Fri, December 07, 2012 Turnagain Pass Avalanche Forecast

Fri, December 7th, 2012

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

1 - Low

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

Much of our snow cover from the valley bottom to ridge tops consists of weak, unconsolidated facets in one form or another. This is the type of snow you can’t make a snowball out of to save your life. You may be able to find pockets of more consolidated snow (wind slabs) on the lee sides of ridges and gullies above treeline, but these too have a foundation of weak facets creating a very poor snowpack structure. It should be quite obvious today if you venture onto a slab as it’ll have a hollow, supportive feel to it. This surface will feel very different from the last several thousand feet of “sugar snow” you just ski-toured up through. These wind slab pockets are the primary concern today and triggering one will likely result in a full depth avalanche running to the valley floor. With a shallow, faceted snowpack consequences of triggering one of these wind slabs may leave you broken and battered if caught.

It’ll be important today to understand and come to grips with what our seasonal snowpack looks like to date as this weekend looks to be ushering in our first real winter storm of the season. What snow we have on the ground now will soon be buried and act as a foundation for the rest of the season. Expect our avalanche problems and associated danger rating to change with this impending storm.

Weather

Fri, December 7th, 2012

A change in our weather pattern of the last several weeks has begun as the cold arctic air mass that has dominated the south central region begins to break down. We still have a temperature inversion between sea level (0 degrees in Portage) and 3800′ (15 degrees at Sunburst weather station) but expect this to break down by tomorrow morning as well. Today will be a transition day where we can expect ridgetop winds to shift from a west-northwest direction to more east-southeast as a low pressure system in the gulf builds in strength and enters our forecast area late tonight or Saturday morning. Cloud cover in the Turnagain pass region will build today with this approaching front with a few flurries possible by this afternoon.

The bulk of this approaching storm will impact our area Saturday afternoon through Sunday. The eastern Kenai Peninsula looks to be favored with models suggesting 12-24 € of snow in localized areas (1-2 € of water equivalent). Expect blizzard conditions all day Saturday as winds associated with this storm are forecast to be 30-45mph from the east, likely higher at ridge top locations.

This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).

Kevin will issue the next advisory Saturday morning, December 8th.

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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