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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, December 16th, 2012 - 7:00AM
Expires
Mon, December 17th, 2012 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

ANNOUNCEMENTS
We would like to send a HUGE thank you to BRP and AMDS as a brand new 2013 Ski Doo REV-XM 800cc snowmachine was granted to the Friends of the CNFAIC through a generous loaner program. As a longtime supporter of the avalanche center, AMDS recommended this machine to benefit the entire backcountry community. Thanks also to the folks who joined us in the opening of the Turnagain Pass motorized area for the unveiling of the new sled and an avalanche condition synopsis!

BOTTOM LINE
We continue to have a MODERATE avalanche danger above treeline for lingering wind slab avalanches. These have been releasing on all aspects and yesterday three people were able to trigger three slides (see below). The MODERATE danger we are dealing with today is a:   low probability with high consequence situation – the larger the terrain, the larger the avalanche possible. This is a good thing to keep in mind with the variable snow conditions, size of the slabs and terrain you are riding in. Below treeline there is a LOW danger due to the lack of a slab.

Sun, December 16th, 2012
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
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
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

There were three wind slab avalanches triggered by skiers/snowboarders yesterday. Two on the Sunburst SW aspect on a wind loaded rollover and one on a westerly aspect of Tincan. All were between 2,700’ and 3,000’ in elevation and were small to medium in size – a few more details HERE. We have also had more reports and photos come in of older natural wind slabs that were likely triggered Thursday morning (Todd’s Run, N shoulder of Tincan Ridge and SW Sunburst).

During the past week we have had moderate to strong winds from all directions that have created an extremely variable snowpack. The riding conditions are not something to write home about and neither are the avalanche conditions. Areas that are scoured to the rocks sit right next to wind loaded slabs with the potential to release.

Good travel practices and thoughtful terrain management are key – a few important ones for today:

1-      Expose only one person at time
2-      Watch for recent avalanches
3-      Don’t discount collapsing and whumphing

Avalanche Problem 2
  • Persistent Slabs
    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

The slabs mentioned above are taking a long time to heal because they are sitting on weak faceted snow formed during the November/early December cold spell. Faceted snow is very tricky and there is way too much of it in our pack. It can become dormant for a while once the pack adjusts to a new load, then with a little wind or snow, rear its head – this is pretty much what we have seen this season so far. Just remember when you are dealing with facets and persistent weak layers (including surface hoar) they are “guilty until proven innocent”.

Below treeline the snowpack has been sheltered from the wind and has broken down to becoming one unconsolidated unit. There are a multitude of weak layers but there is not a slab on top.

Weather
Sun, December 16th, 2012

Temperatures have PLUMETED to a new seasonal low on the ridgetops. Sunburst and Seattle Ridge have dipped to -5F and -3F this morning where they are expected to increase only a few degrees today. There is not much of an inversion as sea level and parking lot temperatures hover between 5F and -10F. The light NW winds that were near 10mph overnight look to pick up to the 25mph range by this afternoon which should keep things feeling quite cold.

Our hopes for more snow this week is diminishing as the low pressure system moving into the Gulf on Tuesday looks to dig further south and just brush our neck of the woods. We could get a few flurries that spill over but stay tuned in case things change in our favor.

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).  

Graham will issue the next advisory Monday morning, December 17th.

Observations
Recent Observations for Turnagain Pass
Date Region Location Observer
11/27/23 Turnagain Avalanche: Tincan Ridge Schauer/ Stiassny Forecaster
11/26/23 Turnagain Observation: Road report: Slide with dirt on Repeat offender Anonymous
11/26/23 Turnagain Observation: Pete’s North Ben Sullender
11/25/23 Turnagain Observation: Tincan trees John Sykes Forecaster
11/21/23 Observation: Spokane Creek John Sykes Forecaster
11/20/23 Turnagain Observation: Sunburst Anonymous
11/19/23 Turnagain Observation: Magnum – PMS Bowl Schauer/ Cullen/ Jonas Forecaster
11/19/23 Other Regions Observation: Sunnyside/Penguin Jose Ramos-Leon
11/19/23 Turnagain Observation: Eddies Andy Moderow
11/19/23 Turnagain Observation: Cornbiscuit Anonymous
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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.
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