Tue, January 21, 2014 Turnagain Pass Avalanche Forecast

Tue, January 21st, 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

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

It is another wet and windy storm day in the Girdwood and Turnagain Pass area. Light rain fell yesterday up to 2000’ and has intensified overnight. Rain will persist through the day today adding up to another .75” of water. That said, wet avalanches due to continued rain on snow will be the main concern below treeline.

We have seen very little natural avalanche activity since Friday’s heavy rain event and widespread avalanche cycle. However, there was one wet slab noted on the Southeast face of Seattle Ridge just below treeline (photo below). This avalanche is one of the smaller wet slabs we have seen lately but it does show that the pack is still adjusting to the rain on snow – this can also be seen in Fitz’s video HERE from Sunday. With today’s increase in precipitation we could see a few more natural wet slabs release.

Natural wet slab avalache likely occurring Sunday or very early Monday. (1800′, SE facing, 12-18″ deep x ~150′ wide)

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

Above treeline our snowpack is getting deeper by the day. We have had up to 3’ of dense heavy snow fall since Thursday night. Yes, this is good news for the upper elevations in the long term, but for the moment it is creating a dangerous deep slab avalanche problem. The weak faceted snow near the base of the snowpack was overloaded by Friday’s rapid loading event and several large full-depth avalanches occurred. Some of these propagated across entire slopes and deposited deep debris piles. This natural activity has since settled down and stability tests show likelihood of triggering becoming harder and harder but if it does go a deep and destructive avalanche is likely. With the continued stormy weather, warm temperatures, and very little upper elevation information, the deep slab issue continues to deserve much respect.

In short – this is a highly unpredictable but highly consequential avalanche problem.

Additional Concern

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

In the upper elevations (above 2,500’) where it has been and will continue to snow, storm snow instabilities will be a concern. These are mainly in the form of wind slabs near the upper elevation ridgelines. The Easterly winds have been strong for over 24-hours on the ridgetops. Though wind slabs were abundant yesterday around 3,000’ they were shallow (6-8″ thick), stubborn and hard to crack. However, the higher one goes in elevation the more sensitive, and larger, they should be.

Cornice growth
Cornices have been growing substantially the past several days. A cornice fall right now has the potential to trigger a large deep slab avalanche. This is one more reason to steer clear of runout zones.

Weather

Tue, January 21st, 2014

Another pulse of warm, wet and windy weather is over us currently. During the past 24-hours we have seen .7 € of rain at the Turnagain Pass SNOTEL (1880′). Another .75 of rain is expected today. Temperatures have been in the upper 20’sF on the ridgetops and low 40’sF at sea level. Wind has been strong with averages around 50mph and gusts to 96mph from the East.

Temperatures today are expected to be in the mid to upper 20’s on the ridgetops and low 40’s at sea level. The rain/snow line will be around 2000′ once again with .75 € of rain expected below this and up to 8 € of heavy snow up high. Winds will remain out of the East with averages in the 60-70mph range.

The next several days look to remain warm and stormy. Models are hinting at a possible clearing by the weekend.

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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