Avalanche Advisory for 2015-12-21 07:07:34

Numerous observations were submitted from local skiers and have been made by Jon and I over the weekend. Overall, all observations have indicated a strengthening snowpack for both the persistent weak layer problem and wind slabs. Fabulous skiing was had by many as 11-12% powder, right side up, layered the mountain. The backcountry has been world class. The Mt Shasta Ski Park is also in full operation and skiers and riders grinning like kids on Christmas. 

We've been monitoring the persistent weak layer problem closely, hunting to find new areas where the layer might exist and continuing to dig pit's and conduct stability test in areas we know the layer exists. The PWL has not been observed on any new aspects or elevations, however it still exists in areas where already observed from December 13th. Stability tests have trended toward stronger results, but I am still not convinced we should forget about it. The PWL, still just below the thin crust now deeper in the snowpack (70-90 cm snow over PWL), hosted rounded facets on 12/19 and fully propagated under hard hits from the shoulder (ECTP20-30). That said, uncertainty is still high concerning this layer and its future productivity for an avalanche in these isolated areas.. A few thoughts... 1 - The layer still exists in isolated areas just below treeline on W-SW-S-SE aspects.  2 - How much weight from either multiple people on a slope, or snowmobiler, would it take to trigger the PWL?  3 - If triggered, the snow above the PWL is only getting deeper and consequences getting bigger. So, the bottom line: Human triggered avalanches on this layer are unlikely today. BUT, in the locations where this weak layer is found, snowpit tests still indicate the right set of ingredients are in place for an avalanche to occur... read: slab over weak layer. Avoid multiple people on open slopes and consider the weight of your snowmobile (400+ lbs) when high marking in suspect areas. Further, heavy precipitation over the next 48 hours will deposit 1-2 feet of new snow adding more stress to the snowpack. Snow does not like rapid change!

Wind slabs have shown good stability in the past few days. Ridge tops remain scoured and firm. Small cornices have been easy to trigger but not of major concern nor have they triggered further slab avalanches. Easterly aspects have shown the best wind loading. The up and coming storm will deposit heavy snowfall and bring very strong westerly winds over the next 48 hours. Wind slabs are guaranteed and near and above treeline travel will call for careful route planning, if you can even see at all, let alone stand upright.

Below: Full pit profile from Ash Creek Butte area

Skier: C Merrill Photo: N Meyers Location: Gray Butte

Skier: C Merrill Photo: N Meyers Location: Gray Butte

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The Sand Flat cross country ski trails are snow covered and ready for your cross country skis or snow shoes. These are backcountry trails marked with blue diamonds on trees. Trails are not groomed.  Snow shoers, please blaze a parallel trail to cross country skiers staying out of the skin track. Thank you, and Enjoy!

The Pilgrim Creek Snowmobile Park is open! Trails are being groomed currently. Head to our "Education" tab on our website and find the snowmobile section for trail information, grooming status and other sledder resources!

The Five Red Flags of Avalanche Danger any time of year include:  1) Recent/current avalanche activity  2) Whumpfing sounds or shooting cracks  3) Recent/current heavy snowfall  4) Strong winds transporting snow  5) Rapid warming or rain on snow.