Mon, February 25, 2013 Turnagain Pass Avalanche Forecast

Mon, February 25th, 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

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

In the upper elevations winds have been consistently blowing in the upper teens to low 20s out of the East. Expect to encounter wind slabs up to 18″ in depth today in starting zones. While the new storm snow that fell over the weekend has in general bonded well to old surfaces, the simple act of windloading can and will create areas of unstable snow. Continued winds out of the East today will help to increase the size of these slabs. Be on the lookout for snow that looks smooth, rounded and pillowy. These areas will be most sensitive while the snow is being transported and slabs are forming. While the predominant wind direction is out of the East, localized winds will blow in a variety of directions. With this in mind it is important to recognize wind and loading patterns and stay off of slopes that have been recently loaded.

Avalanche Problem 2

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

A crust that formed prior to the weekend has shown to be a problem in some areas. Yesterday my partner and I found weak snow just below this new crust to be reactive and unstable in the lower elevations. While this is not a widespread problem, it is worth paying attention to, especially if you experience collapsing/whoompfing as we did yesterday.

Deeper weak layers that were reactive in tests and have produced several avalanches over the past two weeks have not shown to be a problem recently. A mid elevation crust (~1,500′-3,000′) with weak snow above, and the old weak snow at the ground have been the two layers we have been tracking. Despite a lack of activity at these layers it is still worth keeping them in mind as they have the potential to re activate in areas where the snowpack is more shallow.

Weather

Mon, February 25th, 2013

Over the past 24 hours the mountains have picked up to 3″ of new snow in the Girdwood Valley, with lesser amounts on Turnagain Pass. Winds have averaged 15 mph out of the East and temps have been in the high teens F at 3,800′ and around 32 F at sea level.

Today we should expect to see light snow showers picking up later in the day as another weak low pressure system moves over the forecast area. Ridgetop winds will blow 20-30 mph out of the East and temps at 1,000′ will be in the mid twenties.

The extended outlook calls for more of the same, as an active weather pattern continues to bring modest amounts of snow to the area.

_____________________________________________________________

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

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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