Sun, November 18, 2012 Turnagain Pass Avalanche Forecast

Sun, November 18th, 2012

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

2 - Moderate

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 Wednesday’s 6 inches of snow settled to ~4 inches the snow surface was quite inviting yesterday. Several people were out enjoying this on lower angle slopes and tracked up areas such as the front side of Tincan ridge. Reports from yesterday were in the form of whoomphing and collapsing but we did not hear of any avalanche activity. That being said, very few people have ventured past the easier accessed lower angle terrain, or short steeper slopes (several of which have already avalanched).

This “persistent avalanche” problem is guilty until proven innocent. We know the snowpack structure is poor. We know there are, at the very least, scattered slopes hanging in the balance waiting for a trigger. Yet, there is uncertainty as to how widespread these touchy slopes are. With a few more inches of snow possible today, warmer temperatures and increased wind, this will only add to the problem.

We went up yesterday to take a look at the avalanche that was remotely triggered from ~200′ away two days ago, Friday (11/16). This was on a steep slope on the southwest face of Sunburst and proves how unstable the pack is. More details HERE and HERE.

One of the most concerning aspects to our avalanche conditions right now are that the obvious clues so prevalent the past couple weeks are not nearly as obvious anymore – but the avalanche potential remains similar. This means it can be easier to be lured onto a slope before it breaks. The only clue may be the presence of a slab over a weak layer (if one looks for it), but recent avalanches, cracking or collapsing may not be observed. Furthermore, a slope may or may not slide, but if it does, the ride will likely be rocky and unpleasant. These are good things to keep in mind when the ‘go’ – ‘no go’ question comes up.

Below treeline the snowpack is a combination of crusts, low density snow and moist facets. This accompanied with the lack of a slab, mainly due to minimal wind loading, has kept avalanche activity at bay.

Avalanche Problem 2

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

Fresh wind slabs may be formed today if the expected 2-4″ of snow with 15mph, gusts to 30, ridgetop easterly wind verifies. With the existing loose snow surface there is plenty of snow available for transport if we only see the wind. Any fresh slabs are likely to be shallow but touchy.

Weather

Sun, November 18th, 2012

Mostly cloudy skies with temperatures plummeting into the single digits and low teens greeted backcounty travelers yesterday. A trace of snow fell throughout the day with very light northerly ridgetop winds.

Temperatures have rebounded this morning to ~20F on the ridgetops but are still inverted with mid teens in the lower elevations. Winds have bumped up slightly and are forecast to blow 15mph with gusts to 30mph from the east. Cloudy and obscured skies should keep visibility limited again today and there in a chance for 2-4″ of snow. This unfortunately looks to be our last shot of precip for the next several days to a week. Clear and cold conditions look to set in Monday through Thanksgiving.

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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).

Kevin will issue the next advisory Tuesday, November 20th.

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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