Fri, December 19, 2014 Turnagain Pass Avalanche Forecast

Fri, December 19th, 2014

Alpine

Above 2,500'

3 - Considerable

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

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

Our main avalanche concern today is one that will not go away quickly. Surface hoar that formed a week ago has been preserved and is sitting below 1-3’ slabs. Typically surface hoar gets knocked over and blown around before a slab builds on top of it. That is not the case with our current snowpack. The snowfall that began on December 13th came in with very little wind and allowed this layer to be buried intact. We have been investigating this layer over the last several days and we have found it in all pits above 2,700’.

The tricky part with this set up now is that it is gradually becoming more difficult to trigger an avalanche. We know this based on our test results in snow pits. Unfortunately, it will be possible to test this layer by traveling in steeper terrain and not get results (NOT RECOMMENDED!) Exceptions to this were found on Sunburst and in the Summit Lake region, where skiers remotely triggered an avalanche from 50’ away. In areas such as this where the snowpack is thinner, it will be easier to initiate an avalanche today.

The nature of buried surface hoar is such that it persists as a weak layer in the snowpack for many days, sometimes weeks after it becomes buried. Because of this we will be tip toeing around the mountains for the foreseeable future.

In order to stay out of trouble it is best to avoid steep terrain. Terrain on all aspects over 35 degrees should be treated as suspect. Avalanches, if initiated have the very real potential of propagating across large areas, making escape difficult at best. There is plenty of evidence to support this and the problem will potentially take a long time to go away.

Below 2,500’ in elevation the likelihood of triggering a slab avalanche 1-2’ in depth will be less than in the higher elevations. A crust that has formed in the middle of this newest slab will make it harder to trigger any buried surface hoar that survived the rain and wet snow. We cannot rule out the potential for triggering slabs in this elevation band and it will be important to keep slope angles low until we see more signs of this layer becoming non-reactive.

Paying attention to what is above you, including other groups, when in this elevation band (bewteen 1,500-2,500′) will be important as avalanches initiated in the higher elevations could run into the mid elevations today.

Weather

Fri, December 19th, 2014

In the past 24 hours the precipitation has shut off and the temperatures have cooled – see table below. Winds have picked up slightly overnight along ridge tops and are averaging in the 20mph range out of the East at Sunburst this morning.

Today expect light snow showers with 2 € accumulation possible. Temperatures at 1,000′ will be in the high 20s to low 30s F range. Winds will be out of the Northeast at 10-20 mph.

The extended outlook is showing some potential for more precipitation as a complex series of Lows move through the Gulf and along the Aleutian chain over the next several days. There is a high level of uncertainty as to the timing and track of these systems with the next best chance for snow coming Sunday into the early part of next week.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	28	0	0	28
Summit Lake (1400′)	24	0	0	4
Alyeska Mid (1700′)	27	0	0	18.5

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	ENE	11	42
Seattle Ridge (2400′)	22	N/A	N/A	N/A

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
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

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