Fri, March 21, 2014 Turnagain Pass Avalanche Forecast

Fri, March 21st, 2014

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

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

Almost a full week has passed now since any reports of major avalanche activity in the backcountry, and with people pushing into bigger terrain without incident yesterday this points toward a stabilizing snowpack.

We do know however that weak snow still exists below the March 10-14^th storm cycle that produced a slab up to 5’ deep. It is becoming increasingly more difficult to upset this weak layer but if affected the resulting avalanche will be large and potentially un-survivable. Tracks on a slope do not correlate to stability when dealing with a deep slab avalanche problem. Shallow spots in a slab are likely areas to trigger an avalanche up to 5’ in depth today. These may be difficult to recognize but some clues to a shallow, tapering slab include areas near rock or tree outcroppings or directly adjacent to wind-stripped terrain.

This photo from the Crested Butte Avalanche Center is a good illustration of how a slab tapers.

Likely trigger spot for this avalanche would be near the lower right corner of the photo where the

slab is thin and a human is more likely to affect the weak layer.

If your tolerance for risk is taking you into bigger, steeper terrain today it is fundamental that you and your group exercise safe backcountry travel protocol. This includes communicating travel plans, escape routes and islands of safety. Expose only one person at a time on a slope and re-group in safe areas well away from run-out zones.

Avalanche Problem 2

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

Strong solar radiation late in the day continues to push cornices toward their natural breaking point. Add a skier or snowmachiner on a ridge in close proximity to one of these backcountry bombs and cornice failure will be possible. Your best bet to mitigate this problem today and everyday is to give cornices a very wide berth when travelling on ridges and limit your exposure when travelling beneath.

Weather

Fri, March 21st, 2014

The first day of Spring yesterday did not disappoint with sunny skies, temperatures reaching into the mid-30’s at 1,000′ and light to moderate winds out of the east.

Today we can expect partly cloudy skies by this afternoon, winds out of the east in the 10-25mph range and temperatures again warming into the mid to high 30’s by the heat of the day. Looking into the weekend an upper level ridge will persist over the mainland, keeping southcentral Alaska mostly sunny and completely dry at least through early next week.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
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

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