Thu, April 04, 2013 Turnagain Pass Avalanche Forecast

Thu, April 4th, 2013

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

2 - Moderate

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

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

Wet avalanches will again be our primary concern today likely becoming active on southerly slopes late in the day as the snowpack continues to absorb solar radiation, subsequently weakening the bonds between individual grains. This is the “melt” process of the melt-freeze cycle. Pay attention to the snow surface throughout the day. Indicators of the avalanche danger rising will come in the form of point releases, roller balls on steep slopes and a boot penetration above your knees. If you are seeing any of these signs it’ll be a good idea to avoid steep slopes on the south end of the compass, as these are all indicators of our snowpack losing strength.

As seen in this photo below, sun induced slabs are also of concern this week. These have been relegated to the upper most layer of our snowpack with no signs of stepping down into older snow, though a potential for wide propagation exists.

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

Today will be the 5^th day in a row of a melt-freeze cycle with cornices undergoing the same diurnal changes as the snowpack. Once the day heats up and individual snow bonds weaken, cornices will be more likely to fail spontaneously. As was the case on Goat Mountain (Girdwood Valley) Tuesday, cornice failure may trigger a slab avalanche once it fails, neither of which you want to be involved with today. Continue to use good judgment around cornices and avoid prolonged exposure, specifically late in the day.

ADDITIONAL CONCERNS

There is still some uncertainty on northerly slopes where shallow wind slabs have been found to be reactive on buried surface hoar and near surface facets. The good news is that our mid-pack is showing respectable signs of strength and wind slabs from last weeks storm don’t appear to be stepping down into deeper layers.

Weather

Thu, April 4th, 2013

Yesterday was another beautiful spring day in the backcountry. SE winds in the teens and low 20’s kept the snow surface cool enough that we didn’t experience much avalanche activity.

Today looks to be another warm day on tap with temperatures reaching mid-40’s at 1000 feet and winds very light out of the east. Direct sun and less wind than yesterday will contribute to a rise in the avalanche danger this afternoon. No precipitation is expected to fall today.

Temps will again fall overnight though they may not rebound quite as high as we’ve seen this week as a colder air mass begins to move into our area from northwestern Canada.

Kevin will issue the next advisory on Friday, April 5th.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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