Thu, March 03, 2016 Turnagain Pass Avalanche Forecast

Thu, March 3rd, 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

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

Cornice fall may be one of the larger hazards today with sunshine acting to weaken these already tenuous bombs. Cornices right now are LARGE and UNPREDICTABLE– some bigger than semi-trucks and some with large cracks extending their full length. Yesterday melting snow and dripping water could be seen on cornice faces during the heat of the day along Magnum Ridge. Today the sun will continue to weaken cornices making human triggered (snowmachine or skier) and natural cornice fall more likely in the afternoon. Limiting time spent under these is key and giving them extra room along ridgelines will be necessary. Not only would it suck to trigger a cornice while on top of one, imagine what it would be like if people were also below it. Evaluate all ridgelines and slopes for potential cornice fall and be weary of existing skin tracks and up-routes. There are many areas where the “normal” route is in the line of fire.

Magnum Ridge Cornice – The estabilshed skin track is directly on top of 30-40′ cornice feature.

Same corniced ridge on Magnum. Note the long crack observed on February 18th before a 10 day storm added more weight and stress to this cornice. Photo by Amanda Goss.

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

Strong winds during a 10-day storm have created layers of wind-affected snow throughout Turnagain Pass. Observations over the last several days have been showing this problem to be stabilizing, however today’s warm temperatures and direct sun could be a catalyst for a human triggered wind slab. Triggering a wind slab is still possible on slopes steeper than 35 degrees especially on slopes with unsupported terrain features. Ease into steeper terrain with caution and avoid solar aspects if you find moist surface snow or see wet loose point releases in motion.

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

Glide cracks are moving and coming out of hiding after they were covered by wind and snow during the storm cycle. Although it has been several days since the last glide crack we know of released and avalanched, they are still on the move. Limiting time spent under cracks is crucial, as they will mow anything down in their path if one does release.

Very large glide crack on the SW shoulder of Cornbiscuit – view from the Seward Hwy. The entire SW face of Cornbiscuit has extensive glide cracks. Click HERE for more pictures from yesterday.

Weather

Thu, March 3rd, 2016

Yesterday skies were clear and sunny and temperatures reached mid-high 30’s F during the warmest part of the day, around 2pm. Calm winds switched directions mid day from an Easterly direction to a Westerly direction. Overnight skies remained clear and temperatures dropped into the teens to mid 20’s F.

Today Westerly winds are expected in increase slightly 10-15mph along ridgetops. Skies will remain sunny and day time temperatures are expected to spike mid day.

Tomorrow a pattern shift is expected with a possibility of scattered snow showers.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	27	0	0	140
Summit Lake (1400′)	22	0	0	42
Alyeska Mid (1700′)	28	0	0	105

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	28	NE becoming W	4	10
Seattle Ridge (2400′)	24	n/a	n/a	n/a

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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