Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain on Thursday
Weather Forecast
Synopsis: A pacific frontal system passes over the region Thursday night bringing light to moderate precipitation. A modified arctic front pushes south over the region Saturday followed by a cool upper trough which should result in spotty snow showers and cooler temps. A strong upper ridge moves inland Sunday resulting in mainly sunny skies and rising freezing level. Thursday Night: Freezing Level: 1600m; Precipitation: 2:10mm - 2:15cm; Wind: Treeline: Moderate SW | Ridgetop: Strong to Extreme W/SWFriday: Freezing Level: 1500m rising to 1700m; Precipitation: 2:4mm - 2:8cm; Wind: Treeline: Moderate+, W | Ridgetop: Strong, WSaturday: Freezing Level: Valley Bottom rising to 1500m; Precipitation: Trace; Wind: Treeline: Light, N | Ridgetop: Light, NSunday: Freezing Level: Valley Bottom rising to 2000m; Precipitation: Nil; Wind: Treeline: Light, SW | Ridgetop: Light, NW
Avalanche Summary
On Wednesday natural avalanches ran to size 2.5 on north and east facing features around 2500m. One of these events was initiated by cornice fall.In two separate incidents Tuesday, natural cornice fall on 38 - 40 (degree), NE facing features around 2400m, initiated size 3 avalanches that failed on the mid-February crust/facet/surface hoar combo with crowns up to 120cm in depth. A natural avalanche with a 45cm crown on a NE facing feature at 2500m was also reported.
Snowpack Summary
15 - 20 cm of new snow fell on Tuesday night.Warm temperatures resulted in the freezing level rising to almost 2000m Sunday/Monday. This has helped to settle out last weeks storm snow at and below treeline, but winter conditions prevail at upper elevations. Strong winds out of both the SW and NW have recently distributed dry snow in the alpine into wind slabs that remain sensitive to human triggering.Three persistent weak layers exist in the highly variable snowpack of the Cariboos:The mid-March sun crust/surface hoar layer down 50-80cm still has potential for human-triggering in isolated areas. The early-March crust/facet/surface hoar layer down around 80-120cm has become less susceptible to human triggering, but still has the capacity to produce large avalanches.The mid-February crust/facet/surface hoar combo is typically down 150 - 200cm. Direct triggering of this layer has become unlikely, however, cornice fall, a smaller avalanche in motion or prolonged warming may wake this layer up, which would result in very large and destructive avalanches.
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.