Turnagain Pass

We do not yet know the extent of avalanche activity from the stormy weather yesterday, or last night. However, we can expect storm snow avalanches were occurring to some degree. These would most likely be wind slabs at the higher elevations and sluffs in the new snow in steep terrain.

Marvelous March begins with a bang. Not only do we have 10 hours and 24 minutes of daylight today, a storm system just brought a dose of very light (low density) powder snow. The storm looks to taper off today, only adding a couple more inches of snow. Here are the estimated snow amounts:

Estimated snowfall totals
Girdwood Valley: 6-10″
Portage Valley:  10-14″
Turnagain Pass:  6-10″
Summit Lake:  4-6″

It looks as though the winds will again be a large player in avalanche issues. They were easterly during the storm, but as of 6am began a shift to the northwest where they should blow in the 20-30mph range with stronger gusts. It won’t take much wind to blow all the loose new snow around, creating fresh wind slabs. Another player is the new/old snow interface. The new snow has fallen on various layers of loose faceted snow, wind crusts and sun crusts. All these layers will keep the snow from bonding right away so that will make wind slabs and storm slabs that much easier to trigger. The good news is, we should be able to see all these issues as they are ‘surface instabilities’ related to the storm snow and wind loading.

Wind Slabs:  Not only are there wind slabs left over from the storm when the winds were easterly, but new slabs forming with today’s NW winds on different aspects are also a concern. They are most likely found above treeline or in exposed areas in the trees that saw, or are seeing, wind loading. Watching for areas where winds are affecting the snow will be key, along with feeling for stiffer snow over softer snow or seeing cracks that shoot out from us.

Storm Slabs:  On slopes out of the wind we could trigger shallow storm slabs. These would be the depth of the new snow, so not on the smaller side. Because the old snow surface was a mix of facets and crusts, we are expecting poor bonding with the new snow. If the new snow is too loose, then we may not see storm slabs. But as the snow settles, these could become an issue in the future; something to look for.

Loose Snow Avalanches:  Sluffs again should be easy to trigger and could run further than expected. They could gain a lot of volume in areas that saw higher snow amounts.

Cornices:  With the new snow and winds, chunks of cornices can fall naturally and trigger sluffs or slabs below. Once travel becomes possible along ridgelines, remember to give them an extra wide margin.

It is still snowing in Portage Valley. Conditions at 5:30 this morning along the Seward Highway at the Portage Valley curve (MP 78.9). Image from the AK DOT & PF’s RWIS road weather cameras. 

Buried in the top 3′ or so of the snowpack are various old layers of facets and buried surface hoar. These layers have shown themselves to be unreactive, meaning triggering an avalanche in one of them is unlikely. However, once skies clear enough to take stock of the avalanche activity that occurred during the storm, we’ll be looking to see if any storm snow avalanches stepped down into these various layers. This would produce a larger slide and tell us a layer has again become reactive. The storm didn’t have a lot of water weight to add much stress to the old layers as the snow was so light, so we are not expecting any step down avalanches, but there can always be surprises out there.