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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, December 21st, 2012 - 7:00AM
Expires
Sat, December 22nd, 2012 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

A MODERATE danger continues today above treeline on previously wind loaded slopes steeper than 35 degrees where the possibility still remains for a person to trigger a slab avalanche. The most likely places to find and release one of these old persistent slabs are on slopes harboring stiff and hollow feeling snow – supportable to a person or snowmachine. Below treeline and areas above treeline where these stiff old slabs do not exist there is a LOW danger.

Fri, December 21st, 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
  • 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

As the Mayan Calendar predicted the end of the world at 2:11 this morning and along with that the end of our meager early season, it seems neither has occurred. The world is still here and so is our shallow snowpack full of persistent weak layers.

The wind slabs that caused so much excitement a week ago have been slowly deteriorating under the cold and clear weather to the point of becoming mostly non-reactive. Snowpack evaluations and the lack of recent avalanches have pointed to a pack that is becoming harder and harder to trigger an avalanche in. However, this is not the case everywhere and we struck gold, as John Fitzgerald stated in his observation, yesterday with finding one of these slopes still flashing red lights.

The areas we are most concerned about are in steeper, unsupported terrain (i.e., above cliffs and on rollovers at the mid-elevations) where stiffer, supportable snow (old wind slabs) are sitting on weak sugary snow. Watching and listening for collapsing and hollow feeling areas will be your best bet at sussing out suspect slopes. If you can punch a pole or boot though the stiff snow, though this may be tough in thicker slabs, and feel unconsolidated snow beneath – steer clear and head for a slope lacking that stiff slab.

Weather
Fri, December 21st, 2012

The SEVERE CLEAR weather conditions will continue to dominate for another couple days. The strong inversion has temperatures at sea level and in the parking lots at Turnagain Pass near -20F. The good news is the temps have jumped to the balmy mid-teens on the ridgetops this morning, where they should remain. Winds have backed to an easterly direction overnight and will pick up to the 10-15mph range, gusting to 30mph, today.

The well entrenched, and not so loved, ridge of high pressure looks to start breaking down near the end of the weekend. Models are hinting at a little precipitation around Monday with a weak low pressure system developing the in Gulf. However, mid-week next week a larger low pressure moving into the Bering will hopefully bring a decent shot of precipitation €“ though this is too far out to say for certain €¦

Happy winter solstice!   A little comparison with last year’s solstice:   (Turnagain Pass SNOTEL, 1880′)

                                                                                      Dec 21, 2012                                               Dec 21, 2011
Snow depth                                                 25 €                                                                                 78 €
Seasonal snowfall                       35 €                                                                                 129 €
Seasonal water                                   3.4 €                                                                               13.4 €

Roughly a quarter of where we were last season at this time €“ oh grim.


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 Saturday morning, December 22nd.

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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.