE: The Summit Lake area has a similar, but thinner and weaker snowpack than Girdwood and Turnagain Pass. This makes human-triggered avalanches a little more likely, which means steeper terrain should be approached with more caution.

Mon, January 30th, 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
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

The last reported natural activity was on Saturday when sunny skies and warm temperatures triggered wet loose avalanches that were pulling out small slabs in some cases. The last known human-triggered avalanches were 9 days ago, with multiple people getting caught and carried in avalanches failing on buried surface hoar.

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

We are slowly seeing evidence that the layer of buried surface hoar (now 2-3′ deep) that has been the culprit for many natural and human-triggered avalanches is gaining some strength. It has now been 9 days since the last human-triggered avalanche on this layer, and it is becoming harder and harder to find unstable test results or warning signs like shooting cracks or collapsing. Although it is still possible to trigger an avalanche on this layer, it is feeling less dangerous now than it was a week ago.

With a little more confidence in this weak layer, we are slowly starting to move back into steeper terrain. This needs to be done carefully, which means taking the time to assess the snowpack for the zone you are traveling in and choosing terrain wisely. At this point we are just dipping our toes in the water, not diving into the deep end. There is still some uncertainty with just how reactive the layer is, and you can minimize the consequences of triggering an avalanche by choosing smaller terrain with clean runout zones free of terrain traps like gullies, cliffs, trees, or rocks. For this type of problem, it is worth taking the time to dig a quick pit to test the layer as one final check before jumping on steeper slopes. If you get an unstable result, it’s a sign to stick to low-angle terrain. As always, only expose one person at a time, and keep an eye on your partners from safe spots out of avalanche runout zones. The lingering potential for triggering a massive avalanche on the Thanksgiving crust/facet layer deeper in the snowpack (see problem 2) should be one more reason to stay on smaller terrain for now. Remember, you can avoid this problem entirely by sticking to slopes less than 30 degrees.

Wind Slabs: It is likely some wind slabs formed with moderate easterly winds over the past 24 hours. These will remain reactive on isolated upper elevation slopes today. Be skeptical of steep slopes just below ridgelines, in steep gullies, or on convex rolls. Avoid steep terrain with stiff snow on the surface sitting on top of softer snow. There is a chance that a relatively small wind slab avalanche could step down to the buried surface hoar layer, triggering a larger avalanche.

CNFAIC intern Megan Guinn checking out our surface hoar layer on Max’s before we got into the steeper terrain near the top. 01.29.2023

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

Even though it is becoming less likely, we aren’t quite ready to ignore the weak layers of facets surrounding the Thanksgiving crust. This is now buried around 4-8′ deep on average. It has been over three weeks since the last human-triggered avalanche on this layer, and two weeks since a natural avalanche stepped down to the layer. This layer is most problematic in areas with a thinner snowpack at elevations above 2500′. Although it is unlikely a person will trigger an avalanche on a layer that deep, the consequences of getting caught in something that big would be severe. This is just one more reason to be careful in the way you approach moving into steeper terrain, starting with smaller features and letting the ‘big game’ terrain wait for now.

If the video below doesn’t load in your browser, you can click here to view it.

Weather
Mon, January 30th, 2023

Yesterday: Skies were cloudy with light snow showers off and on through the day. We only picked up 0.1” precipitation equaling around an inch of snow, with the rain line staying around 100-200′. High temperatures were in the upper 20’s to low 30’s F, with overnight lows in the low 20’s to low 30’s F. Winds were blowing out of the east at 10-20 mph with gusts around 25 mph.

Today: It is looking like another quiet day weather-wise. Skies should be cloudy with light easterly winds blowing 10-15 mph at ridgetops this morning and calming to 5-10 mph through the day. We might see a trace of precip with snow down to 800-1000’, with no significant accumulation expected. High temperatures should reach the upper 20’s to low 30’s F today, dropping down to the mid to upper 20’s F tonight.

Tomorrow: Temperatures will cool slightly, with highs in the mid to upper 20’s F and light northwesterly winds around 5 mph. Skies should be mostly cloudy skies with some breaks in the clouds possible through the day. No precipitation is expected tomorrow. The weather is looking pretty benign for the week with our next chance for significant precip picking up next weekend.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 1 0.1 64
Summit Lake (1400′) 25 1 0.1 59
Alyeska Mid (1700′) 31 2 0.14 65
Bear Valley – Portage (132′) 36 rain 0.23

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 E 13 27
Seattle Ridge (2400′) 26 SE 12 20

 

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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.