Thu, December 11, 2014 Turnagain Pass Avalanche Forecast

Thu, December 11th, 2014

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

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

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

Yesterday my partner and I found generally stable snow in the higher elevations. We found evidence of extensive avalanche activity that had occurred during and immediately after the most recent storm on Tuesday Dec 9th. Looking under the snow surface showed us mostly strong snow with one exception. We were able to see some propagation potential along a weak layer 18″ below the surface. Because of this result and only minimal information since the storm, it will be wise to treat steep upper elevation slopes with a healthy dose of respect. While the weak layer in question in our snowpit is one that typically stabilizes quickly, I’m not ready to jump into this type of terrain without gathering more information from below the surface. The general trend today will continue to be towards better stability. The likelihood of triggering an avalanche is on the low end of the scale, BUT there are stiff older wind slabs that are sitting on weaker snow. These older wind slabs will be difficult to recognize, as they are blanketed by low density powder.

Venturing into steeper terrain in the upper elevations will require advanced snowpack assessment skills and the ability to detect old wind slabs hiding underneath 8-10″ of light powder. You can also hedge your bets by sticking to terrain 35 degrees or less in the alpine today.

As mentioned above, early season hazards and a stout & slick rain crust in the mid elevations are legitimate concerns and require careful travel in order to avoid injury.

Additional Concern

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

Yesterday we observed one glide avalanche on the East face of Pyramid that had moved 10-20 feet downhill over the past day. While glide avalanches are not a widespread issue currently, it is worth keeping them in mind. Both Eddies and Tincan have numerous older glide cracks that have not moved over the past couple of weeks. The nature of glide avalanches makes it very difficult to know when they might release. With this in mind, it is best to steer clear of glide cracks and to keep track of where they are.

Weather

Thu, December 11th, 2014

Earlier this week rain, snow, warm temps and moderate winds created unstable conditions throughout the area. Since Tuesday Dec 9th, the weather has quieted down and allowed the snowpack to adjust.

Temperatures over the last 24 hours have cooled into the low 20s F. Ridgetop winds have been light and there has been no new precipitation.

Today expect a continuation of this quiet weather. Skies will be mostly clear with some fog in the valleys. Temperatures will be in the low 30s F at 1,000′ and in the mid 20s F at ridgetop levels. Winds will be light out of the North at 5-15 mph. No new precipitation will fall today.

The extended outlook is showing a chance for snow and possibly rain at the lower elevations as we head into the weekend.

PRECIPITATION 24-hour data (6am – 6am)

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	29	0	0	18
Summit Lake (1400′)	22	0	0	4
Alyeska Mid (1700′)	29	0	0	11.8

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	WNW	6	18
Seattle Ridge (2400′)	28	var	8	23

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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