Sat, February 06, 2016 Turnagain Pass Avalanche Forecast

Sat, February 6th, 2016

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

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

Storm Slabs

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Today could be one of those days where someone could easily be caught in an avalanche: It will be our first chance for a break in cloud cover after a 4 day storm and it’s Saturday. The big concern centers around 2-3′ of new snow, which fell between Tuesday and Friday, that sits on a layer of weak older snow. This weak old snow was last weekend’s surface, which became loose and faceted along with a layer of surface hoar on top. Not only that, at the mid-elevations, between 2,000 and 3,000′, a crust exists below the weak snow (see photo below). What this all boils down to is that the new snow may not stabilize very quickly after this storm and people could trigger large and dangerous avalanches through the weekend. Things to keep in mind with this type of snowpack:

1) This unstable ‘set-up’ is one we have not seen this year

2) Triggering an avalanche remotely, from the side, top or below a slope is possible

3) The snowpack between 2,000′ and 3,000′ (where the weak snow/crust combination exists under the new snow) could be more unstable that the higher elevations. Crusts can inhibit stability and contribute to the possibility for remote triggers.

4) With little ground truth information at this point, very cautions terrain selection is required.

5) Sticking to slopes less than 30 degrees – with nothing steeper above you – to give the snowpack time to adjust is a great way to have a safe weekend in the backcountry.

The photo below shows the new snow at 2,000′. At this elevation the snow was very warm and dense; the rain snow line was just below this and lighter and deeper snow existed just above this.

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

The glide avalanche cycle continues…. Another glide crack released into a full-blown avalanche sometime late on Thursday or early Friday morning. These cracks are clearly still active and avalanching. Again, this is not the type of avalanche that can be triggered, but instead release spontaneously on their own. Just one more reason to avoid being under steep slopes today.

Photo: Glide avalanche on the Southeast face of Seattle Ridge, between the motorized lot and the motorized up-track.

Additional Concern

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

With the warm and sticky nature of the new snow, cornices are likely to have grown even larger (they are already behemoths…) and be on the verge of collapse. These are not only hazards in themselves, but are also likely to trigger large avalanches below.

Weather

Sat, February 6th, 2016

Yesterday we saw the tail end of the storm cycle move out with light snowfall adding roughly 1-3″ of new snow. 1″ fell at the Center Ridge SNOTEL at 1,900′ while 3″ fell in Girdwood Valley at the Alyeska Mid station. Winds died down as well with averages ~15mph from a generally East direction. Temperatures were warm (low 30’s at 1,000′) with a rain/snow line fluctuating between 1,000′ and 1,200′.

This morning we are seeing a quick pulse of moisture, increasing cloud cover and increasing Easterly winds move though. This should exit the region by mid-day and skies may break up if we are lucky. We may pick up another 1-3″ of snow with a rain/snow line ~500′ this morning. Winds are expected to be in the 15-25mph range from the East on the ridgetops. Temperatures look to hover in the upper 20’s at 1,000′ and near 20F at 4,000′.

For Sunday, another band of wind and snow looks to move in. We should see some breaks in this stormy pattern this week hover, so stay tuned.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	28	1	0.1	110
Summit Lake (1400′)	27	1	0.1	32
Alyeska Mid (1700′)	30	3	0.33	87

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	NE	15	46
Seattle Ridge (2400′)	25	–	–	–

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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