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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, April 13th, 2013 - 7:00AM
Expires
Sun, April 14th, 2013 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is LOW in many areas.   Shallow wind slabs up to a foot in depth and loose snow avalanches will be easy to trigger in upper elevation starting zones.   In these areas the avalanche hazard is MODERATE today.

Sat, April 13th, 2013
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. 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

We have received reports of several human triggered wind slabs over the last several days.  Yesterday my partner and I were able to release one of these slabs on a steep rollover on a west facing slope, as pictured below:

Lipps 4-13

Expect more of the same today.  The warm temps of last week helped to form stout crusts on all but north facing upper elevation slopes.  Since that time we have seen less than a foot of new snow accumulation on Turnagain Pass and closer to a foot around Girdwood.  The last three days of clear and cold weather has helped to weaken the snow, particularly at the interface between these crusts and whatever new snow has fallen over the past ten days.  In areas that received wind loading in the last several days these shallow slabs will be sensitive to the weight of a person today.

Avalanche Problem 2
  • Dry Loose
    Dry Loose
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.
More info at Avalanche.org

Areas that have been sheltered from the wind are holding very weak loose snow.  We were able to easily trigger sluffs in terrain over 40 degrees yesterday.  Sluffs were relatively low in volume but were running long distances.  With this in mind, it will be important to manage your sluffs today.  The bigger and steeper the terrain, the greater the volume these sluffs will become. Don’t let your sluff catch up with you; turn away from moving snow, let it go past you or move faster than it to manage this problem.

With clear skies and just slightly warmer temperatures in store today, pay attention to steep slopes receiving direct sun.  There is potential for shallow damp loose snow avalanches to release naturally later in the day. 

Weather
Sat, April 13th, 2013

In the past 24 hours the mountains around Eastern Turnagain Arm have received no precipitation.   Winds have been blowing 7mph out of the NW with gusts to 23mph at the Sunburst weather station (3,812′).   Winds were stronger in certain higher elevation locations that were catching the north winds yesterday as we observed in both the Turnagain and Summit Lake areas (see photo below).   Temperatures at Sunburst have averaged 6.8 degrees F.

Summit Wind loading 4-13

Look for today to be very similar to yesterday.   Light to moderate winds, blowing less than 10mph out of the North may help to move around any snow available for transport.   Clear skies will help to heat up sun exposed slopes later in the day.   Temperatures at 1,000′ will climb into the mid to high 20s F.

A ridge of high pressure has established itself over the Bering Sea and is extending into our area.   This will translate to clear skies through the weekend with temperatures rising just slightly over the next few days.   Look for winds out of the north to pick up speed tomorrow.

_________________________________________________________________________________________

Wendy will issue the next advisory tomorrow morning, April 14th.

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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.