Wed, March 09, 2016 Turnagain Pass Avalanche Forecast

Wed, March 9th, 2016

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

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

This has been an active week so far with glide avalanches releasing in popular terrain on the motorized and non-motorized sides of the highway. Yesterday we received a report that the Cornbicuit glide crack released recently; it is worth checking out the observation. This type of avalanche would be unsurvivable. Luckily they are avoidable. Steer clear of existing glide cracks.

Looking down the path of the Cornbiscuit glide avalanche. Photo: Chad Saetre

Close up of the Seattle Ridge glide avalanche crown. There is still more glide crack that could release.

Avalanche Problem 2

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

It is still possible to find a shallow pocket of wind slab in steep leeward terrain. These will be most hazardous if you happen to trigger one in a high consequence spot that takes you for a ride over a cliff or into a terrain trap. Look for old stiff pillowed snow and cracking or hollow sounds while traveling.

Loose snow: Loose snow sluffing will warrant management today if skiing the steeps. Sluffs have been reported to be fast moving with the ability to entrain a significant amount of surface snow in big terrain. This will be more pronounced on cooler, shadier North aspects.

If the sun shines on southerly slopes it may be possible to get some surface snow moving as it warms and have wet loose snow activity.

The Seattle Ridge Weather Station is back online after a de-riming mission. Check out the weather link for any recent wind loading HERE.

Additional Concern

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

Avoid travel on or underneath the large cornices that loom over much of the leeward Alpine terrain. We continue to receive reports of these releasing naturally and you definitely do not want to trigger one on your snowmachine or skis. They often break much farther back than you expect and additionally there may be a deep cornice crack along the ridgeline to fall into.

Weather

Wed, March 9th, 2016

Yesterday was described as a little bit of everything from completely obscured to patches of blue sky and sun. Temperatures were in the mid 20Fs and easterly winds were light.

Today is forecasted to be partly to mostly cloudy with temperatures in the mid 20Fs to mid 30Fs and light easterly winds. Tonight and tomorrow will be similar with minor cooling overnight.

As we move into the weekend there is a chance of snow as the low in the Gulf spins some moisture into the advisory area but overall the weather looks to be fairly benign.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	34	0	0	135
Summit Lake (1400′)	33	0	0	43
Alyeska Mid (1700′)	32	trace	trace	107

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	23	ENE	10	31
Seattle Ridge (2400′)	25	ESE*	11*	31*

*Seattle Ridge winds were back online at 11 am yesterday.

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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