Sat, December 28, 2013 Turnagain Pass Avalanche Forecast

Sat, December 28th, 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

While there have only been small amounts of occasional snowfall in the month of December, we continue to observe lingering instabilities in our snowpack. Collapsing has been occurring at all elevations for several weeks now. Snowpit results have shown that the potential still exists for skiers and snowmachiners to trigger avalanches in steep upper elevation terrain. This was the case in a skier triggered avalanche that occurred on December 26 (see photo below). Strong winds that cranked on December 23rd helped to create dense slabs that are sitting on weak snow in upper elevation starting zones. Avalanches of late have been sliding on weak snow just above a crust that was formed in early December.

It will be important to continue to treat steep slopes over 40 degrees with suspicion today.

Photo of a skier triggered slab avalanche that occured on December 26th. No one was injured in this avalanche. (See write up HERE)

Superbowl Av 12-26

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

3-5” of new snow overnight combined with moderate to strong winds out of the East have created shallow pockets of wind slab in the higher elevations. While these slabs will be relatively small, they will be sensitive to the weight of a person or snowmachine. It is more likely to trigger a newly formed pocket of windslab compared to a deeper, older slab today. However, the potential exists for these smaller avalanches to trigger layers deeper in the snowpack. This 1-2 combo of fresh wind slabs and persistent slabs will make it critical to avoid steep starting zones in the higher elevations today.

Weather

Sat, December 28th, 2013

In the past 24 hour the mountains around Eastern Turnagain Arm have picked up 3-5 € of new snow with .2-.3 inches of water. Winds have increased overnight and have averaged 26 mph out of the East since 10pm at the Sunburst weather station. Temperatures have been on the rise as well with Seattle Ridge reading 25 F and Sunburst at 23 F at 6am.

Temperatures will continue to rise today into the upper 20s to low 30s F. Snow showers in the higher elevations will lay down another 1-2 € of snow today. Light rain and freezing rain will fall between sea level and 1,000′. Precipitation will taper off by early afternoon. Ridegtop winds will be out of the East and Southeast at 25-30mph.

The extended outlook is calling for generally dry conditions and mild temperatures over the next several days.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
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

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