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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, February 22nd, 2016 - 7:00AM
Expires
Tue, February 23rd, 2016 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger continues to be HIGH in the Turnagain Pass and surrounding mountains. Between 3 and  4+ feet of heavy snow has fallen in less than two days resulting in very large and widespread avalanche activity. Today, the storm has abated but dangerous avalanche conditions still exist. Large natural avalanches, running to the valley bottoms, are still possible. For people traveling in the backcountry, avoiding all avalanche terrain, slopes 30 degrees and steeper, including runout areas in the flats, is recommended.  The danger is MODERATE below 1,000′ where debris from an avalanche above may run.

This travel advise and warning extends to the Summit Lake area as well where dangerous avalanche conditions exist. See Saturday’s  Summit Lake Summary  at this link.

**Today is a day to be patient and let the snowpack adjust to this new load of heavy snow.

Special Announcements

 

  • Avalanche Hazard Reduction work will be conducted on the Seward Highway from MP 82 to MP 99. Expect traffic delays up to 45 minutes today, Monday, from 9am-3pm. More details can be found at 511.alaska.gov.
Mon, February 22nd, 2016
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
More info at Avalanche.org

It was quite a day in the mountains yesterday as a fast moving storm rolled through. A “mini-snow-pocalypse” of sorts that dropped several feet of snow in ~30 hours!! See storm totals below. This was a text book ‘rapid loading’ event and it is no surprise that widespread and large avalanche activity resulted across the region. With such limited visibility we only saw the aftermath of the activity, in the form of debris piles – photos below. However, one person did get a glimpse of the terrain later in the day:

Quote from frequent and longtime skier in the Turnagain Pass area, Eric Opland:
Going through Turnagain it started to clear and we saw fractures on almost everything, including one that included most of the Sunburst cornice lines. Then when getting close to the Placer river we watched another slide happen on the first peak to the east of the Portage road off a south aspect, again decent size.” Read the entire write up HERE.

Storm totals since Saturday morning. Keep in mind the rain snow line hovered around 1,000-1,200′.

                               Snow above treeline      Water Equivalent
Girdwood Valley:            3-4 feet                          4.5″ H20
Turnagain Pass:             3-4 feet                          4.0″ H20
Summit Lake:             16-26 inches                      2.0″ H20

For today, skies will hopefully clear enough to see above treeline so we can take stock of yesterday’s damage. Again, although the storm is over, the snowpack is still suspect to being very unstable. The new snow fell on a variety of surfaces, many of which are weak (surface hoar and weak faceting snow). How long it will take the new and old snow interface to bond is a big uncertainty at this point and very conservative terrain choices will be necessary as we move into the week.

Adding to the instability today will be continued Easterly winds (20-30mph) that will keep loading slopes and building cornices. In the event there is a true break in weather and the sun comes out, the sun will act to de-stabilize the pack as well. Needless to say, give the mountains a break today. Travel on slopes more than 30 degrees and in runout zones (including valley bottoms) is NOT recommended. 

Photo: Debris piled up in the Peterson drainage area along the Seward Highway between Portage and Girdwood.
  

 

It was a pretty crazy day at the Pass, see Aleph’s quick video below for an idea:

  

Photo: More debris along the Southern end of Seattle Ridge. With such limited visibility we did not see above treeline.

 

Avalanche Problem 2
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Cornices are likely to be a main player today in avalanche activity. After a storm like we just had, cornices should have grown, be on the verge of falling and could trigger very large avalanches below that could run to valley bottoms. Many likely broke off during the storm, triggering avalanches that we have yet to see due to the lack of visibility yesterday. With either continued wind or even some sunshine today, both these weather factors can aid in tipping the balance for a natural cornice fall. Just one more reason to give the mountains some patience today.

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

With the chance for visibility today, we will be looking out for any new glide cracks that released during the storm. In an effort to document this season’s unique glide activity, we are keeping track of when and where glide cracks form as well as release. As always, limit/and or avoid exposure under glide cracks.

Weather
Mon, February 22nd, 2016

During the daylight hours yesterday we saw the peak of the storm cycle and then during the overnight hours, its end. Precipitation quieted down around 6pm after roughly 16-20+” of snow fell during the day above 2,000′; this is on top of the 16-20″ from Saturday. The rain/snow line began around 500′ at the onset of the storm Saturday then rose to 1,200′, or a bit higher, at the peak. Strong Easterly winds have been in place during the past 48-hours, averaging 30-50mph with stronger gusts. Overnight, temperatures have cooled and are ~32F at 1,000′ and the mid 20’sF at 3,500′.  

Today, we are expecting instability showers over the area bringing partly to mostly cloudy skies and a chance for 2-6″ of snow at the higher elevations. We could even see the sun break through in areas. Temperatures should rise a bit (~35F at 1,000′) bringing the rain/snow line to ~1,200′. Easterly winds along the ridgelines are expected to remain moderate to strong in the 20-30mph range.

For Tuesday, another low-pressure system makes its way North from the Pacific bringing warm temperatures and moisture. We could see higher rain/snow lines with this system and another dose of 2-3″ of water – stay tuned.

Photo: A true storm day on the Pass.
 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31   8-10″   2,0   125  
Summit Lake (1400′) 29   6-8″    1.1 (suspect number) 40  
Alyeska Mid (1700′) 32   3-5″ 2.6   98  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 NE   34   85  
Seattle Ridge (2400′) 25   SE   31   86  
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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.