Regions
Northwest Inland.
The incoming storm will load a weak snowpack and create very dangerous avalanche conditions.
Weather Forecast
FRIDAY NIGHT: 5-15 cm of new snow, strong southwest winds, alpine temperatures rising to -5 C.SATURDAY: Another 10-25 cm of new snow with greater accumulations in the north, strong to extreme southwest winds at ridgetop, alpine temperatures around -3 C.SUNDAY: A break in the storm with flurries, sustained strong southwest winds, freezing level around 1000 m.MONDAY: Stormy with 15-25 cm of new snow, extreme southwest winds at ridgetop, freezing level around 1200 m.
Avalanche Summary
Deep persistent slab avalanches continue to be reported in the Ningunsaw area, including natural and explosive triggered size 2.5 avalanche running on basal facets on southwest aspects. A natural size 2 wind slab avalanche was reported in the southern part of the region on Thursday, releasing on a wind-loaded northeast alpine slope.With the incoming storm expect an increase in avalanche activity, including very touchy storm slabs that have the potential to trigger large deep persistent slab avalanches.
Snowpack Summary
On Saturday, expect 15-40 cm of new snow, which combined with warming temperatures and strong winds will form a widespread storm slab problem. Storm slabs will be extra thick and touchy on wind-loaded features. The new snow is burying a layer of feathery surface hoar crystals, which will allow for wide propagations in the storm snow. Snow depth at treeline varies from about 1 m in most areas to 2 m in deeper snowpack areas in the south and west of the region. The shallow snowpack areas mostly consist of weak faceted or sugary grains beneath hard slabs. With the additional load of the new snow these hard slabs may produce surprisingly long fractures resulting in large avalanches, and in some instances they may step down to weak faceted snow crystals near or at the ground.
Problems
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.
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.