Sat, February 28, 2015 Turnagain Pass Avalanche Forecast

Sat, February 28th, 2015

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

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. Dangerous avalanche conditions.	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

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 long dry spell back in late January created a layer of weak faceted snow that has now been buried by several storms. These storms produced several slabs that now average 2 feet in thickness in the Alpine. The combination of slab over weak layer can be found consistently above 2,500’. The two areas that are most unstable are:

Steep terrain between 2,500-3,000’. The slab/weak layer combo is sitting on a firm crust in this elevation band. The slab is thinner in this lower half of the Alpine, making it easier to impact the weak layer. Parties continue to report collapsing in this elevation band and test results point to continued unstable snow in this zone.

Steep terrain with a Southerly component. A stout sun crust formed over 10 days ago in this terrain and has slabs in the 1 foot range sitting on it. We have seen sporadic natural activity in this type of terrain recently and mainly on the periphery of the forecast area.

While it has been 7 days since the last loading event, the nature of a persistent weak layer is that is can remain active for a long time. If you’re considering getting into committing terrain keep in mind that you may find the most unstable snow well below starting zones. Because of this it will be important to pick lower angle terrain (35 degrees or less) and slopes that provide escape options along the way.

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

A few inches of new snow will fall by the evening hours in the higher elevations. Very shallow slabs in the 6” range will form and be sensitive to human triggers in steep (40 degrees and over) terrain. This is not a significant hazard but is worth keeping in mind if you are travelling above terrain traps such as cliffs, gullies, or trees.

Weather

Sat, February 28th, 2015

The past 24 hours brought mild temperatures and increasing cloudiness to the area. Winds were light out of the East and no new precipitation fell.

Today expect cloudy skies with light snow in the afternoon. Snow accumulation will be light, in the 1-2 € range. Temperatures will be mild with ridgetops climbing into the high 20s F and a rain/snow line around 1,000′. Ridgetop winds will be out of the East at 5-10 mph.

The thin band of moisture that will deliver a quick shot of snow will be replaced by high pressure by Sunday morning. A large low pressure system will move across the Bering Sea and connect with a low in the North Pacific in the early part of next week, bringing the next chance for precipitation on Tues night.

PRECIPITATION 24-hour data (6am – 6am)

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	33	0	0	40
Summit Lake (1400′)	29	0	0	6
Alyeska Mid (1700′)	27	0	0	23

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	30	E	7	26
Seattle Ridge (2400′)	31	NW	13	28

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
11/16/23	Turnagain	Observation: Tincan Common	William Finley
11/14/23	Turnagain	Observation: Sunburst/Magnum	Adrian Beebee
11/14/23	Turnagain	Observation: Seattle Ridge	Schauer/ Creighton/ Ellis Forecaster
11/13/23	Turnagain	Avalanche: Tincan Trees	Eeva Latosuo
11/12/23	Turnagain	Observation: Sunburst	Schauer/ Creighton/ Nave Forecaster
11/12/23	Turnagain	Avalanche: Goldpan – avalanche	Mike Records
11/11/23	Turnagain	Observation: Tincan Common	Andy Moderow
11/11/23	Turnagain	Observation: Taylor Pass – Sunburst	Wadsworth / Stwertka
11/10/23	Turnagain	Observation: Tincan	Andrew Schauer Forecaster
11/10/23	Turnagain	Observation: Tincan Trees	Michael Kerst

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