Turnagain Pass Avalanche Forecast

It’s been just over a day since the end of the last storm that hit Sunday into Monday, which dropped 2-3′ of new snow. With light snow showers forecast today, possibly adding 3-5 inches and even another 2-4″ tonight, this should not be quite enough to create new avalanche issues in itself and the main concern still lies with the snow that fell early this week.

Large storm slab avalanches are possible. These are in the 1-2 foot thick range depending on the amount of new snow in Turnagain Pass and up to 3′ thick in favored areas in the upper Girdwood Valley where more snow fell. Although we have little information from yesterday, we know these storm slabs were touchy on Monday. This is in large part due to the snow being warmer and heavier as well as falling onto 4-10″ of loose faceting snow with surface hoar on top. In areas up to 2,500′ that loose snow sat on a stout crust. Yesterday, observers in the 2,000-2,500′ elevation band on Seattle Ridge found the storm slabs to be bonding, a great sign, but this isn’t something to assume is happening everywhere just yet. It’s a day to really watch for RED FLAGS:

• Any whumpfing in the snowpack?
• Cracks that shoot out in the snow around you?
• If yes, then the new snow is still unstable and sticking to low angle slopes and the flats is key.

Wind Slabs:  Ridgetop winds have been steady on Sunburst right around 15mph with gusts into the 20’s mph, from the east. This is just enough to keep any snow that is still available for transport along ridgelines moving and fresh wind slabs may be found in the Alpine. Add to that, we should be on the lookout for any older wind slabs from the Sunday/Monday storm in the Treeline and Alpine elevation bands.

Cornices:  Although visibility has been difficult, we know cornices have grown and could still be teetering on the brink. Give them a wide berth as they can now easily break further back than we might expect. As seen last week, they can also trigger an avalanche below, creating a bigger problem if a person is involved.

Seattle Ridge at 2,000′: There is around 20″ (50cm) of settled storm snow from the Sunday/Monday storm. This fell on top of another foot (30cm) of older snow that had become faceted with the cold and clear weather during the end of last week. No signs of instability were seen in this pit yesterday (12.8) and the crust, formed when rain fell up to 2,500′ on 12.1, sits ~32″ (80cm) below the surface. Photo: Brian Murphy

That old October snow near the ground is getting more and more buried with the snowy weather. This is great news! It helps to squash the layer and keep our weight far above it; in essence making it so triggering a deep persistent slab is much less likely. That said, hitting a thin area in the snowpack or traveling in areas with an overall shallower snowpack (around 3-4′) is still concerning for triggering a large slab. The south end of Turnagain Pass through Silvertip, Johnson Pass and Summit Lake all have slopes without as much snow as Turnagain or Girdwood. Heads up in these areas and remember to feel/listen for whumpfing and watch those shallow slopes.

An example of an area that is still suspect for triggering a deep slab. This is pit is from Tenderfoot Ridge in the Summit Lake area (2,500′ elevation) and shows the weak facets at the bottom of the snowpack. 12.8.20. Photo: Nick D’Alessio