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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, January 1st, 2013 - 7:00AM
Expires
Wed, January 2nd, 2013 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

BOTTOM LINE
A quick hitting storm over the Turnagain Pass region currently will keep our avalanche danger at HIGH today. Additional snow and wind will continue to stress the snowpack throughout the day and natural avalanches are likely. Human triggered avalanches will be very likely and it is recommended to steer clear of avalanche terrain today.

Special Announcements

The AK DOT will be conducting avalanche hazard reduction work today at 1100 on the Seward Highway near milepost 99. See 511.alaska.gov for more information.

Tue, January 1st, 2013
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
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

Happy New Year! Well, the holiday season has not disappointed. In the past week we have more than doubled our snowpack and in some areas tripled it! But, the action is not over. We will welcome in 2013 with yet another storm. This one should be quick hitting but will add another couple feet to our deepening pack.

With current snowfall rates at 1-2 inches per hour this morning we can expect all the usual storm snow problems. These are:

Wind slabs – slab avalanches formed in areas where the winds are loading slopes.
Storm slabs  – slab avalanches in areas without wind that occur before the new snow has time to bond with itself.
Sluffing – loose snow avalanches on steep slopes where the new snow lacks cohesion.

The new slabs formed today will be around 1 1/2 to 2 ft deep and likely quite touchy. At elevations below 2500′ there is a crust formed by the rain on snow from Dec 30th that will act as a bed surface under the new snow. Slides triggered at these lower elevations could run quite far. Getting tangled up in one of these could quickly ruin your day. Staying out of avalanche terrain is still your best bet for getting back to the car safely.

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

The above concerns are all issues dealing with the storm snow and the top layers of the snowapck – but we cannot forget about what is lurking below – the unmanageable and unsurvivable deep slab problem. We continue to have a VERY WEAK foundation to our snowpack and we saw quite a bit of evidence for this yesterday. A quick break in the clouds allowed a look at the recent avalanche activity around the Pass from the past several days. Unfortunately we were not able to see all the popular haunts but HERE is a run-down of what we were able to get a peek at.

Most of the avalanches seen the past week have failed in the weak snow at the bottom of the pack. The slab on top is still around 4-6′ thick in most places and becoming more dense. The slab is also showing signs of getting harder to trigger which is setting us up for a tricky and deadly combination. Meaning, the likelihood of triggering is decreasing but if one of these pulls out, has the potential to be large and dangerous.

Weather
Tue, January 1st, 2013

We have an intense and quick hitting storm over us this morning. Several weather stations in the Turnagain Pass area are not reporting, but looking at the Girdwood Valley and Alyeska stations we are seeing ridgetop winds in the 30-40mph range (these could easily be stronger around the pass). Temperatures are beginning to cool slightly from the upper 30’s at sea level to the mid 30’s and the upper 20’s on the ridges to the mid 20’s Fahrenheit. Precipitation has begun in earnest with 10 € of snow as of 6am this morning. The rain/snow line is hovering at sea level where it should remain. We should see another 8-12 € of snow through today. Snow showers should taper off later today.


Kevin will issue the next advisory on Wednesday morning, January 2nd.

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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.