This forecast is based on less than 10cm of new snow Thursday night and Friday. If snow totals unexpectedly reach 15 to 20 cm, the new slab will likely be touchy, and the danger considerable at all elevations.
Confidence
Poor - Timing, track, or intensity of incoming weather system is uncertain on Friday
Weather Forecast
Synopsis: The front and the associated upper trough move through the coast Thursday night. Onshore flows in the wake of the front aren't expected to deliver more than trace amounts Friday. The story is the same though the weekend, small amounts of precipitation accompanied by moderate winds. Looks like potential for a big warm up Monday.Thursday Night: Precipitation: 3:8mm - 4:15cmFriday: Freezing Level: 1000m - 1800m; Precipitation: 1:3mm - 1:5cm; Wind: Treeline: Moderate, SW | Ridgetop: Strong, SWSaturday: Freezing Level: 1200m - 1800m; Precipitation: 1:8mm - 1:10cm; Wind: Treeline: Moderate, SW | Ridgetop: Strong, SWSunday: Freezing Level: 1200m - 1900m; Precipitation: Trace; Wind: Treeline: Light, Variable | Ridgetop: Moderate, NW
Avalanche Summary
Avalanches ran naturally to size 2.5 on north facing features Wednesday. Skiers triggered small wind slab avalanches in steep terrain on alpine features too.Correction, the size 2 reported yesterday from a W/SW facing feature at 2300m was not a natural, it was actually remote triggered by a skier from 10m away.
Snowpack Summary
The snow surface is a mix of surface hoar, small grained facets and melt freeze crusts.Recent warm temperatures have helped to settle and strengthen the upper snowpack. Down 15 - 70 cm below the surface, snowpack tests are still producing hard resistant planar shears on the late March crust.The mid March surface hoar/ crust interface now down 80 - 110cm is decreasing in it's sensitivity to triggering.The early-March crust/facet layer is down about 100-150 cm and the early February layer is now down close to 200 cm. These layers are largely dormant at this time.The lower snowpack is strong and well settled.
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.