Mon, December 16, 2013 Turnagain Pass Avalanche Forecast

Mon, December 16th, 2013

Alpine

Above 2,500'

2 - Moderate

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

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 storm that dropped 12-18” of new snow on Turnagain Pass came down with very little wind and relatively cold temperatures. The rate of loading was slow enough to not create widespread natural activity. Over time this new light density snow has formed into more cohesive slabs. Yesterday we received numerous reports of low volume slab activity around Turnagain Pass. All activity observed and reported yesterday ran on a crust that formed earlier in December.

The crust that exists below this new snow is fairly uniform in its distribution (i.e. is similar on all aspects and elevations). The new snow is also uniform in its distribution. The interface between this crust and new slab has shown poor bonding in many areas. As such, all aspects above and below treeline are harboring soft slabs that will continue to be sensitive to human triggers. Throw in the occasional pocket of buried surface hoar into the mix and it becomes trickier to figure out where the most sensitive areas are. Your best bet for avoiding this problem today is to stick to lower angled terrain.

Graham-Seattle 12-15-13

Soft slabs triggered remotely in steep terrain off of Seattle Ridge. (photo: Wagner)

Avalanche Problem 2

Dry Loose

Dry Loose

Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

More info at Avalanche.org

Loose snow avalanches will begin to come into play a bit more today with cold temperatures helping to weaken the snow surface. Expect sluffs to run slowly and be low volume. Pay attention to sluffs in steeper terrain where terrain traps are present. While the volume will be low the chances for injury will go up if you are knocked over and carried into trees, over rocks or into gullies.

Weather

Mon, December 16th, 2013

The mountains around Eastern Turnagain Arm picked up a trace of new snow in the past 24 hours. Winds have been light out of the Northwest and temperatures have averaged in the single digits F. Ridge top temperatures early this morning are hovering around 0 degrees F.

Clear and cold is in store today as a ridge of high pressure has built into the area. Winds will be light out of the North and Northwest.

Weather conditions will remain similar over the next several days. The next chance for precipitation looks to be late Wednesday into Thursday.

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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