Sun, January 19, 2014 Turnagain Pass Avalanche Forecast

Sun, January 19th, 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

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 storm pushed us into a deep slab problem at higher elevations. This means that we now have average slab depths of greater than 1 meter sitting on top of a persistent weak layer. The avalanche implications are the same as we’ve been seeing, but the volume and destructive force have increased.

With deep slab concerns a backcountry traveler will probably not see obvious signs of instabilty (whumphing, shooting cracks) until the slab actually avalanches. It is unlikely to be triggered at the deep points, but rather at the thinner edges near scoured ridges or exposed rocks. It may propagate large distances where it then pulls the deeper pockets. It may allow multiple tracks before somebody finds the trigger point and avalanches the entire slope.

Deep slab is a low probability, high consequence problem. With continued precipitation, warm temperatures, and high wind – steep terrain should be avoided. When active weather abates the safe terrain options will get better with time.

This photo is on Moose mountain, above Canyon creek.

Avalanche Problem 2

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

Below 2000 feet we had significant rain on snow on Friday. We can expect more rain today, perhaps as high as 1200 feet. The photos below show an example of the abnormal avalanche activity that can happen with rain and warm temperatures. This is fairly low in the Tincan trees. 3 distinct pockets released sympathetically on the steeper rolls as the weak layer collapsed. Debris from this was very dense.

Tincan avalanche 1550 ft elevation. 200 feet high by 1000 feet wide. 2-3 feet deep.

Weather

Sun, January 19th, 2014

Friday’s storm deposited over 2 feet of snow at high elevations and over 3 inches of rain or snow water equivalent at some low elevations. Saturday gave us a break in the storm, but temperatures did not drop significantly.

Today, more rain and snow is expected. Another pulse of moisture is approaching from the south, originating at a deep 956mb low pressure center. Up to another inch of water is forecasted for the next 24 hours, with the bulk of that precipitation happening tonight. Temperatures will increase throughout the day, and snow level will rise from 500 feet to 1200 feet. Look for a southeast wind 51-74 mph, also increasing slightly as the day progresses.

Expect continued warm temperatures through the week with more rain and snow possible.

Current satellite image.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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