Thu, January 03, 2013 Turnagain Pass Avalanche Forecast

Thu, January 3rd, 2013

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

3 - Considerable

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

Deep Persistent Slabs

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

More info at Avalanche.org

Yesterday a skier on Tincan triggered a large avalanche and fortunately avoided burial. This was a very destructive avalanche, pulling out most of the snowpack on this slope. For info and photos of this avalanche click here, here and here. Stay tuned for more info on this avalanche.

During times of intense precip, like today, the likelihood of triggering deep slabs goes up. As storms subside the likelihood will go down. The high consequences, however, do not change.

The fact remains, and will remain for a long time, that weak layers near the ground are still weak. All it takes is finding a spot where the slab is less deep, i.e. where we can impact the layer more easily, and large destructive avalanches will occur. These trigger points are often very difficult to detect. The usual warning signs of recent avalanches, shooting cracks or whoompfing may not present themselves before it’s too late.

Observations from New Years Eve allowed us to see areas above treeline that have been greatly affected by high winds. Some areas have been scoured to the ground while other areas are holding massive slabs. With such a great variety of slab depths at the upper elevations, the potential to find a trigger point is now greater. The best way to manage this problem today is to avoid terrain that is steep enough to slide.

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

With up to 10 inches of new snow and 50 mph winds forecasted, expect wind deposited new snow to be sensitive to human triggers today. The likelihood of getting wind slabs to release will be higher today than deep slabs. However, the potential for relatively shallow avalanches to step down into deeper layers make this a problem not to be trifled with. Below treeline and in sheltered areas, new storm snow unaffected by winds will also be a problem to look out for.

Weather

Thu, January 3rd, 2013

In the past 24 hours snowfall amounts have been in the 2-3″ range, ridgetop winds have averaged 35 mph out of the East and temps have remained mild, with freezing levels hovering around the 1000′ level.
Snowfall will pick up in intensity this morning and into the daytime hours, with total accumulations of up to 10″ possible during the day. Ridgetop winds will be 50-60 mph out of the SE, and temps at 1000′ will be in the low 30s F.
The general pattern of unsettled weather will continue through the weekend. Look for precip to continue and a gradual cooling trend to set up as we move into next week.

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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