Fri, December 09, 2016 Turnagain Pass Avalanche Forecast

Fri, December 9th, 2016

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

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

The snowpack in and around Turnagain Pass is tired, stiff and needs a good re-fresh. A little snow did fall last night, a trace in some places with 1-2″ in others. With a sunny day ahead, keep in mind that we are still concerned about a weak layer 1-2′ below the surface. This is the notorious Nov 16th buried surface hoar (image below). Although we have not seen an avalanche release in this layer for almost a week, there are many slopes away from the ‘popular’ zones that have yet to be tested. These are the areas most suspect.

The good news is, with time triggering an avalanche becomes less and less likely. During the past couple weeks the slab above the weak layer has been ‘faceting‘ away with the cold temperatures. This process turns the slab into loose unconsolidated snow and removes it from the equation; a ‘slab’ is a necessary ingredient for a slab avalanche. The other side of the coin is where the winds have formed new slabs over the weak layer. These are the areas to be most concerned about and look for if you head into the more remote zones. To be clear, we know that most of the high traffic slopes folks have been skiing/riding avalanched weeks ago and have been filled back in, this is why those slopes are generally stable. A tricky situation when heading for fresh lines in the back bowls!

Photo: The notorious Nov 16 buried surface hoar found in Seattle Creek drainage yesterday where an old wind slab remained. The steeper slopes above harbored loose faceted snow (no slab) as mentioned above.

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

There is a significant amount of wind affected snow out in the mountains and on our favorite slopes. Ridgelines sport wind slabs, wind crusts, scoured areas that are covered by an inch or two of fluffy new snow. That said, there are still many pockets of sheltered soft settled powder that can be found.

Watch for fresh shallow wind drifted snow today. We saw drifts along Seattle Ridge yesterday and although they were touchy, they were too small to affect a person. In areas with more snow and wind, the slabs could be large enough to knock you off your feet. The most concerning aspect is getting on a wind slab that breaks deeper in the pack in the buried surface hoar. Older wind slabs are stubborn but a person could still pop one out on steep rocky terrain where slabs have no support from below.

Photo: Wind affected snow on Seattle Ridge.

Weather

Fri, December 9th, 2016

Mostly cloudy and obscured skies filled the region yesterday. Temperatures remain civilized and in the 20’s F at most locations. Winds were gusty from the North along the ridgelines yesterday, averaging 5-10mph with gusts to 25mph. No precipitation.

Overnight, a trace to an inch of very light snow has fallen. Ridgetop winds quieted down and were light with stronger gusts from a Northerly direction. Clouds are moving out this morning and skies are clearing with chances for more snow leaving with them.

A ‘blocking’ high pressure will continue to dominate Alaska’s weather and clear skies with little to no chance for precipitation is forecast for the weekend and into Monday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	23	trace	0	19
Summit Lake (1400′)	20	0	0	4
Alyeska Mid (1700′)	24	0	0.02	11

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	NE	9	25
Seattle Ridge (2400′)	23	Rimed sensors	Rimed sensors	Rimed sensors

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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