Sun, November 27, 2016 Turnagain Pass Avalanche Forecast

Sun, November 27th, 2016

Alpine

Above 2,500'

2 - Moderate

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. Dangerous avalanche conditions.	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

Over the last week the alarms have sounded due to a widespread layer of buried surface hoar sitting below 1-2 feet of snow. Observers continue to find this layer on all aspects and elevations throughout Turnagain Pass. Up until a few days ago human triggered and remote triggered avalanches were happening daily with a couple dozen avalanches reported over a 7-day period. These avalanches have been small to medium in size; just large enough to bury a person or seriously injure you in a ride. With time this layer has been adjusting to its load and becoming less reactive and harder to trigger. Last nights snowfall, about 4 inches, arrived after winds calmed down and was just enough to cover up recent avalanche activity. Don’t forget buried surface hoar is a persistent weak layer and human triggered avalanche are still possible. This layer has not gone away and should be a major factor in slope choice today. Larger and/or steeper, more wind-loaded slopes that haven’t been ridden still have the potential to avalanche and could fracture once well onto the slope. Be aware of the consequences below you and keep an eye out for recent wind loading, shooting cracks and whumphing sounds. Practice safe travel techniques like regrouping in safe zones and only expose one person at a time in avalanche terrain. This can be challanging to practice in crowded areas, thus be extra aware of other groups who may be traveling above or below you.

A view of avalanche activity on the popular Sunburst SW face. Photo taken Novemeber 24th before new snow from last night covered it up.

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 numerous shooting cracks were observed near Taylor Pass and Sunburst Weather Station, where moderate winds were activily loading Western aspects. Triggering a small wind slab up to 6” thick is possible in steep leeward terrain near ridgetops. Be aware of supportable and hollow sounding snow hidden below the four inches of new snow that fell overnight. Avoid steep slopes if you experience shooting cracks.

Several 10-20′ shooting cracks were observed yesterday near Taylor Pass

Additional Concern

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

Several glide avalanches have released this week including one observed yesterday morning on the West face of Pyramid. Several glide cracks have been noted in popular terrain like Tincan’s Common bowl and the SW face of Sunburst. If you see glide cracks give these a wide berth, minimize time spent underneath, and remember these are totally unpredictable. They are not triggered by humans and are the entire snowpack releasing.

Weather

Sun, November 27th, 2016

Yesterday morning about an inch of new snow dusted Turnagain Pass and a trace was noted in Girdwood. Skies were overcast becoming obscured in the afternoon. Easterly ridgetop winds were moderate (15-25mph) becoming light by the evening. Temperatures were on the rise all day, teens F to mid 20F’s.

Overnight 4 inches of new snow fell in Turnagain Pass and only an inch in Girdwood. Temperatures remained just below freezing and winds were light from the Northeast.

There is a chance for a few more inches of snow today. Ridgetop winds are expected to remain light and variable and temperatures should be in the mid 20F’s.

Cooler temperatures and clear skies are expected tomorrow evening through Wednesday with another chance for snow near the end of the week.

***Sunburst Weather Station has not recording weather data since Nov.25th. We are currently assessing and hope to get it repaired soon.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	24	4	.4	20
Summit Lake (1400′)	23	trace	.1	2
Alyeska Mid (1700′)	26	1	.11	4

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	n/a***	n/a***	n/a***	n/a***
Seattle Ridge (2400′)	21	SE/variable	9	26

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
11/16/23	Turnagain	Observation: Tincan Common	William Finley
11/14/23	Turnagain	Observation: Sunburst/Magnum	Adrian Beebee
11/14/23	Turnagain	Observation: Seattle Ridge	Schauer/ Creighton/ Ellis Forecaster
11/13/23	Turnagain	Avalanche: Tincan Trees	Eeva Latosuo
11/12/23	Turnagain	Observation: Sunburst	Schauer/ Creighton/ Nave Forecaster
11/12/23	Turnagain	Avalanche: Goldpan – avalanche	Mike Records
11/11/23	Turnagain	Observation: Tincan Common	Andy Moderow
11/11/23	Turnagain	Observation: Taylor Pass – Sunburst	Wadsworth / Stwertka
11/10/23	Turnagain	Observation: Tincan	Andrew Schauer Forecaster
11/10/23	Turnagain	Observation: Tincan Trees	Michael Kerst

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