Regions
Northwest Coastal.
The snowpack needs time to adjust to the shock of a big, long awaited storm. With surface hoar and sugary facets below the new snow it may take longer than usual to stabilize.
Weather Forecast
MONDAY NIGHT: Clearing off and drying out with only flurries. Light to moderate west wind.TUESDAY: Cloudy with sunny periods. Treeline temperatures -5 to -10 C. Light southwest winds.WEDNESDAY: Mix of sun and cloud. Dry. Treeline temperatures around -8 C. Light south wind.THURSDAY: 5 to 10 cm new snow. Moderate south wind. Treeline temperatues -5 to -10 C.
Avalanche Summary
Initial reports from the field today (Monday) suggest whumpfing, cracking, remotely triggered avalanches, and a widespread avalanche cycle on Monday morning.
Snowpack Summary
Widespread and reactive storm slabs and wind slabs. The 40 to 60 cm of storm snow covers a wide variety of surfaces but the key idea is they're all crappy. Avalanche forecasting rule of thumb: the longer snow is exposed on the surface the less likely it is to bond when covered. We've just covered surface hoar, sun crusts, and a widespread weak faceted (sugary) upper snowpack. Early reports suggest the old surfaces, as old as the Feb 19 surface hoar facets is the critical weak interface so avalanches are running deeper / bigger than might be expected. The upper- and mid-pack weakened with the extended cold drought so there are widespread areas with soft faceted snow, and possibly surface hoar. This sugary soft snow has been reactive in some snowpack tests and there have been some small slab avalanches noted on this layer.The lower snowpack is generally considered strong.
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.