Sun, January 06, 2013 Turnagain Pass Avalanche Forecast

Sun, January 6th, 2013

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

2 - Moderate

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

Once again our primary concern will be deep slab avalanches. This is simply due to the size and destructive power this type of avalanche can produce. As the weak faceted snow from October and November is getting deeper and deeper in the pack (4-10′) it is easy to focus on what is going on at the surface – today that will be wind slabs. But we can’t forget that lurking below, where obvious signs of instability are minimal to none, there is a weak layer of snow that is struggling to hold the entire snowpack to the slopes. Triggering a deep slab is not something to get mixed up in and can have deadly consequences. The best practice is to use safe travel techniques and stick to lower angle terrain.

The cloudy skies and low visibility yesterday hampered a good look around the mountains and with no reported slides from others, there are no new avalanches to pass on. The most recent activity we know of is from 48 hours ago on Jan. 4^th where two large slides released naturally. The most significant for the Turnagain Pass folk is the class 3 slide on Seattle Ridge. These events should not be forgotten as the weak layer responsible is over a month old and slab is 2 weeks old, hence the persistence issue.

Remember, the only obvious clue as to a deep slab problem is the knowledge weak snow exists near the ground. All other signs of instability such as cracking and collapsing, including recent avalanches, is not a sign the problem has gone away. A guilty until proven innocent situation.

If you’re interested in a little deep slab reading, here is a good article from our friends in Colorado.

Avalanche Problem 2

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 we found a few small pockets with shallow wind slabs (4-8” thick) at treeline. These were quite reactive to a person as they were in the formation stage and fresh. This should be the case again today with a few more inches of snow and wind that will load leeward slopes. Above treeline slabs will be larger (in the 1 foot or more range) and with the underlying weaknesses at the bottom of the pack, it would not be unexpected for a smaller wind slab to step down and trigger a much larger deep slab.

Weather

Sun, January 6th, 2013

The progressive weather pattern we have been in for the past 2 weeks, that has brought us cloudy skies, snow and wind, continues. Yesterday we picked up around 3 € of snow at mid elevations with rain below 800′. Winds blew in the 30’s with gusts to 50mph from the east. Remember we have weather history charts for those interested.

Today should be similar with an additional 2-4 € of snow and rain up to 6-800′. Winds will remain strong out of the east averaging ~30mph with gusts to 50mph on the ridgetops. Temperatures are currently in the mid 20’s above treeline and mid 30’s below and should cool a degree or two through the day.

A larger system moves in this evening that looks to bring around a foot of new snow tonight into Monday with slightly cooler temperatures. A break in the weather Tuesday into Wednesday may bring a welcome shot of sunshine.

John will issue the next advisory on Monday, January 7th.

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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