New snow continues to add to the developing storm slab. The next Pacific storm should arrive on Thursday.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Overnight and Wednesday look pretty dry, with light Southwest winds and daytime freezing levels rising up to about 800 metres. The next Pacific system is forecast to hit the coast early Thursday morning and move quickly inland. Expect strong Southwest winds and 5-10 cm of snow during the day and another 5-10 cm by Friday morning. Freezing levels are expected to rise quickly on Friday to at least 1500 metres in the North of the region and up to 2000 metres in the South combined with strong Southwest winds. The storm should continue through Saturday.
Avalanche Summary
Several size 1.0 natural avalanches released in the new storm snow on Monday. On Tuesday there was a size 1.5 skier accidental near Golden with three people involved that may have released on the mid-January persistent weak layer on an East aspect in the alpine.
Snowpack Summary
A thin layer of new storm snow (10-20 cm)has fallen on a variety of old surfaces, including hard crusts, breakable crusts at higher elevations, and surface hoar in some areas. A melt freeze crust can be found up to about 2200m. At higher elevations, the surface is heavily wind affected. The depth of the mid-January surface hoar is highly variable across the region and it may have been destroyed by warmth at low elevations. Where it does exist, it can be found between 30 and 70 cm below the surface. The mid-December surface hoar layer lies below a strong mid-pack down about 60 to 120cm. Both of these persistent layers have been reactive recently. The mid-November weak layer of crusts and facets can still be found near the bottom of the snowpack. It has been unreactive lately, but should be on your radar in shallow snowpack areas where there is more chance of triggering.
Problems
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.
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.