Mon, January 20, 2014 Turnagain Pass Avalanche Forecast

Mon, January 20th, 2014

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

3 - Considerable

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

Winds over the last day have blown enough to transport snow and create new slabs 2-3’ in depth in the higher elevations. Winds today out of the East will continue to build slab depths on leeward slopes. We currently have very limited information from the upper elevations. If venturing into the higher elevations today, treat wind loaded areas with a healthy dose of suspicion. Wind slabs that have formed over the past day and continue to build today have the potential to slide easily. This problem on its own is enough to bury a person. Add into the mix the chance of triggering a deep slab and the end result could be grim.

It is important to know how to recognize snow that has been wind loaded. Smooth, rounded and pillowy are a few ways to describe the look of wind slabs. Snow will feel more stiff in wind loaded areas. Shooting cracks are an obvious sign of a wind slab that is unstable.

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

This past weekend brought much needed precipitation to the area. Rain fell up to 2,500’ but changed over to snow by Friday afternoon. The upper elevation starting zones have received well over 2’ of snow in the past 3 days. At the bottom of the snowpack, up to 5’ down in some locations, is weak snow. In many places it will be difficult to impact that weak snow that is far below you. However, snow does not sit uniformly across the mountains. Snow depths will vary from 1-5 feet in the upper elevations. It is in these spots with thin snow coverage that need to be avoided. The likelihood of triggering a deep, unsurvivable slab will go up if people hit thin spots. The obvious signs of unstable snow will not necessarily be present. Snowpit tests may or may not always point to this problem. In order to understand this problem it is crucial to know the history of the season up to this point. History tells us that the foundation is weak and not trustworthy.

This video shows the problem. It takes a lot of force to trigger a slab in this test. Once it does fail the entire snowpack (column in this case) slides.

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 temperatures and rain have done a number on the snowpack at the lower elevations. Warm temperatures in the lower elevations will persist throughout the day. While the chances of wet slabs releasing have gone down over time, the threat of dangerous wet loose avalanches is something to be aware of. Avoid steep terrain in the lower elevations today. If your snowmachine, skis or board is punching through the entire snowpack, it is definitely time to back off of steep terrain. Pay attention to what is below as well. Terrain traps such as trees, cliffbands and gullies will amplify the consequences of being caught in a wet loose avalanche today.

Weather

Mon, January 20th, 2014

In the past 24 hrs the mountains around Eastern Turnagain Arm have received 6 € of new snow with .6 € of water equivalent. Ridge top winds have been out of the East averaging 36 mph with gust to 86 mph. Temperatures have continued to remain mild, with freezing level up to 2,000′ overnight. The Sunburst station at 3,812′ has averaged 22 deg F.

Today expect light snow/rain and mild temperatures. Winds will be out of the East at 40 to 50 mph. Snowfall in the upper elevations will accumulate up to 3 € with rain/snow line around 1,300 feet above sea level. Temperatures at 1,000′ will be in the high 30s F.

We will remain under the influence of an active weather pattern and a general Southerly flow over the next several days. Expect temperatures to remain mild and precipitation to be on and off through the 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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