Tue, December 04, 2012 Turnagain Pass Avalanche Forecast

Tue, December 4th, 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

With unrelenting cold and calm weather, our shallow snowpack continues to degrade into weak, sugary snow exposing more rocks daily. At the upper elevations this process has been slower and a poor snowpack structure persists in certain areas, which is our primary concern. Though the only avalanche activity we have heard of or seen for the past 10 days has been sluffs in the weak snow, there is still a concern a slab could be triggered breaking in the old October facets near the ground.

Snowpack observations from yesterday from two notorious upper elevation starting zones point to a steady decline in the potential to trigger one of these slabs. The most concerning places to trigger a slide are those with little or no previous traffic. There are many slopes that remain untouched due to difficult early season/low snow cover access.

Snow surface conditions:
There is a very thin layer of dust on the snow surface that is believed to have been deposited sometime on Friday/Saturday by the strong winds channeled through the Mat-Su Valley. The high winds likely entrained particles that were then carried by the NW winds through Turnagain Arm and deposited in our forecast zone. The dust on snow became more visible with elevation yesterday.

Above treeline a scattered thin wind crust can be found on the loose snow surface in exposed areas. Below treeline there is still very loose, unsupportable snow which is sitting under some quite impressive surface hoar growth.

Sidenote: With the earthquake yesterday evening, I’m wondering (or more accurately hoping) if any facets were shaken off the slopes?

Weather

Tue, December 4th, 2012

Mid-level clouds moved in from the east yesterday associated with a multipart low pressure system spinning in the Gulf and even dropped a flake or two on Turnagain Pass. The clouds look to have reminded overnight and despite the cover, which helps to €œhold the heat in €, temperatures have decreased to a new seasonal low at all elevations, except sea level. Ridgetop weather stations are reporting -4 to 0F while treeline stations are -2 to 3F. The inversion is still firmly in place with sea level and valley bottoms in the -15 to -10F range. Expect clearing skies and temperatures to rise 5 degrees or so throughout the day. Ridgetop winds are luckily still light from the northeast, 2-5mph gusting 5-10mph, where they should remain today.

We are still waiting for snow and looking at the longer term model forecasts in hopes of seeing a €œfire hose € of moisture pointed at us. Unfortunately, we are going to have to keep waiting through the week – but it does look like there is hope for Saturday. It may not be the fire hose we want, but at least it is a substantial change in the pattern and we should finally see some precipitation.

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).

Kevin will issue the next advisory Wednesday morning, December 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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