Sat, December 01, 2012 Turnagain Pass Avalanche Forecast

Sat, December 1st, 2012

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

Pockets of unstable snow may still be present in wind loaded areas at high elevation. Most slopes where people are skiing have weakened to the point where the entire snowpack is one big weak faceted layer. This actually makes the backcountry safer now than it was a couple weeks ago, except that it’s easier to tag rocks on the way down…

The analogy I’ve come up with compares the snowpack to engineering a building. We all know that we can construct a tall stable skyscraper that can withstand significant stresses from wind and earthquakes. The strength of that building relies fundamentally on the strength of the foundation. If you build a skyscraper on top of a weak foundation, failure and catastrophic collapse is likely. If you make a smaller and lighter building, the foundation doesn’t need to be as strong to support the structure above. Our snowpack right now is a tent, without any foundation. The tent itself is inherently weak, but collapse of that tent isn’t nearly as catastrophic as a collapse of the skyscraper. In fact, the tent will bend when stressed before it breaks and collapses. The big problem will happen when the next snow storm (new construction) gets placed on top of the tent. How much weight can that tent support?

Why did the snowpack turn into one big weak layer? Check out Wendy’s temperature profile graph HERE. It’s all about weeks of high temperature gradients caused by shallow snow (only 22 inches in November) and cold air temperatures.

temperature gradient

Weather

Sat, December 1st, 2012

The forecasted high wind over the last couple days has not affected the Turnagain Pass region. Clear, sunny, and cold weather will continue today and through the weekend. A temperature inversion is still present, making higher elevations warmer than the valleys below. Portage this morning is reading -18 degrees, while Sunburst at 3812 ft is reading 15 above.

A pattern change is beginning to show up in the extended forecast. A chance of snow is predicted for next Wednesday!

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 Sunday morning, December 2nd.

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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