Fri, December 18, 2015 Turnagain Pass Avalanche Forecast

Fri, December 18th, 2015

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

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. 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

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

Dec.17 Storm Totals:
Turnagain Pass Center Ridge: 13”
Girdwood Midway: 5”
Summit Lake: 3”

Yesterday warming temperatures and sustained Northeast winds have left 1-2’ of upside down storm snow in Turnagain Pass. This snow proved tender yesterday and shooting cracks were observed above 2000’ in places where the snow felt stiffened by the wind. No avalanche activity was reported, but visibility was poor making it difficult to see if any natural avalanche activity occurred.

Today weather conditions will deteriorate again with the arrival of yet another storm that is expected to intensify this evening. Easterly winds will start building this morning along with snow showers by early afternoon. This weather will be adding stress to an already stressed out snowpack. Triggering a slab 2+’ deep will be more likely on unsupported terrain features like steep convex rolls, gullies, and above cliffs. Poor visibility is expected today, but should you choose to travel into the upper elevations, maintain a conservative Jedi mindset. Use stability tests like hand pits or ski pole tests to feel for upside down snow; denser snow sitting on weaker snow. Most of all don’t be tempted by the Dark Side (large open slopes.) Patience you must have!

Shooting cracks observed yesterday on Tincan and a 15″ slab failed easily above the skin track where snow was unsupported.

Avalanche Problem 2

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

We have been tracking several layers of weak snow formed in early December that are now buried under 3-4’ of snow. Poor visibility and dangerous avalanche conditions have made it difficult to evaluate this problem in the upper elevations where a large trigger, like a snowmachine, could find a sweet spot. This is one of the those low likelihood/high consequence problems that is unlikely to occur naturally and is not manageable. This is one more reason to avoid large steep slopes until the snowpack can adjust to its new load.

Weather

Fri, December 18th, 2015

Yesterday a total of 13 € of new snow was recorded at the Turnagain Pass Center Ridge weather station. Sustained moderate winds from the Northeast became light yesterday, but not until most of the snow had already fallen. Temperatures warmed to above freezing, and rain/snow line reached 1200′ by mid afternoon.

Overnight no new precipitation was recorded, winds remained light, and temperatures cooled just below freezing (32F) at sea level.

Today Easterly winds are expected to start building this morning with the arrival of more snow. Snow showers will intensify by this evening and could bring another 1′ of new snow by tomorrow. Temperatures will be hovering around 32F making it possible for rain at sea level.

*Weather station data is taken from 6am yesterday to 6am today. Yesterday’s storm totals were calculated with the addition of yesterday wx station snow totals.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	30F	4	0.4	49
Summit Lake (1400′)	28F	1	0.1	17
Alyeska Mid (1700′)	31.5F	0	0.03	34

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	24F	NE	11	36
Seattle Ridge (2400′)	27F	n/a	n/a	n/a

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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