Turnagain Pass

Several new avalanche observations came in yesterday from the Portage and Skookum valleys, but as far as we know they were all avalanches that released earlier in the week. Likely most of them released naturally during the quick hitting storm on Tuesday night into Wednesday. There is a concerning pattern of avalanches releasing with much wider start zones than typical, which is a strong indication of a persistent weak layer.

Natural avalanche near Explorer Glacier that likely released during the storm on Tuesday night. Photo from Emily Sullivan 3.8.24

The storm that brought about 1′ of new snow to Turnagain Pass and closer to 2′ of new snow to Placer Valley on Tuesday night buried a weak layer of facets. At elevations below about 2000′-2500′ there is an icy crust which formed on Presidents Day associated with the layer of facets, which has caused avalanches failing on this layer to release much wider than normal, connecting multiple terrain features and creating large avalanches. Due to the icy crust at these lower elevations this layer of facets is likely to remain unstable for longer than normal and could produce additional large avalanches. Above 2500′ the new snow fell onto a mix of firm wind affected and softer snow surfaces, which initially did not bond well with the new snow. We are uncertain how long the instability at the interface with the new snow from this week will last at upper elevations.

It has been three days since the last storm, so the snowpack should be adjusting to the new snow load, making human triggered avalanches 1-2′ deep less likely. However, persistent weak layers can remain unstable for longer than normal and cause large avalanches without obvious warning signs. We recommend carefully evaluating how well the new snow is bonding to the old snow surface before committing to steep terrain.  Since the weak layer is only buried 1-2′ deep right now, using hand pits and jumping on test slopes are still viable options to evaluate the interface with the old snow surface. If you want to avoid this problem entirely we recommend sticking to low angle slopes.

Dry loose avalanches (aka sluffs) are very likely on steep sheltered terrain today, especially on the northern end of the compass where there has not been a sun crust forming on the surface. If you are in complex terrain it is important to make a plan to manage your sluff to avoid being pushed over a cliff or into an area you would rather avoid.

Natural avalanche in Skookum Valley which connected across this entire slope that likely released during or soon after the storm on Tuesday night. Photo Graham Predeger 3.8.24

Weather models have been struggling to accurately predict cloud cover the last few days. We are right on the edge of a low pressure system centered in the Gulf of Alaska, so a small shift in the location of that storm system could bring either full cloud cover or mostly sunny skies. Wet loose avalanches and cornice fall are likely if the sun comes out today. These will be most likely during the afternoon once the sun has had some time to warm up the snow surface. Cooler temperatures and cloud cover today might keep the sun at bay, but if the sun comes out keep an eye out for steep southern slopes and corniced ridges getting direct sunlight.

Wet loose avalanches releasing off rocky outcrops in the afternoon yesterday in Skookum Valley. Photo Graham Predeger 3.8.24