Confidence
Fair - Intensity of incoming weather is uncertain on Friday
Weather Forecast
A ridge of high pressure builds off the coast bringing mainly dry, cool conditions with possible scattered flurries on Thursday. Ridgetop winds will blow 30km/her from the NW. Freezing levels may rise to 1200m. On Friday a low pressure system arrives off the coast bringing moderate-heavy precipitation amounts. Snow amounts near 15-25cm. Freezing levels fall to valley bottom. Ridgetop winds strong from the WNW. Saturday snow amounts become light, and taper off by noon. Winds 10-20 from the NW.
Avalanche Summary
Skier triggered (controlled) produced slab avalanches up to size 1.5. on NW-NE aspects. Northerly aspects continue to load with moderate-strong West winds. Explosive control produced avalanches up to size 1.5 on NW-NE aspects @1800-2200m, slab depths 10-40cm. I suspect there will be an increase in avalanche activity with the forecast wind and snow.
Snowpack Summary
New snow over the past few days have buried a variety of old snow surfaces. These old surfaces are now 30-45cm down and include crusts that exist on all aspects at lower elevations and on steep solar aspects higher up. Facets (sugary snow crystals) and spotty surface hoar (feathery snow crystals) may also exist in combination with crusts, so there may be continued slab reactivity at lower elevations. With more snow and wind in the forecast the new load may have a poor bond to the underlying buried surfaces. Keep an eye on solar aspects Thursday afternoon. Wet, moist snow is a sign of instability. The mid and lower snowpack are strong and well settled. The average treeline snowpack depth is about 240cm.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
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.