Mon, March 25, 2013 Turnagain Pass Avalanche Forecast

Mon, March 25th, 2013

Alpine

Above 2,500'

3 - Considerable

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

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

In areas unaffected by wind expect to encounter enough light density snow for riders and skiers to create small to medium sized loose snow avalanches. The only reactive snow we were able to find yesterday was a few inches of this light density loose snow. In terrain over 40 degrees this surface snow slid readily in the form of sluffs and was low in volume and fast moving. Expect more of the same behavior today with volumes increasing as the snow accumulates. Human triggered sluffing has the potential to carry people into and over terrain traps. Choose your terrain with this in mind today.

Storm Snow

New snow in the form of slabs will also be a concern. Expect slabs up to 18″ in depth to be most sensitive on steep south facing terrain today.

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

Look for wind slabs to build today in the upper elevations on west and south aspects. These slabs will be most sensitive on steep south facing terrain where a stout crust lurks beneath the surface and will provide for a good sliding surface. We have had several reports of skier triggered avalanches mainly on south aspects over the weekend. This setup of new snow bonding poorly to crusts primarily exists on terrain over 35 degrees.

Additional Concerns

Persistent Slab
Old wind slabs, formed by strong winds of last Tuesday are lingering below a fresh coating of snow. These slabs are sitting on weak snow, are somewhat random in their distribution, and concealed by 2-8″ of new snow. Because of this they are hard to detect. Staying off of steep terrain (>40 degrees) will help to minimize your chances of finding one of these isolated pockets of slab.

Cornices
The most destructive avalanches we have seen over the past three weeks have been the result of large cornice falls. Minimize your time on terrain with cornices sitting above and approach ridgecrests with caution.

Weather

Mon, March 25th, 2013

In the past 24 hours the mountains around Eastern Turnagain Arm on average have picked up ~6″ of new snow with .6″ of water. Temperatures at the Seattle Ridge station at 2,400′ averaged 22.5 F. Winds there have averaged 10 mph out of the ESE with gusts to 22mph.

Light snow continues to fall in the area and should continue through the evening hours with 6-10″ expected. The peak intensity for snowfall will occur in the morning hours today. Winds will pick back up later in the day and average 15-25mph out of the E. Temperatures at 1,000′ will stay in the high teens to low 20s F today.

The extended outlook calls for clearing on Tuesday with a return to an active (snowy) weather pattern for the second half of the week.

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Wendy will issue the next advisory tomorrow morning, March 26th.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster

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