Fri, January 29, 2016 Turnagain Pass Avalanche Forecast

Fri, January 29th, 2016

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

1 - Low

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

Approximately 3′ of snow or 3″ of rain has fallen in the advisory area since the storm started Tuesday night. This combined with strong ENE winds Tuesday through Thursday has created dangerous conditions in the mountains. Visibility was limited yesterday but fresh debris from a large natural avalanche was observed off of Seattle Ridge. The snowpack will still need time to adjust to this load today and allow the new snow to bond to the old snow surfaces. Elevated caution is advised. Slab depth, especially in wind loaded areas could be deep and very dangerous. Avoid slopes steeper than 30 degrees and be aware of what terrain is above you. Triggering a wind slab in leeward areas is likely. Look for patterns of wind loading, steer clear of stiff pillowed snow and watch for shooting cracks.

The warm wet snow combined with wind is prime cornice building conditions. Avoid travel underneath or on top of these today. They may easily fail naturally or under the weight of person or machine. When they fall they could overload slopes below and trigger a large avalanche.

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

A majority of the precipitation that fell on the snowpack in the Treeline elevation band (1000′-2500′) has been in the form of rain or very wet snow. This has created saturated conditions and the potential for wet loose and wet slab avalanches. This may change throughout the day as the temperatures are forecasted to drop. This could help stability increase as the snowpack freezes. On the flip side watch out for areas that receive direct sunshine (south facing) if skies clear, this may increase wet loose activity. We are at that point in the AK winter season where this will start becoming an issue. Avoid travel on steep slopes in this elevation band, especially areas where you could end up in a terrain trap.

Wet debris from Seattle Ridge. This avalanche ran almost into the flats near the motorized lot on Turnagain Pass yesterday.

Additional Concern

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

Limited visibility yesterday made it hard to see how the glide cracks were behaving. The snowpack received extra weight and lubrication from rain and warm temperatures. This may cause increased glide activity and so may the cooling temperatures throughout the day. Glides are totally unpredictable. Avoid travel underneath them. We sound like a broken record as they have been in the forecast now for weeks however; they are really not something to mess with.

Weather

Fri, January 29th, 2016

Yesterday skies were mostly cloudy with some clearing in the afternoon. Rain and snow continued to fall adding an additional .5″ of precipitation (5+” of snow above 1500′) to the snowpack. This brings our storm total to right around 3” of H2O (2-3′ of snow). ENE winds decreased throughout the day becoming calm overnight and temperatures were in the mid 20Fs @ 3000′ and in the mid 30Fs @ 1000′.

Today there will be scattered rain and snow showers mostly before noon with a clearing and cooling trend throughout the day. Winds will be calm and temperatures will be in the mid 20Fs to mid 30Fs. Tonight temperatures are forecasted to drop down into the teens and there is a chance for isolated snow showers.

Saturday will be mostly sunny as a stabilizing ridge dominates the weather pattern for the day. Clouds move back into the area overnight. Stay tuned for the next round of stormy conditions next week.

PRECIPITATION 24-hour data (6am – 6am)

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	30	0	.3	97
Summit Lake (1400′)	34	0	.1	28
Alyeska Mid (1700′)	33	4.5	.7	72

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	26	E*	10*	41*
Seattle Ridge (2400′)	27	n/a	n/a	n/a

*Sunburst anemometer has been down since 7 pm, 1/28.

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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