Wed, April 13, 2016 Turnagain Pass Avalanche Forecast

Wed, April 13th, 2016

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

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

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

New glide activity was observed yesterday and continues to be the primary concern due the destructive and unpredictable nature of the releases. Travel underneath existing glide cracks is a total gamble. The zone above and around the popular motorized up-track on Seattle Ridge continues to have our hackles up. This well traveled slope is hanging in the balance (pictured below). Although much of the snowpack has already avalanched along Seattle Ridge, there is still a lot of snow that could release. There was no overnight freeze in the 1000-2500′ elevation band and there is the possibility of rain today. These weather factors may increase glide activity.

Due to the dangerous and destructive power of even a small glide avalanche, we are recommending that people do not travel in avalanche terrain (including runout zones) on the motorized side of Turnagain Pass (West Side). Glide avalanche hazard also exists on the non-motorized slide of Turnagain Pass. Travel underneath existing glide cracks is not recommended. In addition, be on the lookout for new glide cracks forming.

An example of new glide avalanche activity (from the past 24-hours). photo: Tim Glasset

Looking towards the uptrack and noting the amount of snow that still could slide.

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

Yesterday the temperatures rose above freezing in the Alpine and the sun was shining. The new snow got progressively wetter throughout the day. There was some minor natural roller ball activity and some natural wet loose activity on steep slopes. Low elevations were very punchy and saturated in the afternoon. There was no overnight freeze from 1000′- 2500′. This combined with the possibility of rain will up the likelihood and potential for natural and human triggered wet loose avalanches today. Any periods of sunshine will also be a factor. Remember wet loose avalanches can be hard to escape once initiated and particularly hazardous if they push you into a terrain trap.

Natural wet loose avalanche on Seattle Ridge that occurred in the afternoon yesterday.

Additional Concern

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

Yesterday it was evident that the wind had redistributed the new snow and there were deeper pockets of snow along leeward ridgelines. We have limited information from the Alpine but traveling to 3200′ showed a structure that could be triggered on steep wind loaded slopes. Wind effected storm snow sits on top of a stout melt-freeze crust. Watch for cracking while traveling and recognize that this set-up could be sensitive on unsupported features.

Cornices: We have been wondering when we will see a natural cornice fall cycle. So far they been “hanging in there” but yesterday we observed two cornice falls and the avalanches that were triggered by them in Portage Valley. These were both in terrain at or below 2500′. This is similar to the corniced ridgeline elevations in the Seattle Creek drainage. Continued warm temperatures may increase the likelihood that these will fail. As always, avoid travel on or under cornices at any elevation and remember that they may break farther back than expected.

Weather

Wed, April 13th, 2016

Yesterday was mostly sunny with some high clouds. Sky cover trended to overcast by the evening. Winds were light and variable. Temperatures were warm, averaging in the high 40Fs at 1000′ and the high 30Fs at 3000′. Center Ridge Snotel hit 50F at 4 pm and Sunburst Wx station saw 34F at 3 pm.

Today will be partly to mostly cloudy with a chance of rain in the afternoon. The temperatures will remain warm and above freezing above 3000′. Wind will be light and easterly.

The trend for the week is forecasted to be scattered showers and above average temperatures as the general pattern stays the same.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	41	0	0	114
Summit Lake (1400′)	40	0	0	31
Alyeska Mid (1700′)	38	0	0	99

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	32	variable	5	33
Seattle Ridge (2400′)	34	variable	3	18

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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