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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, December 2nd, 2014 - 7:00AM
Expires
Wed, December 3rd, 2014 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche danger is MODERATE today in the alpine, where newly formed wind slabs up to 10 € in depth will be easy to trigger on steep leeward slopes.   At treeline the danger is LOW, with the exception of isolated wind loaded pockets in steep terrain.   Below treeline the snowpack is still too shallow to warrant a danger rating.

Early season hazards such as shallowly buried rocks, stumps and small glide cracks require careful travel, especially below treeline.

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The next advisory will be Thursday Dec 4th at 7am.

Avalanche Outlook for Wednesday: Expect wind slabs to continue to build at a modest rate through Wednesday.   A pattern of unsettled weather will bring some additional light snowfall and enough wind to keep the danger at MODERATE in the alpine for Wednesday.

Special Announcements

Our first, in a series of four,  Fireside Chats begins Thursday December 4th! These will be held in both Girdwood and Anchorage. Thursday night’s Chat will be at 6:30pm at the Glacier Ranger Station in Girdwood. The topic will be –  Intro to Avalanches: Terrain and route finding,  presented by CNFAIC forecaster John Fitzgerald. Mark your calendar!

Tue, December 2nd, 2014
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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

A modest amount of new snow combined with older low density snow and steady winds out of the East/Southeast have formed wind slabs on leeward aspects.  These slabs will be sensitive to human triggers and will be up to 10” in depth.  Expect them to be easiest to trigger as they are forming.  Keep in mind that while the predominant winds have been out of the East, wind changes direction as it interacts with terrain.  Your best bet is to be on the lookout for shooting cracks in the snow, upside down snow, or surfaces that are smooth and pillowy.  These are signs of recently formed wind slab.  Avoiding these wind loaded areas, especially in terrain over 35 degrees will be the best way to manage this avalanche problem today.

Weather
Tue, December 2nd, 2014

A large Low pressure system centered in the Bering Sea that has made its way eastward along the Aleutians has brought with it precip and winds to the mountains around Eastern Turnagain Arm.   Snowfall amounts have been greater to the West and less on Turnagain Pass.   Weather station data from the Girdwood Valley is currently unavailable.

A warm front associated with this Low has brought slightly warmer air over the area this morning.   Fortunately temps have remained cool enough to keep the precip in the form of snow. As this frontal boundary passes expect temperatures to cool and light snow to continue into the daytime hours.

Today we can expect another 3-5 inches of snow.   Temperatures at 1,000′ will be in the low 30s F.   Ridge top winds will be in the 10-20 mph range.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 25  2  .2  20
Summit Lake (1400′)  24  3  .3  5
Alyeska Mid (1700′)  n/a  n/a  n/a  n/a

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  19  E  13  30
Seattle Ridge (2400′)  21  SE  18  37
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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.