Tue, December 25, 2012 Turnagain Pass Avalanche Forecast

Tue, December 25th, 2012

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

4 - High

Below Treeline

Below 1,000'

4 - High

0 - No Rating

1 - Low

2 - Moderate

3 - Considerable

4 - High

5 - Extreme


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

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

Wind has been blowing into the 60s at the ridgetops along with all that new snow. Natural avalanche activity started sometime yesterday and got bigger overnight as the new snow piled up. Despite a taper expected this morning in the storm intensity, the possibility of natural and human triggered avalanches will remain high this morning. With this much snow we can expect large avalanches to run down into valley bottoms, making safe areas difficult to determine even below treeline. The best travel advice today is to stay away from the Kenai peninsula or go to Alyeska.

Avalanche Problem 2

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

Areas below treeline that are less wind affected will still have a huge amount of new snow. All this new weight is sitting on a very weak base from early winter. There is nothing good about this combination… The stress of the new snow will be exceeding the strength of the underlying foundation. Let’s give it time to go through the natural avalanche cycle before we go play in the new snow.

By mid afternoon yesterday the backcountry in Turnagain was already so deep that it was difficult to ski. The snow depth has doubled since then… Again, the best advice is to stay away until the snowpack has time to adjust to this massive new load.

Weather

Tue, December 25th, 2012

24 hour storm totals as of 5am

Turnagain Pass – 24-30 inches snow, 2+ inches of water

Alyeska – 25-36 inches snow, 3+ inches of water

Wind reaching over 60 mph at most ridgetop weather stations.

Temperatures have risen during the storm, with some rain at low elevations. The storm is expected to taper this morning both in wind and precipitation. Tomorrow morning another pulse is expected to hit with more heavy snow and high wind across our region. The Blizzard Warning is canceled, but the storm is not over.

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).

Wendy will issue the next advisory Wednesday morning December 26th.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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