Wed, December 26, 2012 Turnagain Pass Avalanche Forecast

Wed, December 26th, 2012

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

4 - High

Below Treeline

Below 1,000'

4 - High

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

The strong easterly winds that accompanied the Christmas storm have died down slightly overnight but will be on the rise through the day today as another system is headed our way this evening. We have little information for above treeline and areas receiving wind due to low visibility and dangerous avalanche conditions but we can expect a good natural avalanche cycle occurred during the past 36 hours and will ramp up again this evening and into tomorrow with additional snow and wind.

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 the significant round of snowfall in the past two days, we have given our early season weak snowpack a good shock to the system. It was no surprise to see widespread avalanche activity yesterday. All the new snow has bonded well to itself but the problem is it is sitting on varying layers of weak faceted snow that will keep it from bonding to the mountain sides. This means avalanches are failing below the new snow making them 3-4′ deep and deeper in windloaded areas – slabs this thick are unmanageable. Observations from below treeline yesterday give a sense of this problem. As the new snow settles with the warming temperatures today the pack will shift from mostly unconsolidated new snow to a denser slab which will add to the already unstable situation. It is great to see so much new snow (a more than doubling of the pack) but patience will be the key to staying safe in the backcountry.

Weather

Wed, December 26th, 2012

It has been an extra white Christmas for the Eastern Turnagain Arm with between 3 and 4 feet of snow falling since the morning of the 24^th. Yesterday, Turnagain Pass saw an additional foot of accumulation with storm totals around the area listed below. As this system exits to the north this morning another one is right on its heels and will usher in warmer wet conditions for this afternoon through Thursday evening. Snowfall amounts look to be in the 10-16″ range.

Total snow accumulation beginning early morning on the 24^th:

Girdwood Valley €“ ~45 € snow with 4.5 € of water equivalent
Turnagain Pass €“ ~35 € snow with 3.4 € of water equivalent
Summit lake €“ ~8 € snow with 0.8 € water equivalent

Snow densities have averaged around 10% region wide, this next storm is warmer and should put down higher density snow along with rain or a rain/snow mix at sea level. Winds have died down overnight (E at 20mph gusting 40mph) but are forecast to increase again through the day (E in the 50-60mph range) with the rapid approach of the next system. Temperatures will rise a couple degrees today to the mid 20’s F at the ridgetops and low 30’s at sea level.

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).

Graham will issue the next advisory Thursday morning December 27th.

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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