Fri, February 14, 2014 Turnagain Pass Avalanche Forecast

Fri, February 14th, 2014

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

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 continue to document loose and very weak facets between the January melt/freeze crust and the February 7th storm snow. This layer was responsible for a number of small human triggered avalanches in the last week. It continues to be the most likely culprit for significant avalanche activity today, especially when combined with new snow and wind. Check out this observation for photos and snowpit data regarding the facet layer.

Avalanches witnessed on this layer have thus far maintained a consistent pattern with relatively small size (12-20″ deep), and lower volume. Keep in mind that bigger and steeper terrain will produce larger and more dangerous avalanches. With more snow and wind the depth of this slab layer will be reaching 24-30″ in wind loaded areas.

The 2 properties necessary to create this type of avalanche that are not always found –

1. A cohesive slab – some wind loading and stiffening is necessary to create connectivity of the surface snow, otherwise it’s just loose powder with sluff potential.

2. A faceted interface between the new snow (Feb 7th storm) and the underlying crust (January melt/freeze). In places where the facets are present, this is a significant weak layer consisting of loose sugary grains with poor bonding.

Avalanche Problem 2

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

Yesterday afternoon we witnessed a very small natural avalanche occur during a short spell of wind. Our light dry snow on the ground is easily transported by wind and wind slab can build quickly with only moderate wind velocities. Additional storm snow by itself is probably not enough to be a significant avalanche problem, but combined with wind it will produce pockets of unstable snow.

Wind slab is expected to be isolated to higher elevations above treeline, and may not form if the wind stays light today.

Weather

Fri, February 14th, 2014

Just a couple inches of snow had fallen yesterday before we got a clear break and periodic wind activity. Wind was reaching gusts to 52 mph and blowing snow around at ridgetop levels.

The large low pressure system over Kodiak is sending our region waves of cold precipitation today. As of this morning we have another 3-5 inches of snow on the ground and it is forecasted to continue through the end of Friday. Wind has backed off a little. Temperatures remain cold but are increasing slightly. Currently Center Ridge snotel is reading 11.5 degrees.

Unsettled storm patterns will continue through the weekend, originating from the low pressure system in the northwest gulf. We can expect more of the same weather for a few more days.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
05/13/24	Turnagain	Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South	H Thamm
05/13/24	Turnagain	Observation: Turnagain Pass non-motorized side	Amy Holman
05/12/24	Turnagain	Observation: Warm up Bowl	Tony Naciuk
05/07/24	Turnagain	Observation: Turnagain Pass Wet Slabs	A S

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