Turnagain Pass

There were no new observations that came in yesterday. On Thursday there were several observations of small to large wet loose avalanches and a small wet slab that released on Penguin ridge during the warm and sunny afternoon.

A potent storm system will impact the forecast area today, bringing strong winds and snowfall across the region. Coastal areas, like Portage and Placer, are expected to see the heaviest precipitation with weather models predicting up to 2.5″ of water which could be 2-3′ of new snow at upper elevations. Slightly more inland locations, like Girdwood and Turnagain Pass, are expected to see less precipitation with 0.5-1.0″ of water or roughly 6-12″ of new snowfall expected above 1000′. Strong winds are expected throughout the day, with wind speeds peaking this afternoon at averages of 40-60 mph and gusts possible up to 75 mph out of the east. Rain line will rise to roughly 800′ this afternoon.

If the weather forecast is correct and coastal areas actually see 2-3′ of new snow today very large natural and human triggered avalanches will be very likely. We recommend avoiding all avalanche terrain in these areas, including runout zones from overhead avalanche paths. 

For the more inland portions of the forecast zone natural and human triggered avalanches will still be likely and the potential size of avalanches will depend on the amount of new snow we get today. If there is 10-12″ or more of new snow on the surface then storm slab avalanches within the new snow will be possible even in wind sheltered areas. Wind slabs 1-2′ deep will also be forming and are likely to cause natural or human triggered avalanches at upper elevations, especially along ridgelines, gullies, and near convex rolls. To assess how sensitive storm slab or wind slab avalanches are to human triggering you can use hand pits and small test slopes to evaluate how well the new snow is bonding to the old snow surface. Below 2500′ the new snow is likely to be falling on a melt freeze crust that formed on Thursday night, which may mean that it does not bond well with the old snow surface. We recommend a cautious approach avalanche terrain today and carefully evaluating the new snow before entering steep slopes.

Snowfall forecast for Saturday at 4am through Sunday at 4am, with coastal areas strongly favored for higher snow totals. Graphic courtesy of NWS Anchorage 3.30.24

Below 1000′ we are expecting the precipitation to switch to rain by this afternoon, which will make wet avalanches possible on steep slopes. Warm temperatures and rain at low elevation over the past week have formed a thick layer of wet snow on the surface, which could cause wet loose avalanches to be larger than typical today. This type of avalanche tends to start out small, but they can grow quickly as they run down slope and create surprisingly large and destructive avalanches. Common hiking areas like the Byron glacier trail in Portage can easily be struck by this type of avalanche and we recommend avoiding these hiking areas with overhead avalanche paths today.

Large wet loose avalanche from earlier in the week in the Seattle Ridge area. Photo from Jay Liska 3.28.24

Buried about 1-3′ deep in the snowpack there are a few different weak layers that we are still monitoring which formed in early March. These weak layers caused a widespread cycle of human triggered avalanches two weeks ago, and the new snow and wind today will add stress to these layers and make them more likely to cause larger avalanches. Based on our recent field observations the weak layers have gained a lot of strength since their active period two weeks ago, but we want to be aware of the outside chance for a very large avalanche to occur on one of these persistent weak layers. The best way to mitigate this problem is to give the weak layers some time to adjust to the new snow load and keep a conservative mindset today by sticking to low angle terrain.