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Sun, December 15th, 2013 - 7:00AM
Mon, December 16th, 2013 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

With 2 days of new snow and wind, we have a  MODERATE  avalanche danger for wind slab and loose snow avalanches. Wind slabs 1-2+’ deep will be possible for a person to trigger on upper elevation slopes over 35 degrees. Watch for any area where the wind has blown the new snow into drifts and slabs €“ most likely just off ridgelines and rollovers. Otherwise, sluffing in the new light snow should be expected.

*Check out the storm totals below in the Mountain Weather section.

Special Announcements

A reminder that all motorized  areas on the CNF remain closed in order to prevent resource damage – snow depth is increasing but still insufficient.

Sun, December 15th, 2013
Above 2,500'
2 - Moderate
Avalanche risk
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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

Wind slab avalanches will be the most concerning avalanche problem today. With storm totals upwards of 15-18″ these are expected to be 1-2+’ deep, soft and potentially quite sensitive to human triggers. They are most likely to be found on slopes over 35 degrees just off ridgelines, on rollovers and the side-walls of gullies. Keep an eye out for any slope with signs of recent wind loading – this means areas with stiffer snow over weaker snow, smooth rounded surfaces and hollow feeling snow.

Though the wind died down in most locations yesterday afternoon, it was blowing moderately to strong from the east early in the day yesterday. Though any natural activity has likely ceased, I’m expecting there are some good sized wind slabs that are still fresh enough to cause problems for people. If the visibility breaks enough for travel to the more exposed terrain, finding a 2’ deep unmanageable wind slab is not out of the question.

Below is a poor image of a few small wind slab avalanches on Tincan yesterday (human triggered 2,500′, W aspect). It is still uncertain how the upper elevation wind affected slopes are handling this new load. More on yesterday HERE and HERE.

How is the early December crust behaving?
The new snow did fall on a ~¼” breakable crust which had, in places, surface hoar on top. Though this interface was showing a fairly good bond yesterday, I would not count out that avalanches could be larger and run further with this crust providing a slippery bed surface and the added uncertainty of the now buried surface hoar.

Avalanche Problem 2
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

It will be mostly a sluff management day. With decreasing temperature and generally calm to light winds, much of the new snow will be in a very loose unconsolidated state (‘cold smoke’?) and initiating a loose snow avalanche will be likely. In continuously steep, channeled terrain expect sluffs to gain in volume, run fairly far and become more of a concern.

Sun, December 15th, 2013

24-hour snowfall totals (6am Saturday to 6am Sunday):

  • Turnagain Pass SNOTEL: 9 € (0.5 € water equivalent, 5.5% density-dang…)
  • Summit Creek SNOTEL: 3 €   (0.2 € water eq., 6.67%)
  • Girdwood Valley: ~6 € (0.4 € water eq., 6.7%) *not all Girdwood Valley stations reporting – rough estimate.

 Storm totals are (8am Friday to 6am Sunday €“ past 46 hours):

  • Turnagain Pass: 17 €  (1 € water equivalent, 5.9% density)
  • Summit Creek SNOTEL: 8 €    (0.5 water eq., 6.25%)
  • Girdwood Valley: ~15 €    (~1 € water eq., 6.7%)

Currently, light snowfall continues in the Eastern Turnagain Arm which may add another inch this morning. The easterly wind that averaged 20-30mph with gusts to the 50’s yesterday morning has decreased to the 5-10mph range and backed to the north. Temperature has dropped from the 20’s to the single digits overnight.

Today, skies should slowly break and snow showers taper off as the low pressure over us heads east and colder drier air moves in. Wind looks to remain light, 5mph, from the north and temperature remain in the single digits to low teens at most locations.

Tomorrow and Tuesday look to be clear and cold before another system moves in Wednesday/Thursday. It looks like winter is arriving!

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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.