Fri, November 25, 2016 Turnagain Pass Avalanche Forecast

Fri, November 25th, 2016

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

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

A widespread layer of surface hoar (formed November 15th/16th) is buried below 10-20” of snow throughout Turnagain Pass on all aspects. If you’ve been reading the advisory all week, you already know that this weak-layer/slab combo has been extremely reactive. Dozens of human triggered and remote triggered avalanches have occurred since November 17th on the popular slopes of Tincan, Sunburst, and Magnum. These avalanches have been on the edge of small to medium in size; just large large enough to bury a person or seriously injure you in a ride.

This is important to keep in mind today and throughout the weekend with more snow heading our way. Today we could see an additional 2-6 inches of new snow and more coming this weekend. The snowpack is still unstable and an additional load will only make the consequences even larger. Maintain a conservative mindset when choosing your route and keep your slope angles gentle. Be on the lookout for obvious signs of instability like blowing snow, shooting cracks and whumphing sounds. Remember larger slopes can produce bigger avalanches. With the holiday weekend ahead there could be more people heading into the backcountry. Be extra aware of other groups above and below you and only expose one person on a slope at a time.

*Yesterday was the first day out of 7 days we haven’t received any reports of human triggered slab avalanches in Turnagain Pass. With time this layer of buried surface hoar is becoming more stubborn, but this also means the slab has the potential to fracture once well onto the slope. This was exactly the case on Wednesday (November 23rd) when two skiers triggered two avalanches on a slope that had been skied multiple times on Sunburst’s Southwest face. One of the skiers reported that both slides broke above them and were “nearly impossible to escape from.”

Sunburst Southwest face. The avalanche on the left was remotely triggered on Tuesday, November 22nd. The avalanche near the ridge occured on November 23rd after the slope had been skied several times.

Avalanche Problem 2

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

There were two glide avalanches reported on November 23rd and other glide cracks have been observed around Turnagain and Summit area. If you see a glide crack give these a wide berth, minimize time spent underneath, and remember these are totally unpredicatable. They are not triggered by humans and are the entire snowpack releasing.

A glide avalanche on Sunburst SW face that released on Wednesday November 23rd. The crack on the right continues to open and widen.

Weather

Fri, November 25th, 2016

Yesterday skies were clear and no precipitation occurred. A temperature inversion kept cooler air (10-15 F) and some fog in the valley floor and ridgetop temps were in the 20’s F. Northwest ridgetop winds were moderate (15-30mph) in the morning deminishing by noon to light Northeast winds.

Overnight Southeast ridgetop winds increased into the 20’s mph and temperatures have been on a steady rise into the 20’s F. Light snowfall started as of 6am at Turnagain Pass.

Today 2-6 inches of new snow may fall the upper elevations. Temperatures are anticipated to remain just below freezing at 1000′ and ridgetop winds are expected to be light from the North. This is the beginning of a several storms tracking through Southcentral Alaska in the next few days. Saturday evening into Sunday expect heavier snowfall and stronger winds.

PRECIPITATION 24-hour data (6am – 6am)

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	22	0	0	17
Summit Lake (1400′)	14	0	0	3
Alyeska Mid (1700′)	21	0	0	3

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	19	variable	6	27
Seattle Ridge (2400′)	22	variable	11	33

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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