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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, January 18th, 2022 - 7:00AM
Expires
Wed, January 19th, 2022 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE in the Alpine, above ~2,500′. Watch for both new wind slabs (due to moderate east winds expected today) and old wind slabs (formed by last week’s strong east winds). New slabs should be small/shallow and easy to trigger (~6-8″ deep) while the older wind slabs are closer to 1-2+’ deep and much more stubborn.

Below 2,500′, the danger is generally LOW and triggering an avalanche is unlikely. The one exception would be between 2,000′ and 2,500′ where small wind slabs might be found in steep cross-loaded gullies.

*Increasing easterly winds expected through tonight with a several inches of new snow may increase the avalanche danger for tomorrow morning. 

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Tue, January 18th, 2022
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
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

There were no known avalanches triggered yesterday. The last known avalanches were a human triggered cornice fall on Sunday and several natural avalanches with a few human triggered slabs associated with the warm storm last Thursday/Friday. There was a report from an upper elevation southeasterly slope in Lynx drainage of a more recent looking natural slab, which may have occurred over the weekend.

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • 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.
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 a couple sunny days to round out the Martin Luther King Jr. holiday weekend, clouds have moved back in with a few snow flurries. There is a weak weather system over the region that should peak late tonight/early tomorrow. For today’s daytime hours, the ridgetop easterly winds are increasing to 15-20mph with stronger gusts and will increase further to 25-30mph tonight. Snowfall should only be a trace today but we could wake up to 2-4″ tomorrow morning. That said, wind slabs will remain our main concern.

If you are headed out today, look for any signs of current or prior wind loading, predominantly above 2,500′. There should be enough snow available to transport to form new slabs (in the 6-8″ range) through the day. If winds increase quicker than forecast, your travels back to the parking lot could have more wind effect and wind slab development along ridgelines. As always, watch for stiff snow over softer snow and especially any cracking or whumpfing in the snow around you.

Wind slabs on weak snow? After chatting with the skier who triggered large cracks on a wind loaded slope in upper Girdwood Valley on Sunday, it was determined that the large wind slab could be sitting on weak facets over the New Year’s crust. This area has a shallower snowpack making it a lot easier for wind slabs to form on the crust. The take home here is watch for those red flags and be more suspect in areas where the snowpack is thinner in general (west side of Girdwood Valley and the south end of Turnagain Pass toward Summit Lake).

Cornices:  If getting up to the ridgelines today, be sure to give cornices an extra wide berth.

A new generation of surface hoar is beginning to form on the surface. This photo is from the SW face of Lipps ridge. 1.17.22.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • 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.
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 continuing to track the New Year’s crust (buried anywhere from 2-5′ deep) and any weak snow that might still be an issue above or below it. So far evidence is pointing to a more stable snowpack, especially in areas with little wind loading. There are also a few buried crusts with looser snow around them within last week’s storm snow below 2,000′. These also have shown signs of bonding. All good news moving forward and triggering a deeper avalanche has become unlikely. Even so, especially in areas with little or no traffic yet this season, we should have our eyes out for any outliers.

Weather
Tue, January 18th, 2022

Yesterday:  Mostly clear skies transitioning to high clouds midday. Ridgetop winds were 5-10mph from the east with a few gusts in the teens. Temperatures have been steady in the teens at all elevations save for some chilly valley bottoms in the single digits.

Today:  Cloudy skies and a chance for a few snow showers will be over the region. Only a trace to an inch at most is expected at all elevations today with 2-4″ possible late tonight into Wednesday. Ridgetop winds have been increasing overnight and should blow 10-20mph from the east today and 20-30mph tonight with the snowfall. Temperatures should remain near 20 at mid elevations and teens up high.

Tomorrow:  Cloudy skies with some lingering snow showers are forecast for Wednesday. Winds along the ridgelines should be in the 20mph range and decreasing through the day. Temperatures should remain in the 20’sF with the teens along the peaks.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 21 0 0 78
Summit Lake (1400′) 12 0 0 28
Alyeska Mid (1700′) 21 0 0 N/A

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 16 E 11 25
Seattle Ridge (2400′) 16 SE 8 15
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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.
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