Use increased caution during afternoon warming, especially on sun exposed slopes.
Confidence
Fair - Timing or intensity of solar radiation is uncertain on Wednesday
Weather Forecast
Synopsis: The South Coast should remain mostly dry under the ridge of high pressure until Thursday evening when a more potent front makes landfall.Wednesday: Freezing Level: 1400m - 1700m; Precipitation: Nil; Wind: Treeline: Light, Variable | Ridgetop: Moderate, NWThursday: Freezing Level: 1100m - 1600m; Precipitation: Trace; Wind: Treeline: Light, S | Ridgetop: Moderate, SWFriday: Freezing Level: 1100 - 1800m; Precipitation: 1:10mm - 1:15cm; Wind: Treeline: Moderate, SW | Ridgetop: Strong W/SW
Avalanche Summary
Warming temps drove a natural avalanche cycle to size 3 on Monday. It's important to note that many of these large avalanches were running on shady N-NE facing slopes between 1900 - 2200m. Several smaller loose snow avalanches to size 2 were running in the recent storm snow on all aspects too.
Snowpack Summary
Daytime high temperatures are hovering near zero as high as 1900m. Moist snow to 1600m was reported on Monday.The weekend storm produced 15 - 70 cm of new snow. A gentle melt/freeze cycle Sunday and Monday is helping this snow to bond to the underlying melt freeze crust that exists below 2100m, on all aspects with the exception being north facing terrain above 1500m where the crust is not present. The first part of the storm was accompanied by strong southerly winds that formed Isolated wind slabs immediately below ridge crest. This snow adds additional load to the mid March surface hoar / crust interface, now down 80 - 110cm. The bond at this interface is improving making it less susceptible to human 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.