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Mon, February 23rd, 2015 - 7:00AM
Tue, February 24th, 2015 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE in the Alpine and Treeline elevations today.   Dense slabs 1-3′ thick have the potential to release naturally on steep sunlit slopes in the Treeline elevations.   Slabs could also be human triggered anywhere from 2,000′ and above.   These slabs have the potential to propagate across large areas and carry, injure or bury a person.

Special Announcements

Iron those Carhartts, break out the sequins, and dust off the bolo €¦its Snowball time! Please join the Friends of the Chugach National Forest Avalanche Information Center and Alaska Avalanche School at Taproot for an €œAlaskan Formal € night at 7pm on February 27th.  You won’t want to miss this event!

Mon, February 23rd, 2015
Above 2,500'
3 - Considerable
Avalanche risk
3 - Considerable
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. Dangerous avalanche conditions. 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

A widespread layer of weak faceted snow sits anywhere from 1-3’ below the surface from 2,000′ and up.  Between 2,000’-3,000’, the aforementioned weak layer has proven to be the most reactive and slowest to “heal” or bond to the overlying slab.  Above 3,000’ that layer still exists and is still reactive

What this all boils down to is this: the likelihood of triggering a dry slab avalanche is highest in the 2,500-3,000’ elevation band.  The likelihood decreases only slightly as you gain elevation, but the consequences remain the same.  Slabs 1-3’ thick have the potential to be triggered by skiers and riders.  These slabs have the potential to propagate across slopes and entrain significant debris along the way.

Staying on terrain 35 degrees or less and avoiding the runout of steeper terrain above you is your best bet for avoiding this avalanche problem today.

Avalanche Problem 2
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

Sustained warm temps have helped to weaken slabs below the 2,500’ elevation.  Between 2,000-2,500’ sit slabs 1-3’ thick.  Those slabs are sitting on a layer of facets.  Yesterday we received multiple reports of groups experiencing collapsing in this elevation band where the slab has lost strength due to warming.

More recent slabs 6-12” thick that formed 3 days ago are sitting on a sun crust on steep South facing terrain.  Yesterday we observed two natural slab avalanches that released during the day in terrain with this setup (see photo).

Natural avalanche- Seattle Ridge – 2,400′ SE Aspect – Crown Depth estimate 1′.  photo: Fitzgerald

Seattle ridge natural Feb 22, 2015

These smaller slabs have the potential to step down to the deeper buried layer of facets.  

This combination of warm temps with slabs over a persistent weak layer is a perfect recipe for wet slab avalanches.  While the air temps are warm, it will be doubly important to pay attention to and avoid sunlit slopes with clearing skies later in the day.

Mon, February 23rd, 2015

A minor meltdown took place over the past 24 hours, with temperatures climbing into the high 30s to low 40s below 2,000′.   Winds were moderate out of the East in the morning and subsided by the afternoon.   Light rain fell up to 2,000′ with Alyeska Mid station picking up the most precip with .2 € of rain.

Today expect showery conditions, with the rain/snow line around 2,500′.   Precipitation amounts will be light, in the .1-.2 € range.   Winds will be out of the East at 5-10 mph.   Temperatures will climb slightly again, with 40 degrees expected at the 1,000′ level.   Cloud cover will gradually diminish by the evening hours.

The extended outlook is calling for generally drier conditions.   A low pressure system will brush by the area on Wednesday bringing only a slight chance for precip.   Temperatures will cool as we move into the middle part of the week.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 37 rain .1 41
Summit Lake (1400′) 37 rain .1 7
Alyeska Mid (1700′) 37 rain .2 22

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 29 n/a n/a n/a
Seattle Ridge (2400′) 31 n/a 18 44
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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.