Mon, January 14, 2013 Turnagain Pass Avalanche Forecast

Mon, January 14th, 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

Deep Persistent Slabs

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

More info at Avalanche.org

Deep slab avalanches continue to be our greatest concern. This most recent load of snow, while dense, is probably not enough to drastically increase the likelihood of triggering these large and destructive avalanches. The weak layers formed in October and November are now buried 4-10 feet in many areas, and are getting more difficult to impact with the weight of a person or snowmachine.

Areas to avoid today are trigger points in upper elevation starting zones, where those weak layers are only covered by 1-3 feet of slab. If you’re able to hit one of these spots, the potential for avalanches to propagate across large areas remains very high. What this means is that the chances of starting one of these avalanches is low to moderate but the consequences are very high. Human triggered deep slab avalanches in the past two weeks have produced impressive amounts of debris, and still warrant our attention.

Avalanche Problem 2

Storm Slabs

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

With a gradual rise in temps over the past 2 days, we have an “upside down” scenario in the upper layers of the snowpack. Pit tests at treeline yesterday on Tincan revealed this weakness and showed potential for propagation across slopes. AKDOT was also able to trigger many avalanches around Bird Flats and Girdwood in the storm snow yesterday. While the storm snow totals were higher in these areas, the general trend of warming over the past 48 hours is similar in both places. Expect this problem to resolve itself more quickly than the deep slab problem.

Weather

Mon, January 14th, 2013

In the past 24 hours Turnagain pass has received ~8″ of new snow with .8″ water. Winds have been light to moderate out of the East averaging in the teens with gusts to 49 mph. Temps at 1800′ have been around 32 with temps at ridgetops in the mid twenties.
The biggest news in weather is that the forecasted rise in temperature and heavy precip did not come to fruition on Turnagain Pass. The Girdwood Valley has seen almost twice the amount of precip in the past 24 hrs.
Look for precip to taper off today and temps to start gradually dropping with freezing levels descending to sea level by tonight.
The extended outlook calls for a break in precip later today into Tuesday with snowfall returning by midweek. Temps will be significantly cooler through the next 3 days.

_______________________________________

Wendy will issue the next advisory tomorrow morning, January 15th.

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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