Turnagain Pass

Winds picked up late in the day yesterday, with sustained speeds around 15 mph and gusts to 25 mph at ridgetops since around 5 p.m. With around 6-12″ of soft snow near the surface prior to the bump in winds, we already had plenty of loose snow available for slab building, and we are expecting to get some more snow this morning before skies start to clear up in the afternoon. The storm is expected to head to the north of us, leaving Turnagain Pass with only a few inches of new snow but possibly bringing heavy snowfall towards the north end of the Girdwood valley. We saw large natural and human-triggered avalanches on Raggedtop (details here, here and here) during both of the last two storm events, and similar activity is likely today if the storm delivers. The stakes are a little bit higher even for relatively smaller wind slab avalanches, which could step down to one of several persistent weak layers in the upper 3′ of the snowpack (see problem 2 below), resulting in a larger avalanche.

Safe travel today will require being aware of changing conditions as the storm moves through. The increase in danger will depend partly on the amount of new snow we get, but the increased winds will be enough to create sensitive slabs near ridgelines, below convexities, and in cross-loaded gullies. Be on the lookout for our typical signs of instability- shooting cracks, collapsing, and recent avalanche activity. Today’s active weather will require cautious route-finding, especially at higher elevations.

This slope on Raggedtop has slid three times following recent snow and winds. We are anticipating similar activity today, especially towards the north end of the Girdwood valley. Photo: George Creighton, 04.01.2021.

Loose snow avalanches: Steep slopes that have been sheltered from the wind have up to a foot of loose snow sitting on top of firm surfaces. It will be easy to trigger dry loose avalanches (sluffs) today, and they can pick up enough volume and speed to carry a person. If the sun comes out later in the day, we will likely see some wet loose activity as well. While it is unlikely they will be big enough to bury you, they can be dangerous if they drag you into terrain traps like cliffs, trees, rocks, or gullies.

In addition to the problems related to new and wind-transported snow mentioned above, we are still dealing with multiple persistent weak layers in the upper snowpack. We continue to find layers of buried surface hoar and near-surface facets in the upper 3′ of the snowpack, and although they are becoming more stubborn it is still possible to trigger an avalanche on these layers. With new snow and winds at upper elevations, and a mix of wet snow and rain falling on a wet surface at low elevations, these layers may be a little more sensitive today.

The most likely places to trigger an avalanche on this layer are the same as those mentioned in problem 1 above- steep slopes near ridgelines, convexities, and mid-slope gullies. Freshly wind-loaded slopes are most suspect, but it will also be important to remember that slopes that have been previously wind-loaded will also be likely spots to trigger an avalanche on these weak layers.