Thu, February 13, 2014 Turnagain Pass Avalanche Forecast

Thu, February 13th, 2014

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

1 - Low

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

Persistent Slabs

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

More info at Avalanche.org

By far the most common problem is related to recent snow on top of the prominent crust layer. The 16+ inches that Turnagain Pass received on February 7th have been responsible for many reported avalanches since that storm. The general trend of these avalanches is – small in size (12-20″ deep), lower volume, decent propagation across wind stiffened steep slopes. Check out the observations page for a bunch of photos from the last 6 days, and this observation for a good quick synopsis of the problem.

The 2 properties necessary to create avalanches that are not always found –

1. A cohesive slab – some wind loading and stiffening is necessary to create connectivity of the surface snow, otherwise it’s just loose powder with sluff potential.

2. A faceted interface between the new snow (Feb 7th storm) and the underlying crust (January melt/freeze) or old snow. In places where the facets are present, this is a significant weak layer consisting of large loose grains with poor bonding.

Weather

Thu, February 13th, 2014

Cold high pressure from early in the week has transitioned to a showery precipitation pattern as of yesterday afternoon. A few inches of fresh light powder have fallen since Wednesday. Temperatures remain quite cold, especially for snow to be falling, reaching into the negatives at many of our local weather stations. Wind is generally light, although since about 4am the wind has increased slightly and switched over to a East Northeast direction. Expect cloudy skies today with snow showers and 2-4 inches of snow accumulation today.

The extended forecast looks like more of this same pattern. A low pressure system is anchored over the northwestern gulf, and expected to stay there well into next week. Most precipitation from this event will be showery, but there is a chance for heavier snow events by the weekend.

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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