Sun, November 25, 2012 Turnagain Pass Avalanche Forecast

Sun, November 25th, 2012

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

It was a quiet day in the backcountry yesterday with no slab avalanche activity reported. Though we are starting to see some sluffing in the loose facets in very steep rocky terrain. The snow surface conditions in most areas consist of loose recycled powder with 1-3cm surface hoar on top.

As far as our snowpack situation and the “persistent slab” problem goes, it continues to be a concern. Though the slab is slowly deteriorating into one large weak layer with cold, clear and calm weather there are still places at the upper elevations that have the potential to avalanche. We found one such area yesterday in the Turnagain Pass region where pit results pointed to instability on a suspect slope containing the slab/weak layer combo. What we are finding is that there are slabs that still have the potential to propagate but triggering them is becoming more difficult. A video and more details of our field day HERE.

Slopes that are most suspect to avalanche are those in the 40 degree range and unsupported from below. These slopes are also not the most enticing due to thin coverage. Using a pole to feel the snowpack structure and watching for collapsing (whoomphing) and cracking will be your best clues to suss out this poor structure.

Other observations that have come in from surrounding areas show current instability as well as future weak layers when we get our next bout of snow. One from the Girdwood Valley and one from the Lost Lake area near Seward.

Below treeline we continue to see a snowpack that is rotting away with the cold and consists of faceted snow with a degrading crust ~10” deep. Where slopes are steep enough, initiating sluffs in the loose facets is possible.

The image below is an avalanche incident rose from Nov 2^nd (first snowfall on the October facets) to present, Nov, 24^th. The rose shows aspect and elevation of all avalanches (both natural and human triggered) we have recorded. We feel all of these slides broke in the October snow. The last avalanche reported was the Sunburst natural on Nov 21^st / 22^nd.

Weather

Sun, November 25th, 2012

Single digit temperatures are locked in at the lower elevations and parking lots and look to remain this way for several more days. At just 2000′ however, temps are up to 20F and in the high teens on the peaks. This is quite the inversion. The easterly winds that have remained very light did bump up slightly last night (~15mph) on the ridgetops. The winds are back down to ~5mph this morning where they are likely to stay. No precip is forecast for several days…

Though there are a few small low pressure systems in the Gulf, they are not impacting our region – what we need is a large scale pattern shift and the removal of the blocking high pressure over mainland Alaska. Hopefully we will see this later this coming week.

This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).

I will issue the next advisory Tuesday morning, November 27th.

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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