Fri, January 25, 2013 Turnagain Pass Avalanche Forecast

Fri, January 25th, 2013

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

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

Look for older wind slabs to be lingering in pockets above treeline today. Light to moderate winds will blow around a few inches of light density snow to also form new shallow wind slabs today. Yesterday my partner and I observed one small human triggered avalanche and one naturally triggered avalanche on the south side of Tincan ridge. The larger of these avalanches was big enough to injure or bury a person. While most of these wind slabs are isolated in their distribution, they can cause problems for people venturing into steep starting zones and above terrain traps such as cliffs, trees and gullies. Wind slabs can be detected by their look and feel; snow that looks smooth and rounded or feels hollow should be avoided.

Avalanche Problem 2

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

The deep slab problem continues to plague us. While the likelihood of triggering an avalanche in old layers of snow at the base of the snowpack is low, the possibility remains. It has been 12 days since a deep slab avalanche has been reported in the backcountry. What is more important to remember is that the consequences of one of these avalanches are high for a person. The volume of these avalanches are typically enough to cause significant damage. We have been fortunate this season in two instances where people triggered very large avalanches in which no one was injured, buried or killed. Continuing to treat large steep open terrain with respect will help to avoid encountering this problem today.

Weather

Fri, January 25th, 2013

The mountains around Eastern Turnagain Arm have picked up a trace of new snow overnight. Winds have been light out of the West. Freezing level has dropped down to sea level and ridgetop temps have averaged in the low 20s F.

Temperatures will be on the decrease through the day reaching the single digits by tonight. Winds will be out of the West averaging 10 mph with gusts to 25 mph. There is a slight chance of continued precip today, with accumulations of up to 1″. Any snowfall should taper off by midday.

Expect clear and cold weather this weekend, with temps remaining in the single digits at ridgetops . The next chance for snow around Turnagain Arm looks to be on Monday.

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Kevin will issue the next advisory tomorrow morning, January 26th.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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