Avalanche danger will be increasing over the next 48hrs with the incoming storm, warm temp's, and strong winds. Conservative route selection is critical right now. Weak layers in the upper snowpack will be tested by the next storm!
Weather Forecast
A trace of snow today with moderate SW winds and a freezing level around 1200m. Thursday brings 25-30cm, strong SW winds, and freezing levels rising to 1500m. Friday will bring in calmer weather, with freezing levels dropping to valley bottom and isolated flurries.
Snowpack Summary
25cm in past 36hrs, warm temp's, and moderate winds are building reactive storm slabs. The Dec 9 surface hoar/facet/crust persistent weak layer is buried 80cm+ and is producing large whumphs and sudden planar results. The Nov 21 surface hoar/facet persistent weak layer is down ~120cm.
Avalanche Summary
10 avalanches to sz 3 were observed in the highway corridor east of Rogers Pass yesterday. Ski tourers at McGill shoulder were able to ski cut surface slabs to sz 1, 15-25cm deep, 10-15m wide along the ridge crest. These slabs were in wind-effected terrain and stopped moving once the slope angle mellowed to <25*.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.