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Thu, April 11th, 2019 - 7:00AM
Fri, April 12th, 2019 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE today above 2500′. Triggering a wind slab up to 12 € thick will be possible on steep leeward features due to strong wind and new snow. Below 2500′ the avalanche danger is MODERATE where triggering a wet loose avalanche is possible. Avoid traveling below glide cracks and cornices. Should the sun make an appearance later in the day, natural wet loose activity in the alpine on solar aspects will be possible.  

PORTAGE VALLEY:  There is very little snow below 1000′, but Summer trails with large steep slopes directly overhead, such as the Byron Glacier Trail, provide easy access for accidentally being in a dangerous place. Today’s strong winds and heavy precipitation could trigger cornice fall or a wet avalanche into the valley below. Travel in these areas is not recommended.

Thu, April 11th, 2019
Above 2,500'
3 - Considerable
Avalanche risk
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
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

A storm has moved into our region bringing strong winds, rain and heavy snow above 2000’. Overnight Easterly ridgetop winds increased into the 30s mph with gusts in the 60s mph. Winds will remain strong all day. An estimated 2-4” of snow has fallen overnight in the upper elevations of Turnagain and Girdwood. Portage has seen heavy rain. An additional 6-12” of new snow is expected in the upper elevations (0.6-0.8” of rain) for Girdwood and the North end of Turnagain Pass. Interior areas will see less precipitation. Wind slab size will depend on how much snow falls in the area you are traveling.

New snow will be falling on a variety of slick surfaces and bonding may be poor. Today’s visibility will make for difficult travel in the alpine due to blowing snow. Be on the lookout for shooting cracks and avoid slopes steeper than 35 degrees. Look for pillowed snow along ridgelines and be cautious of fresh drifts. Small natural wind slabs are possible in very steep channeled terrain due to the intensity of wind. Cornices will also be growing and could release naturally.

WET LOOSE: In the lower elevations below 2000’ triggering a wet loose avalanche will become possible as rain starts breaking down surface crusts. If the snow becomes wet and unsupportable avoid steep terrain features and terrain traps. **Keep in mind it’s springtime and be ready for wet loose activity in the alpine if the sun comes out and starts heating up the new snow. This is more likely further from the coast as the storm front moves out of the region.

Slick Crusts exist on W-S-E aspects in the alpine (left photo) and a 4-6″ of soft snow is sitting on near surface facets and buried surface hoar on some North aspects (photo on right.) 



Corniced Ridge in Girdwood Valley – Cornices will be growing today with strong wind and new snow. Give these features lots of space along ridge lines and avoid being under them.

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Although it has been several days since we have seen a glide crack release into an avalanche, avoiding/limiting travel under cracks is prudent! They can release at anytime, are completely unpredictable and can be very destructive. Identify existing cracks and plan your route to avoid being under a glide.

Thu, April 11th, 2019

Yesterday: Skies were partly cloudy in the morning becoming mostly cloudy later in the day. Temperatures reached the mid-40Fs at sea level. Upper elevation temps were in the mid-20Fs to low-30s. Ridgtop winds were 5-15mph from the East building overnight into the 30mph with gust in the 60s. Rain started falling overnight and .2 € of SWE was recorded in Turnagain Pass with 1″ of wet snow. Bear Valley in Portage has recorded .7 € of rain in the last 24hrs. Rain/snow line is estimated around 1800′.

Today: In the upper elevation 6-12 € of snow is expected in the alpine, with 0.6-0.8 € rain at lower elevations. Rain/snow line should be around 2000′. Areas further from the coast will see less precip today. Easterly ridgetop winds are expected to be 35-50mph with stronger gusts. Temperatures at sea level will be in the mid-40Fs, temps along ridge tops may reach the upper-20Fs. As the storm moves out of the area, winds and precip will decrease overnight.

Tomorrow: Scattered rain and snow showers are expected – light rain below 2000′ and a few inches of snow possible in the upper elevations. Easterly Ridgetop winds will be 10-20mph.Temperatures at sea level will be in the mid-40Fs and ridgetop temps in the low-30Fs during the day.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 36   1   0.2   62  
Summit Lake (1400′) 38   0   0   18  
Alyeska Mid (1700′) 37   1   .27   55  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26   ENE    18 71  
Seattle Ridge (2400′) 29   SE   13   31  
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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.