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Thu, February 14th, 2013 - 7:00AM
Fri, February 15th, 2013 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

New snow and wind overnight, with more on the way today, will ratchet our avalanche danger to CONSIDERABLE above treeline and MODERATE below treeline. By this afternoon, we should see 12-20 € of new snow accompanied by strong easterly winds at the upper elevations. All types of storm snow avalanches are out there today:  Wind slabs in all areas with recent wind deposited snow, storm slabs in areas out of the wind and loose snow sluffing. There is also a potential for avalanches to break 1-3′ deep in the existing pack, making for a larger and more dangerous slide.

Expert level route finding skills and keeping slope angles below 35 degrees is recommended – this includes slopes above or adjacent to you.

Special Announcements

Stop by the motorized lot this Friday at 11AM! Join CNFAIC forecasters and Gold Level sponsor AMDS for an avalanche awareness event and memorial snowmachine ride on the 5th anniversary of this fatal avalanche in Turnagain pass.  


Thu, February 14th, 2013
Above 2,500'
3 - Considerable
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
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Today will be one of those classic storm days – maybe not in the gnarly Chugach storm category, but it definitely has enough punch to spice up the avalanche conditions. We have had 6″ of new snow at treeline overnight, which often translates to 8-10” at the upper elevations. With the addition of the same today, we are looking at between 1 and 2 feet of new snow in just under 24 hours. This is all being blown around by quite strong easterly winds (averaging 40mph, gusting 70mph). That said, it’s a text book case for storm snow avalanches:

Wind SlabWinds will be moving the snow around and loading slopes during the day. These slabs will be in the 1-4’ range and naturals are possible. Though wind slabs formed yesterday were quite stubborn due to the mild temperatures, don’t count on that today. Despite the mild temps, things are loading quickly and could be quite touchy regardless.

Storm Slab:  The new snow looks to be coming in slightly upside down. This can create a slab/weak layer combo in the storm snow and produce slab avalanches even out of the wind. This may or may not be an issue today, but it’s good to keep in mind.

Loose snowSluffing in the new snow should be prevalent and easy to initiate by a person.

Cornices:  These continue to grow and calve with each storm in the past couple weeks of warmer temperatures.

Below treeline:  Watch for winds that could possibly penetrate and load rollovers below treeline. Also, a series of crusts begin 6-12” below the existing loose snow.  This could act as a bed surface if enough weight overloads the snow at the top of the crust. Digging in with your hand and seeing how well the snow is sticking to the crust is always a good idea.

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

For the past few days we have been talking about a couple mid-pack crusts (1.5-3’ deep) and the weak snow that surrounds them. There are two in particular, one formed January 21-23 and the other January 30. These exist up to ~2,800’ – give or take depending on location. This facet/crust “sandwich” is disconcerting and has shown its head in the Girdwood Valley with a very large class 3 avalanche triggered Monday 2/11 in the Winner Creek area. We have been following these layers in the Turnagain zone since they were buried and they have shown little evidence to be a problem (no avalache activity/scary pit results) – yet…  This may be changing as we are now seeing some propagation propensity as Fitz found yesterday. In the pits my party dug, one out of three was concerning.

With today’s rapid loading, we could possibly see avalanches break to these weak layers and bed surfaces. We could also potentially see new snow avalanches step down and trigger them. Today could be a good test.

Thu, February 14th, 2013

Yesterday’s mild and overcast weather turned a bit obscured, windy and snowy as a quick hitting system moved through last night. Since yesterday afternoon we have picked up 6 € of snow on Turnagain Pass and similar amounts in the Girdwood Valley. Summit Lake squeaked out a mere inch or two €“ but more is on the way! East winds have been strong, averaging 30-40mph with gusts over 70mph since 4pm yesterday. Temperatures have climbed a degree or two since midnight to 30F at 2,000′ and the low 20’s ~3,500′.

Another low pressure system is moving in currently, right on the heels of last night’s event, and should add an additional 6″ at treeline. This will bump the strong east winds up even higher today with expected averages ~40mph and gusts to over 70mph. Temperature should hover around 30F at 1,000′ and the low 20’s on the ridgetops. The rain/snow line is expected to remain around sea level to 300′.

Tomorrow this system slowly moves out. Instability showers may add another few inches of colder snow as winds shift to a more SW direction. Saturday looks as though skies could break to some degree as we should be between storms.

Fitz will issue the next advisory tomorrow morning, February 15th.

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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.