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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, January 24th, 2020 - 7:00AM
Expires
Sat, January 25th, 2020 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE for slopes in the Alpine that are being affected by the northwest winds over the region. Watch for wind drifted and loaded slopes where triggering a wind slab up to a foot thick will be possible. Slopes that have not seen wind effect have a generally LOW avalanche danger and encompass much of Turnagain Pass. Keep in mind, the surface snow is very loose and sluffs can be quite large on steep and sustained terrain.

SUMMIT LAKE:  Winds have been stronger in this region and extra caution is advised for triggering wind slab avalanches.

Fri, January 24th, 2020
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.
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

Temperatures have dropped back into the single digits, cloud cover has moved in and winds are generally light this morning near Turnagain Pass. Light snow has been falling in the Whittier and Portage Valley area with only a few snow flurries expected in Girdwood and Turnagain Pass. Wind in the outer-lying regions of our forecast area and snowfall in Portage are our main weather factors contributing to avalanche hazard. The northwest wind picked up yesterday and transported snow along peaks in the Placer and Grandview zone along with those in Summit Lake and south, in the Lost Lake regions. Turnagain Pass was spared much of the wind. Today, winds are expected to be similar, light at Turnagain Pass, but stronger from the northwest in the outer zones.

For today, keep your eye out for recent wind deposited snow and any wind that could be actively transporting snow. Watch for areas with smooth pillowed surfaces, stiffer snow over softer snow and hollow feeling snow. Quick hand pits to look at the top 12-16″ of snow are also great ways to feel if the top layer is slightly stiffer than the snow below. Keep in mind, any wind slab found is likely to be sitting on very weak faceted snow and could be triggered easily. Additionally, the snowpack in general is full of faceted weak layers. The missing ingredient is the slab on top- this is what we need to be on the lookout for.

Thick fog at Turnagain Pass on Wednesday was so moist that it deposited a thin layer of rimed particles over the snow surface between 2,000′ and 3,000′ or so. 1.22.20. Photo taken on Tincan: Allen Dahl.

Avalanche Problem 2
  • Dry Loose
    Dry Loose
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
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

Many folks have reported large and concerning loose snow sluffs in steep terrain. This is a predictable issue and one to consider before entering steep slopes. The old loose facets below Monday’s 10″ of snow can become entrained in a sluff and not only make it larger than expected, but quite heavier as well.

Cornices and Glide Cracks:  As always, limit exposure under glide cracks and give cornices a wide margin.

Weather
Fri, January 24th, 2020

Yesterday:  Partly cloudy skies and some valley fog was seen in most locations. Temperatures dropped to the negative single digits along ridgelines and positive single digits in valley bottoms. Ridgetop winds were light from the northwest at Turnagain Pass, yet a bit stronger to the south near Summit Lake.

Today:  Clouds and a few snow flurries are expected today as a low-pressure spinning in the northern Gulf drifts to the NW. This will push some moisture in from the northeast giving Portage and Girdwood a chance for up to 1-2″ of snow. Ridgetop winds are forecast to remain northeast to northwesterly in the 5-15mph range. Stronger wind is occurring west of Turnagain Pass along the eastern Kenai and southern Kenai toward Seward. Temperatures look to remain in the -10 to -5°F range in the Alpine and in the 0 to 5°F range in valley bottoms.

Tomorrow:  The low-pressure is forecast to slide back to the SE allowing skies to clear tomorrow and cold Arctic air to continue to seeping down into Southcentral. Partly cloudy skies with light to moderate northwesterly ridgetop winds are expected.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 5 0 0 43
Summit Lake (1400′) 5 0 0 15
Alyeska Mid (1700′) 5 0 0 46

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -5 W 2 3
Seattle Ridge (2400′) 1 N 2 4
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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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