Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, November 25th, 2014 - 7:00AM
Expires
Wed, November 26th, 2014 - 7:00AM
Forecaster
Graham Predeger
Avalanche risk The Bottom Line

The avalanche danger is LOW at and above treeline elevations today.   There still exists a possibility to trigger a wind slab in isolated terrain features, particularly in the higher elevations.   These wind slabs are variable in depth, and at the mid-elevations are resting on a slick rain crust. The continued lack of snow coverage results in No Rating at our lower elevation band below about 1500′.   Another real hazard today deals with the potential for injury from collision with shallowly buried stumps, rocks and other hazards given the early season snowpack.

The next advisory will be Thursday morning (Thanksgiving Day!) at 7am.  
Outlook for Wednesday:  With high pressure building into south-central Alaska today and through Wednesday, the weather and resulting avalanche conditions are expected to be very similar for tomorrow.

Special Announcements

Good morning backcountry enthusiasts!  We’ve got a couple slight changes to the avalanche bulletin that we’d like to highlight:

First, we will be issuing danger ratings for  three elevations bands this season- Alpine (above 2,500-3,000′), Treeline (1,500′ to 2,500-3,000′) and Below Treeline (Below 1,500′). These elevation numbers are not exact since treeline elevations vary across the region. This expansion will help forecasters, as well as the public to better describe and understand the differences in danger and avalanche concerns with respect to elevation.

Second, we have added a new table to the Mountain Weather section that will provide a quick snapshot of precip, temperature and winds at some key weather stations across our region.

Tue, November 25th, 2014
Alpine
Above 2,500'
1 - Low
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
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. 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.
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
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.
More info at Avalanche.org

Surface conditions appear to be shaping up in the Turnagain zone after last weeks onslaught of rain up to about 3,500’ that deposited a stout crust in what is now our mid snowpack.  Yesterday we found variable thickness wind slabs resting on this crust showing signs of good bonding.  This wind slab is capped off by 6-8” of new low-density snow that fell on Saturday and Sunday with very little associated wind.  Though no red flags were noted yesterday and stability tests did not produce any results, confidence in this forecast is low due to limited information and lack of travel into the upper elevations (above 3,000’) thus far.  Where we expect this mid-pack rain crust to finally disappear (~3,500’) wind slabs could be a bit touchier.  Approach these higher elevation alpine slopes with caution and evaluate the snow and terrain carefully before committing to a slope.

 

 

 

 

 

 

 

 

 

 

 

 

                     

 

                              An ‘average’ snowpit in the mid-elevation band.  Sunburst @ ~ 2,900 feet.

Avalanche Problem 2
  • 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

Glide cracks have been mostly covered up by this latest storm.  In this instance though, out of sight does not mean out of mind.  Keep a keen eye out for any new cracks opening up and steer clear of these dangerous features.  Conditions are ripe for new glide crack formation, particularly in the Turnagain area.  There is much to understand about this phenomenon but what is known is that these cracks can release very suddenly and without a real trigger.  Your best bet is to limit your exposure by steering clear of glide cracks.

An additional concern today and for the foreseeable  future involves the hazards associated with an early season snowpack.  Many rocks, stumps and previous glide cracks are thinly covered with this most recent storm.  Keep it conservative and in control, particularly in the lower elevations where snowpack is thinnest.  There is A LOT of winter to still be had and nobody likes being injured, especially early in the season!

 

 

 

 

 

 

 

 

 

 

 

 

Snowpack is thin at the lower elevations.  Expect to hike up to a half hour (Turnagain zone) before putting skis on.

Weather
Tue, November 25th, 2014

Over the last 48-hours we’ve seen 6-8 € of new low-density snow fall at the mid and upper elevations with just a dusting at the highway level (1,000′) through Turnagain pass.   Winds have been the big change over the last 2-days dropping off dramatically as we received this last bout of snow and averaging less than 10mph from the SE.   The rain/ snow line continue its march toward sea level with another ~1,200 -1,400 vertical feet to go.

Today we may see a few lingering flakes in the eastern Turnagain arm area with light winds (4-8mph) from the West.   Temperatures will continue a slight drop today and overnight with lows dipping into the mid-20’s at 1,000′.   This evening and into tomorrow we’ll usher in an upper ridge of high-pressure that should leave us under blue skies and light to moderate winds on Wednesday.

Below are the new weather tables for this season that give a brief snapshot of the past 24-hours for key weather stations in Turnagain Pass, Summit Lake and the Girdwood Valley.
Also, for a more in-depth look at our seasonal weather history click HERE.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31   0 0   19
Summit Lake (1400′) 25    0   0   0  
Alyeska Mid (1539′) 35    0   0   2  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25   SE   5   14  
Seattle Ridge (2400′)  28  variable 7   12  
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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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