Thu, February 06, 2014 Turnagain Pass Avalanche Forecast

Thu, February 6th, 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

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

In terrain above 3,500’, the last storm cycle laid down mostly snow (as opposed to rain). Terrain above this elevation is harboring old wind slabs up to a foot in depth. These slabs are resting on weak interfaces. It is on steep upper elevation leeward slopes where you are most likely to encounter unstable snow today. The likelihood of triggering an old wind slab is on the lower end of the scale but cannot be ruled out.

We got a good observation from the Divide creek area yesterday. A shallow layer of facets is somewhat reactive to pit tests. Same for the well developed facets at the ground. Overall these are only moderate concerns, but should be taken into consideration when out in the backcountry.

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

Slabs 3-6 feet thick are sitting on weak snow near the ground in the upper elevations. It is less likely to trigger a deep slab today in comparison to a more shallow old wind slab or persistent slab. However, the possibility remains for triggering a slab that can pull out snow to the ground. Unlike the persistent (old) wind slab concern, deep slabs have the potential to move large volumes of snow. Avoiding likely trigger points, especially areas where slabs are thinner, will lower the likelihood of triggering a deep slab avalanche today.

This problem is not a concern below 3000 feet where the previously water saturated layers have now frozen into a very strong and stable crust layer.

Additional Concern

Announcement

Announcement

More info at Avalanche.org

In case you’re just tuning in, we have a very thick crust in the forecast area. This “bulletproof” crust exists on all aspects up to 3,500’ in elevation, and is over 2 feet thick in places. Travel in steep terrain warrants extra caution, as arresting a fall is very challenging at this time.

Expect all of these issues to remain until a shift in the weather pattern takes place and surface conditions change.

Weather

Thu, February 6th, 2014

Clear skies, light wind, and average winter temperatures (20s F) have been the weather over the last couple days. This trend will continue through today and transition to something a little different this evening.

The National Weather Service is issuing a Winter Weather Advisory for Friday morning to Saturday morning for blowing snow that may reduce visibility and make travel difficult. This is due to a forecasted 2-6 inches of cold dry snow with moderate to strong wind.

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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