Turnagain Pass

The weather front that was only supposed to blow for one day (yesterday) and drop less than a foot of total snow, has been upgraded. The system is peaking this morning and forecasted snowfall totals have been increased to 12 – 18″ by tomorrow. Things are looking on track to hit that 18″ mark and snowfall as of 6am is in the 8-10″ range for both Girdwood and Turnagain Pass. Portage has around a foot and sadly, Summit Lake is being left out again with only what looks to be a trace.

The snow has been accompanied by strong east winds, beginning 30 hours ago. We can bet that wind slabs and cornices have been forming during that time and will continue to do so today as the wind should remain near 15-25mph with stronger gusts. To add to increased instability, check out the rapidly rising temperatures at Sunburst – over the last 30 hours temperatures have climbed their way from -4F to 20F… Mid elevations are seeing conditions as warm as 28F. That’s almost tropical.

Wind Slab avalanches and Cornice Falls are the main concerns today. These have likely been releasing naturally along ridgelines and it should be easy for us to trigger them if we get in the wrong spot. Remember that 2′ of fluffy powder from last weekend? The wind probably didn’t have much trouble blowing it around and this will only add to the size of new slabs. Furthermore, warming temperatures can make the snow ‘stickier’, aiding in wind slab and cornice development. These slabs are likely to be fairly soft and in the 1-3′ foot range pending the amount of sustained wind. They may also have the ability to overload those buried weak layers, which is a real concern discussed in Problem 2.

Storm slabs could also be forming in areas seeing 10″ or more of new snow. The storm is coming in ‘upside down’, meaning warmer snow over colder weak snow. This can create a slab/weak layer combo in the new snow. Storm slabs will only be as deep as the new snow, and should vary with location and elevation.

Similar to yesterday, if heading out be sure to:

• Watch for, and avoid, slopes that have been, or are being, wind loaded
  • New wind slabs are likely to avalanche easily
  • They could step down to buried weak layers, creating a larger avalanche
• Watch for stiffer snow over softer snow, cracking in the snow around you, or collapsing (whumpfing)
• Sticking to lower slope angles below treeline (below ~2,500′) and out of the wind will drastically reduce the chance for triggering an avalanche.

Graphics courtesy of the National Weather Service Anchorage Forecast Office.

Sunburst weather station (3,812′ elevation) at 6am, Nov 30th.

Triggering an avalanche breaking in weak snow, now hidden 2-3′ below the surface, is also a concern. This would be a larger avalanche than your typical wind slab and likely more dangerous. Whether or not this new load of snow, especially wind loaded slopes, will be enough to trigger these weak layers naturally, is a question. Add a person to the equation and the likelihood increases.

These are those layers of buried surface hoar and facets that formed in early to mid November and were causing grief last week when they were buried by 2-3′ of light snow. We know from last Saturday, when there were several remotely triggered slabs that occurred on Seattle Ridge and one remote triggered slab on Max’s in Girdwood Valley, that they are reactive in places.

If you are headed to those treed areas out of the wind, we still need to keep our guard up and look for any signs the loose snow is ‘slabbing up’. Warming temperatures alone could do this in areas that had no instability before. Both cracking and whumpfing, along with feeling the new and older snow with your boot or ski pole, to see if it has become stiffer or more cohesive will be good ways to assess the zone you are in.

Let us know if you’ve seen any glide avalanches lately. The last known glide crack that released was on Lipps SW face, sometime in the past week. These are clearly slowing down, but still, if you see a crack it’s never a good idea to hang out under it. They are unpredictable as to when they avalanche.