|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.
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 Slab: Winds 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 snow: Sluffing 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.
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.
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.
|Observation: Bertha Creek
|Schauer/ Cullen Forecaster
|Observation: Magnum & Cornbiscuit
|Moderow / St. Clair
|Observation: Tincan Backdoor
|APU Snow Science I
|Observation: Silvertip Creek
|Observation: Seattle Ridge
|John Sykes Forecaster
|Observation: Kickstep NE Bowl
|Observation: TinCan Backdoor/ Center Ridge
|AAS L1 Turnagain
|Avalanche: Lynx Creek
|Observation: Turnagain, Seattle, Mt Ascension
|Silverton Mountain Guides