Tue, February 11, 2014 Turnagain Pass Avalanche Forecast

Tue, February 11th, 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

Areas such as Tin Can continue to harbor a weak layer of facets just below the storm snow that was deposited during our very localized storm on Friday February 7^th. The common weak layer in several human triggered avalanches over the weekend has been a thin layer of buried facets resting on the stout rain crust that continues to prove reactive to human triggers. Though not widespread, this buried layer of facets has been popping up across the forecast area with reports of remote triggered avalanches as recent as yesterday. Additional activity includes this snowboarder triggered soft slab in Warm up bowl yesterday (see photo below).

Snowboarder-triggered soft slab in Warm Up Bowl, February 10th.

In terrain above 35 degrees where the snow is cohesive enough to form a slab it will be possible to trigger a soft slab avalanche 12-24” deep. With a known persistent weak layer and slick bed surface, sussing out if a slab exists on the slope where you want to travel will be the key to fun and predictable skiing today. It’s worth noting that the slab does not exist uniformly throughout the mountains and much of the snow from Friday’s storm is still quite loose and does not exhibit slab characteristics. Wind loaded slopes however, (generally with a westerly tilt) will be the more likely areas to find a slab and subsequent avalanche.

Numerous hand pits throughout your travels may be the best test to identify where a cohesive slab exists today.

Sun effect?
Believe it or not the sun has been able to create a crust on southerly slopes. This was seen mainly in the mid and lower elevations again yesterday (2,500′ ish).

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 issue is still of concern in the upper most elevations of our forecasting zone. The likelihood of triggering a full depth avalanche is low but the consequences remain high.

This problem is not a concern below 3000ft 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

We have received some great observations over the past several days in the Turnagain pass area and the variability of this most recent storm (Friday Feb. 7^th) has been quite impressive in terms of snowfall amounts and bonding to the melt-freeze crust from ridge to ridge and valley to valley. With a dozen or more avalanches on Tin Can Saturday and a generally quiet weekend across the valley on Seattle Ridge (and even Sunburst), this is a good reminder that spatial variability exists within the mountains. The information gleaned from this website is only one piece of the puzzle and its imperative that decisions in the backcountry are made based on a litany of information gathered throughout the day in your particular location.

Weather

Tue, February 11th, 2014

Clouds broke up around noon yesterday revealing mostly sunny skies after depositing up to 2 € of low-density snow in the Turnagain Pass region. Winds at the mid and upper elevations also dropped off to the low teens around this time though winds in the lower elevations along Turnagain arm did see an up-tick in the afternoon, predominantly from the west. Temperatures reached as high as 20 degrees during the heat of the day on Seattle ridge, yet it felt much warmer in the direct sun.

Today we can expect a generally mild day in terms of weather. Sunny skies and light variable winds will be in store with temperatures reaching about 20 degrees at 1,000 feet. There will be a possibility for valley fog to roll in come afternoon, as this has been the trend over the last several days in Turnagain pass.

Looking out a few days the National Weather Service seems to have high confidence in a portion of the polar vortex (that has been so burdensome in the lower 48) dipping south across the state and ushering in much colder temperatures. There looks to be at least a chance of snow everyday Wednesday through Saturday, and given the forecasted cold temps any snow will fall as low-density powder, also known as the super-fluff!

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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