Fri, March 14, 2014 Turnagain Pass Avalanche Forecast

Fri, March 14th, 2014

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

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

Rapid loading has been occurring overnight. New snow amounts over the past 24 hours are in the 12-18” range on Turnagain Pass. This newest load has come on the heels of over 3 feet of new snow from earlier in the week. An additional 10″ of snow today will only add to the problem. This all boils down to a simple rule of thumb: snow does not like rapid change.

Included in Storm Snow concerns are Wind Slabs. Starting zones, cross loaded gullies and leeward slopes hold the potential for harboring sensitive wind slabs. Dense thick slabs up to 5 feet in depth have the potential to release naturally today. These slabs will be most sensitive as they are forming. Be on the lookout for rounded and smooth snow surfaces. Shooting cracks will be the first indicator that you are on a wind slab.

Failure within the storm snow layers could be anywhere from 1-5′ deep today. Avalanches occuring in these upper layers have the potential to step down to deeper layers in the snowpack.

Avoidance of avalanche terrain is essential today. This includes staying off of slopes 35 degrees and steeper, avoiding wind loaded areas and being far away from runout zones. It is critical to know what terrain is above you, especially when visibility is poor.

Avalanche Problem 2

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

While the arrival of Winter Part III is welcome from a recreational perspective, it has also created a Deep Slab problem. Prior to March 10th the snow surface was comprised of a well developed layer of weak snow sitting on a crust. This combination was observed throughout the forecast area. That interface is now buried by as much as 5’ and on average over 3’ of snow. While it might be difficult to immediately affect this interface due to its depth, it is still the layer that is most concerning. (see video HERE for an explanation of this issue)

Avalanches failing at this interface have the potential to be high volume and unsurvivable. The travel advice related to this problem is the same-avoid being on or in the runout of avalanche terrain.

Additional Concern

Wet Loose

Wet Loose

Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

More info at Avalanche.org

Warm temps and rain at sea level will allow for the chance of encountering wet loose avalanches in steep terrain. The observed rain snow line was around 500’ in elevation last night. If you find yourself slogging in wet snow below 1,000’ it will be important to stay off of any terrain over 35 degrees.

Weather

Fri, March 14th, 2014

The snow continues to pile up! In the past 24 hours the Center Ridge SNOTEL site on Turnagain Pass has picked up 18 € of snow with 1.6 € of water with similar amounts in the Girdwood Valley. Ridgetop winds (Sunburst station) have averaged 52 mph out of the East with a max gust of 97 mph. Temps on ridge tops have remained in the low to mid 20s F. The rain/snow line has hovered around 500-800′.

Today expect a continuation of snow and wind. Another 6-10 € of snow with .65 € of water is possible today. Temperatures at 1,000′ will be around 32 F. Winds will back off slightly but still average in the 35-45 mph range.

Snowfall should taper off tonight. Temperatures (at 1,000′) will also drop into the teens by the nighttime hours. The extended outlook shows more of the same (snow & wind) heading into the weekend and early part of next week.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
04/29/24	Turnagain	Avalanche: Turnagain aerial obs	Tully Hamer
04/27/24	Turnagain	Observation: Johnson Pass	Noah Mery
04/23/24	Turnagain	Observation: Turnagain Sunny Side	Travis SMITH
04/21/24	Turnagain	Observation: Bertha Creek	Anonymous
04/20/24	Turnagain	Avalanche: Spokane Creek	Schauer/ Mailly Forecaster
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster

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