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Thu, February 7th, 2013 - 7:00AM
Fri, February 8th, 2013 - 7:00AM
Graham Predeger
Avalanche risk The Bottom Line

An active storm will bring the first marked bump in our avalanche danger in two weeks.   The avalanche hazard is CONSISERABLE above tree line and MODERATE below tree line by way of a winter storm moving into the forecast area.   As this storm progresses throughout the day, we can expect stability to decrease while moderate to strong winds actively build fresh and very tender wind slabs.   Natural avalanches will be possible and human triggered avalanches likely in specific terrain.   A BLIZZARD WARNING remains in effect for Portage Valley and eastern Turnagain Arm from 10 AM to 6 PM today.

Special Announcements

We have a few spots open in our non-motorized backcountry observer training day this Saturday, February 9th.   Check our calendar page for more information.   Join the forecasters for a day in the backcountry and learn how to contribute snow and avalanche observations to your local avalanche center.

Thu, February 7th, 2013
Above 2,500'
3 - Considerable
Avalanche risk
2 - Moderate
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. 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

Forecasted 40-55 mph east winds are guaranteed to build very tender and sensitive wind slabs with yesterday’s 4-8” of light powder combined with today’s storm snow.  As you gain in elevation, slabs will be actively forming throughout the day on a variety of bed surfaces including breakable crusts, buried surface hoar (observed on Tuesday in Girdwood and Turnagain) and in the upper elevations older wind slab.

Below tree line where winds are not as intense, avalanche size is likely to be small though human triggered avalanches will be possible.  Slabs will form mostly on a breakable crust at these lower elevations. 

Above tree line expect slabs to form in all the usual places; below ridgelines on west-facing (leeward) slopes and cross-loaded gullies.  With moderate to high winds, slopes tend to load further downhill than one would think, often luring a skier or snowmachiner mid-slope before finding the trigger point.  The likelihood of triggering a slab in terrain greater than 35 degrees today is probable; there is however some uncertainty on just how big an avalanche may be.

As a fresh shot of wind and moisture rolls in today it is worth mentioning that at higher elevations there still exists weak, faceted snow at the bottom of our pack.  Though we have not seen an avalanche fail on this layer in several weeks, deep slab instabilities are notorious for lying dormant for long periods only to suddenly awake and catch us off guard.  At this point, safe travel protocol will be your best bet to avoid this avalanche concern.

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

If you happen to find areas sheltered from the wind today, yesterday’s low-density powder combined with storm snow will create fast-moving loose snow sluffs in steep terrain.  If expected, these loose-snow slides should prove quite manageable.

Thu, February 7th, 2013

Well it looks to be a bonafide storm day in the eastern Turnagain Arm region today.   Expect this system to ramp up throughout the daylight hours bringing 8-16 € of snow (at all elevations!) and 40-55 mph winds from the east.   Temps look to be in the mid to high 20’s at 1000′ and should stay below freezing at sea level.   A BLIZZARD WARNING remains in effect today from 10 AM to 6 PM.

Tomorrow looks to be a break in action before another weather front moves into south-central over the weekend.   This next system looks promising for more wind and precipitation.

Fitz will issue the next advisory tomorrow morning, February 8th.

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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.