Fri, March 29, 2013 Turnagain Pass Avalanche Forecast

Fri, March 29th, 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

Winds over the last 24 hours have been strong enough to move around snow to create sensitive slabs. Yesterday my partner and I observed these slabs starting to build. Other parties reported similar conditions along and near ridge crests and on leeward slopes. These slabs will be most likely to propagate and pick up speed on steep south facing upper elevation starting zones and above cross loaded gullies. If you notice shooting cracks or the snow below your feet or sled feels hollow and you happen to be in steep terrain, back off before you’re moving downhill with the slab. Warmer temps and continued high winds will help to make these slabs be “upside down” and release with ease.

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

While snowfall amounts have been lower than what was forecasted yesterday, there is still enough loose snow in non wind affected areas to warrant attention. Volume of these sluffs should be in the low to medium range. Volume will increase as more snow accumulates through the day. Sluffs will release more easily as temps climb. On steep south facing terrain crusts will allow the snow to move more quickly. These avalanches will be manageable on their own but have the potential to carry people into gullies & trees, and over cliff bands. Choosing terrain that gives you options for escape will be important in dealing with this problem today.

Additional Concern—Cornice Fall
The winds of the past day have also helped to build the size of cornices. Steer clear of these behemoths as they can do significant damage. The largest avalanches that have occurred in the month of March have been the result of cornices dropping.

Weather

Fri, March 29th, 2013

In the past 24 hours the Turnagain Pass SNOTEL has picked up 6″ of new snow with .5″ of water. Winds at the Seattle Ridge weather station at 2,400′ have averaged 30mph out of the SE with gusts to 59mph. Temperatures have averaged 16.5 degrees F at this location. Temperatures have been on the rise since the early morning hours and are currently in the low 20s F.

Today expect continued intermittent snowfall, with 4-7″ of accumulation possible. Winds at ridge tops will average 35-40mph out of the SE with gusts over 50 mph. Temperatures at 1,000′ will be in the low to mid 30 F range.

The extended outlook calls for a continuation of unsettled weather going into the weekend with snowfall amounts remaining relatively light.
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Kevin will issue the next advisory tomorrow morning, March 30th.

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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