Regions
Northwest Coastal.
Forecast precipitation amounts are uncertain. If actual snowfall amounts Monday night through Tuesday are equal to or exceed the upper end of estimates, the avalanche danger will be HIGH.
Confidence
Low - Forecast snowfall amounts are uncertain on Tuesday
Weather Forecast
TUESDAY: Periods of snow, accumulation 5-10cm Monday night and 10-20cm Tuesday / Moderate to strong southwest wind / Alpine temperature -3 WEDNESDAY: Flurries, accumulations 5-10cm / Light to moderate southwest wind / Alpine temperature -5 THURSDAY: Flurries, accumulations 5-10cm / Light to moderate northwest wind / Alpine temperature -4
Avalanche Summary
On Monday avalanche activity was reported as natural and skier triggered windslab activity on east and north aspects at 1300m. Additionally loose dry avalanches to size 1.5 were reported from steep rocky terrain. On Saturday a size 2 remotely (from a distance) triggered persistent slab avalanche was reported to have run on a northeast aspect in the alpine on buried layer of surface hoar.
Snowpack Summary
60-80cm of snow covers a widespread crust as well as surface hoar in isolated areas at mid elevations that were buried mid-January. Surface hoar is more likely to exist in sheltered areas at treeline and below with crust elsewhere. This weak layer has produced easy, sudden results in snowpack tests late last week in the Shames area and also recent avalanche activity at upper treeline and alpine elevations.Professionals have also been monitoring a few mid-pack layers within the snowpack including a crust/ surface hoar layer that was buried early-January and now lies 70-120 cm below the surface, and a similar layer buried mid-December that now lies 100-140 cm below the surface. Both of these layers have been reactive in recent snowpack tests producing moderate to hard, sudden results and have also produced recent large, natural avalanches in northern parts of the region near Bear Pass.The lower snowpack is generally strong, with the exception of areas around Stewart and further north where a basal crust and facets exist.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.