Fri, March 04, 2016 Turnagain Pass Avalanche Forecast

Fri, March 4th, 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

Glide avalanches continue to release and glide cracks are growing daily. An observer on Wednesday noted movement in the Cornbiscuit glide crack over the course of two ski runs. There was glide avalanche that was observed on south face of Manitoba yesterday that occured sometime between 12 pm-4pm. Glide avalanches are still totally unpredictable and travel underneath glide cracks should be avoided.

Recent glide avalanche in the Seattle Creek drainage. This was initially observed Wednesday afternoon and Wendy got a photo of it yesterday.

The Cornbiscuit glide crack is huge, growing and scary… It is worth checking out the other photos from the observation on Wednesday.

Photo: Kevan Dee

Avalanche Problem 2

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

The cornices are impressive and hang over many slopes in the advisory area. There was a report of a snowmachine triggered cornice fall in Warmup Bowl on Wednesday that took the rider by surprise. They luckily did not go over with the falling chunks of snow. Cornices have the potential to be quite dangerous if you take ride with them or if they fall from above onto you. Avoid travel on top, watch for cornice cracks and limit exposure while traveling below. We are not ruling out the possibility of a large cornice fall triggering an avalanche on the slope below due the massive loading potential.

Snowmachine triggered cornice fall in Warmup Bowl on Wednesday.

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

Today is a transitional day as we say goodbye to the sunshine and the clouds move in with the possibility of snow showers. Depending on the thickness of the cloud cover we may still see some surface warming of the snowpack. We have had no reports of human triggered avalanches in the past few days. There is still the possibility of triggering lingering wind slabs in steep leeward terrain, especially unsupported convex slopes. If you are out in the mountains it is worth checking out surface conditions, as these will be what the next wave of snow hopefully bonds to. Southerly slopes have a crust; there have been reports of small surface hoar formation in some areas and in protected areas loose snow is starting to facet. In addition there is a wide array of wind-affected snow at higher elevations and a delightful rain crust lower down.

Loose snow avalanches: Steep protected areas have loose snow that may be enough to push you off your feet if it gains enough force and mass as it travels down slope with you. Manage your sluff by moving out of its path before it hits you.

Surface conditions at Turnagain pass.

Weather

Fri, March 4th, 2016

Yesterday was clear and sunny. There were some patches of valley fog. Temperatures were in the mid 20Fs to upper 30Fs. The winds were light and easterly. Temperatures dropped into the high teens to mid 20Fs overnight.

Today will be mostly cloudy with a chance of snow in the morning, increasing in the afternoon. 0-3″ of snow is possible. East winds will be light and temperatures will be in the mid 20Fs to 30Fs.

Rain and snow showers are forecasted tonight and tomorrow. This pattern will continue through the weekend as a low in the Gulf spins a series of weather systems into the area.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	26	0	0	138
Summit Lake (1400′)	23	0	0	42
Alyeska Mid (1700′)	25	0	0	104

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	22	ENE	10	22
Seattle Ridge (2400′)	25	–	–	–

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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