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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, February 1st, 2023 - 7:00AM
Expires
Thu, February 2nd, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′. It remains possible that a person could trigger a slab avalanche around 2 feet deep that breaks on a hidden layer of buried surface hoar. Slopes at elevations above the surface crust are the most likely places to trigger a slide. The danger is LOW below 1000′ where the snowpack is mostly crusts.

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

Wed, February 1st, 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

No avalanche activity has been reported or seen since last Saturday’s warm up; several wet loose avalanches released with some pulling out small slabs on steep southerly slopes. The last known human-triggered avalanches were 11 days ago (1/21). Multiple people were caught and carried in avalanches failing on a layer of buried surface hoar around 2′ deep.

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

Fabulous February begins! Our days are 2 hours and 20 minutes longer since the winter solstice and now all we need is a fresh round of snowfall – to sea level. Until then, the snowpack is continuing to stabilize, yet we are still chirping about the buried surface hoar that sits a couple feet deep. We found this layer easily again yesterday south of Turnagain Pass in the Johnson Pass area. We did not see any signs of instability, and could not get the layer to react in our snow pit. Great signs. Evidence is still pointing to a healing weak layer. However, we know these weak layers can pull out surprises and that’s what we have to watch out for.

If venturing out today, remember a weak layer exists around 2-3′ deep and we could trigger an avalanche in just the right spot. Slopes above ~2,000′ that do not have a surface crust are the most suspect. Tracks on a slope doesn’t necessarily mean it’s stable and we are not likely to see any signs of instability. This is the tricky nature of old buried weak layers. Venturing out into untraveled areas is also suspect.

Following safe travel protocol is our best friend if choosing to push into the steeper terrain. This means exposing one person at a time, having our escape routes planned, making sure our partners are watching and know how to effect a rescue if the slope suddenly releases. As we’ve also been saying, to avoid all this uncertainty we can keep it mellow and just stick to slopes ~30 deg. or less.

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

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

If you’ve been reading this far down in the forecast for the last month, you know that we aren’t quite ready to put to bed that facet/crust combo that sits around the Thanksgiving Crust. This old complex of weak snow and crusts is buried 4-8’ deep and would be very unlikely that a person could trigger it. However, in shallow zones such as the Summit Lake area to the south of the forecast zone, the possibility is slightly greater due to the thinner pack. If headed out to the thinner snowpack areas keep this layer in mind too.

Weather
Wed, February 1st, 2023

Yesterday:  Partly cloudy skies were over the region with the sun shining in some locations. Ridgetop winds were impressively calm. Temperatures were mild, near 30F at the lower elevations and mid 20’s along ridgetops.

Today:  Cloudy skies will be over the region today with a chance for a few flurries. Only a trace of snow is expected to accumulate. Ridgetop winds are slated to be light, ~5mph, from the east to southeast. Temperatures should remain near 30 at the lower elevations and in the mid 20’sF along ridgelines.

Tomorrow:  Similar conditions are expected for tomorrow and through Saturday. Mostly cloudy skies, some snow flurries, light easterly winds. Temperatures look to be on a cooling trend into Saturday. The next round of decent snowfall might be developing for Sunday/Monday. Stay tuned!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28 0 0 63
Summit Lake (1400′) 26 0 0 33
Alyeska Mid (1700′) 28 0 0 64
Bear Valley – Portage (132′) 30 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 variable 1 6
Seattle Ridge (2400′) 25 variable 1 6
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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.