Turnagain Pass

Warm temperatures and cloudy skies have brought the onset of the spring shed cycle to our region, with the first known observation of a large wet slab avalanche coming out of Portage along with many glide avalanches across the forecast area. Coastal areas, like Portage, have seen about 1.5″ of water over the past few days which fell as rain below roughly 2000′. This rapid additional of water to the snowpack creates prime conditions for wet slab avalanches to start releasing. The large wet slab below was observed on a NW aspect at 1400′ near Explorer Glacier in Portage and released naturally sometime on Sunday night or Monday morning.

First proper wet slab of the spring shed cycle, with the crown up to 6′ deep. Photo 4.22.24

A small section of this glide avalanche released naturally on the S face of Cornbiscuit with much more snow waiting to come down. Photo from Anonymous 4.21.24

Cloudy skies and warm temperatures last night likely prevented a solid refreeze of the wet snow on the surface. After multiple days of warm and cloudy weather the snowpack has rapidly transitioned to springtime conditions and large wet slab avalanches are likely, especially near the coast where an additional 1.5″ of rain over the past few days has weakened the snowpack even more. Wet slab avalanches are very difficult to predict in terms of location, but the timing for wet slabs is prime right now after several days without a solid freeze. These avalanches can be very large and destructive and tend to release naturally once the melt water moving through the snowpack causes existing weak layers to loose strength.

Near the Crow Pass Trail yesterday we found a concerning weak layer about 1′ above the ground where the melt water from the surface was pooling on top of a layer of basal facets from early in the season. The exact depth and weak layer that wet slabs release on is likely to vary across the forecast area depending on the existing snowpack structure. We recommend carefully evaluating the snow surface conditions and avoiding steep slopes where the surface snow has melted and there is water actively moving through the snowpack. To avoid this problem you could try to access higher elevation northern aspects where the snowpack still consists of mostly dry snow.

Wet loose avalanches are also likely today, and can be a precursor to wet slab activity. These are easy to trigger on any steep slope once the snow surface has melted. The size of wet loose avalanches depends on the depth of the wet snow on the surface and the size of slope that the avalanche runs down. These are typically small avalanches but can grow very large under the right conditions.

Glide Avalanches are also releasing naturally and can be very large and destructive. If you can see a glide crack on the slope it is best to avoid spending time underneath because they can release randomly.

Cornice Fall is also likely as the sun weakens the snowpack’s connection with the underlying ridgelines. When cornices are receiving direct sun it is best to avoid being underneath them and give them a wide berth if you are travelling along a ridgeline.

Wet loose avalanche debris along the road to the Crow Pass Trailhead containing some very large chunks of wet snow. Photo 4.22.24

There are some lingering persistent weak layers in the snowpack from earlier in April and late March which could cause an outlier avalanche, especially in steep terrain on northern aspects at upper elevations. These layers do not seem to be very widespread but it would be easy to be caught off guard by a persistent weak layer if you are in the springtime mentality and expecting stable snow conditions. If you are trying to access this kind of terrain we recommend digging a pit to evaluate the snowpack structure and look for suspicious weak layers with stability tests before committing to steep terrain.