Regions
Northwest Coastal.
Monday's storm will pack a punch and is driving the Danger Ratings. The snowpack does not typically handle rapid change well and deeply buried persistent weak layers may re-awaken.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
Unsettled conditions bringing light to moderate precipitation amounts will persist through the weekend. On Sunday night an intense, direct frontal system will slam the North bringing heavy precipitation and rising freezing levels. Sunday: Freezing levels rising to 1000 m and expecting 10-20 mm. Ridgetop winds generally light from the south with strong gusts. Monday: Freezing levels rising to 1400 m and expecting up to 50 mm in coastal areas (Kasiks) and up to 30 mm inland (Bear Pass, Stewart, etc.). Ridgetop winds strong from the south gusting to extreme values. Tuesday: Freezing levels falling to 1000 m or lower. Precipitation amounts 10-20 mm in coastal areas with lower amounts near 10 mm as you move inland.
Avalanche Summary
The recent storm snow has shown a fairly poor bond to the older snow surfaces. Natural loose dry and wet avalanche activity up to size 2 was reported on Friday. Continued natural avalanche activity is expected at all elevations through the forecast period.
Snowpack Summary
Up to 30 cm new snow fell onto a mix of surface hoar, small grained facets, melt freeze crusts and firm wind pressed snow. The new snow seems to be bonding poorly to these older snow surfaces and isolated wind slabs have formed at upper elevations.Previous snow that fell between March 27-30th fell on top of a variety of old snow surfaces. I suspect the ongoing melt freeze cycles have largely healed any instabilities associated with this interface. Below treeline a spring-like snowpack exists including melt-freeze crusts and isothermal conditions. Two persistent weak interfaces exist deeper in the snowpack. The early March layer can be found down 75 - 100cm and is composed of facets/surface hoar on shady aspects and facets/crust on southerly aspects. The early February crust/facet/surface hoar combo is down 150 - 200cm. This layer was responsible for a couple of unexpected large avalanches right at the end of March and the beginning of April. These layers should be on your radar and could become reactive with intense loading from rain/snow, warm temperatures and strong winds that are expected during this forecast period.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.