Fri, November 23, 2012 Turnagain Pass Avalanche Forecast

Fri, November 23rd, 2012

Alpine

Above 2,500'

3 - Considerable

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

With little change in the weather, we had yet another natural avalanche release in the heart of Turnagain Pass sometime late on Wednesday, Nov. 21^st , or early yesterday morning. This was on the SW face of Sunburst – photo below and more details HERE. The slide was believed to be triggered by a slight bump in wind that loaded the slope and tipped the balance. The loading was minimal, demonstrating the precariousness of the pack. It is events like this that is keeping us on our toes.

Good travel practices are essential right now. We have seen 5 natural avalanches the past 4 days and heard of 0 human triggered avalanches (the past 4 days). I believe this is attributed to folks managing their terrain with lower slope angles and looking for areas where the snow cover is entirely weak snow (sugar) and lacking a slab. Suspect slopes are those with supportable stiffer snow over weaker hollow snow and are to be avoided. As we have mentioned, a ride down one of these rocky bed surfaces if caught could get ugly. Straying a bit from the established skin track and feeling for collapsing and cracking as one travels is a good way to gain a sense of the snowpack.

The weak snow from October continues to plague us and the past several days of cold and clear weather is not helping to strengthen it. But, what the weather has been doing is actually weakening the strong layer (the slab). If the slab becomes weak enough (through faceting) the snow cover will change back to one layer of loose sugary snow. In this case, the avalanche danger decreases substantially until it gets covered by the next bout of snow and/or wind. This process has already occurred on certain slopes, making them safer than they were one or two weeks ago.

Below treeline, the structure of a slab over weak snow is not present. The pack here consists mostly of 12-24″ of loose weak snow with a crust layer about 8-10″ down from the surface (formed by the rain and wet snow on Nov 2nd).

Weather

Fri, November 23rd, 2012

Two words: clear and cold. The single digit temperatures that have been pooling in our low elevations and parking lots will remain in place for the next several days. The good news is warmer air, in the mid 20’s, sits just above the inversion on the ridgelines. The northerly winds that picked up yesterday have decreased and should blow around 5mph from a northerly direction today. As for snow, there is a chance we may see some flurries fall the middle of next week. Other than that it looks bleak.

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).

Kevin will issue the next advisory Saturday morning, November 24th.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
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

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