Regions
Northwest Inland.
Monday's storm could pack a punch and is driving the Danger Ratings.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
Unsettled conditions bringing light precipitation amounts will persist through the weekend. Overnight Sunday an intense, direct frontal system will slam the North Coast bringing moderate precipitation amounts and rising freezing levels to Inland Regions.Sunday: Freezing levels rising to 1200 m and expecting 10 mm. Ridgetop winds strong from the south. Monday: Freezing levels rising to 1800 m and expecting up to 20 mm. Ridgetop winds strong from the south gusting to extreme values. Tuesday: Freezing levels falling to 1100 m or lower. Precipitation amounts 10 mm. Ridgetop winds moderate from the south.
Avalanche Summary
No recent avalanche activity has been reported. Last Tuesday a steep rocky NE facing feature at 1900m released naturally resulting in a size 3 avalanche. The possibility for large avalanches appears to be still there, and the chance of one is likely to increase with anticipated warming, and/ or localized new loads including precipitation and strong winds on Monday.
Snowpack Summary
Up to 20 cm new snow recently fell onto a variety of old snow surfaces consisting of surface hoar, small grained facets and melt freeze crusts. A poor bond likely exists.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 possibly 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. While it's been mostly dormant, I would not rule out the possibility of it reawakening if we see prolonged warming and/or intense sunshine.
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.