Regions
Northwest Coastal.
Weather Forecast
A Pacific frontal system will arrive on the North Coast Tuesday morning and storm conditions should persist through Wednesday. Thursday is expected to be relatively dry.Tuesday: Snow or rain 15-20mm, freezing level 700m overnight, 1200-1400m afternoon, ridgetop winds 60-80 km/h SWTues. Night/Wednesday: Snow or rain 20-30mm, freezing level 1200-1400m overnight, falling to around 1000m in the afternoon, ridgetop winds 60-80 km/h SW, easing in the afternoonThursday: A mix of sun and cloud, dry conditions, freezing level 500m overnight, 800m afternoon, ridgetop winds light S-SW
Avalanche Summary
On Saturday and Sunday, we received reports of many size 2-3 slab avalanches from higher elevations on a variety of aspects. Most of these seemed to release within the recent storm snow or on the previous snow surface buried on March 7. Also reported were numerous natural loose wet avalanches up to size 2 below treeline from warming temperatures and rain.
Snowpack Summary
Around 50-80cm of recent storm snow now sits on previous snow surface which may consist of the following: (1) hard wind slabs or wind-scoured slopes in exposed terrain, (2) a thick layer of faceted snow on sheltered, shady slopes, (3) isolated surface hoar on sheltered, shady slopes, and (4) sun crust on steep solar aspects. Expect moist or wet snow below 1000m, possibly with one or two new crusts near the surface. The mid February weak layer of surface hoar or a crust/facet combo is buried 90-150cm deep. This layer continues to react in snowpack tests, primarily on sheltered north aspects at or below treeline. Basal facets and/or depth hoar remain a concern in shallow snowpack areas in the northern part of the region.
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.