Minor weather inputs Friday were enough to overload our frail and fragile snowpack. With heavy snowfall, strong winds and rapid warming in the forecast, Saturday will be a good day to stick to conservative terrain, and minimize overhead hazard.
There are three persistent weak layers buried in the mid-upper snowpack. All three of these layers are still reacting in the easy/moderate range in snowpack tests around treeline. As the new snow continues to pile up, and the resulting avalanches increase in size, the likelyhood that they will step down to these older layers will increase.
The new snow is not bonding well to the old facetted surfaces, expect loose snow avalanches in confined, steep and sheltered terrain.
Storm slabs will build rapidly on Saturday. Heavy snowfall, wind and warming temps will load up the start zones quickly, triggering natural avalanches.
An avalanche cycle has begun, with numerous loose dry and thin storm slab avalanches observed in the highway corridor on Friday. These were mostly in the size 1.5-2.5 range, with one notable size 3.0 out of the Lens path on the south side of Mt. Tupper.
A field team in the Fidelity area on Friday was easily able to trigger a size 1.5 very thin slab avalanche, in a steep north facing couloir at Treeline.
Large settlements and whumphing have been reported recently, in previously untracked terrain.
Ongoing snowfall is covering a generally weak and facetted snowpack. Storm snow accumulations should reach ~15cm by Saturday morning, with an additional 20-25cm forecast to fall through out the day
The alpine snowpack is particularly thin and variable for this time of year, with shallow areas facetted and unconsolidated from the snow surface to the ground.
There are several persistent weak layers buried, which are most prevalent at and near treeline. The Dec 16 interface is down ~20cm, and consists of surface hoar (up to 10mm) and a crust on solar aspects. The Dec 5 surface hoar layer is down ~40cm. The Nov. 17th surface hoar/suncrust layer is down ~80cm and is the suspected failure plane for recent whumphing locally, and some large avalanches in neighboring areas.
A moist pacific system continues to drive weather inland from the Coast.
Up to 35cm will fall Friday night through Saturday evening, with the heaviest snowfall happening midday. Ridgetop winds will increase to strong from the SW, and alpine high temps will be -4°C.
Sunday will be a break between fronts. Scattered flurries will give up to 4cm, the alpine high will reach -2*C with a 1600m freezing level , and ridge wind will be light gusting moderate from the SW.
Monday will bring another wave of heavy snow.
