Tue, November 26, 2013 Turnagain Pass Avalanche Forecast

Tue, November 26th, 2013

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

1 - Low

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

Persistent Slabs

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

More info at Avalanche.org

The old surface that we were skiing a week ago is the current weak layer, with the November 21st storm snow failing on those loose faceted grains. See this observation for a detailed look at the snowpack structure. Since the storm on Friday we have had 3 decent avalanches reported to us, and keep in mind that few people are skiing south of Anchorage right now. All of these avalanche events are behaving in a similar nature, breaking on the storm interface from November 21st. The storm snow is heavier and denser than the underlying layer of weak faceted snow, making this failure easy to identify in snowpit tests. Reports from a couple days ago were identifying failure on isolation or with very light force.

The picture below is actually from the Summit Lake area, but shows a similar problem farther south on the Kenai. See this observation for another picture from that reported avalanche.

We expect this kind of avalanche potential to stay for a little while longer. Time, warm temperatures, and continued storm cycles will eventually fix the problem. Until then, caution is warranted when deciding where to go right now. Also keep in mind that the snowpack is shallow. Rocks and trees are barely covered, if at all.

Weather

Tue, November 26th, 2013

There is no new snow in the last 24 hours. Temperatures are in the high 20s. Wind is light.

The National Weather Service continues to have light snowfall in the forecast. 1-3 inches of snow is possible today as a weak surface low enters Prince William Sound this morning.

Temperatures will stay near freezing in the mountains and perhaps rising above freezing near sea level. Wind will stay light and variable, 10-20 mph.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/13/24	Turnagain	Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South	H Thamm
05/13/24	Turnagain	Observation: Turnagain Pass non-motorized side	Amy Holman
05/12/24	Turnagain	Observation: Warm up Bowl	Tony Naciuk
05/07/24	Turnagain	Observation: Turnagain Pass Wet Slabs	A S
04/29/24	Turnagain	Avalanche: Turnagain aerial obs	Tully Hamer
04/27/24	Turnagain	Observation: Johnson Pass	Noah Mery
04/23/24	Turnagain	Observation: Turnagain Sunny Side	Travis SMITH
04/21/24	Turnagain	Observation: Bertha Creek	Anonymous
04/20/24	Turnagain	Avalanche: Spokane Creek	Schauer/ Mailly Forecaster
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster

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