Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain on Sunday
Weather Forecast
The next couple days brings cooler temperatures and dryer conditions. Friday: Mix of sun and cloud in the afternoon. Light snow amounts near 5cms. Ridgetop winds 20-30km/hr from the SW. Alpine temperatures near -9. Freezing levels at valley bottom. Saturday: A Northerly flow brings mainly sunny skies with seasonal conditions. Ridgetop winds 15-20km/hr from the NW. Treeline temperatures near -9. Sunday: Light to moderate precipitation is expected accompanied by strong SW winds. Freezing levels may rise to 1300m in the Northern part of the region, and 2000m in Southern locations by the afternoon.
Avalanche Summary
One large natural slab avalanche was reported. This was a size 2.5 that occurred on a East aspect, at 2500m. The crown was 100cms in depth, 100m wide, and ran 200m down slope. Natural activity has tapered off, I'd still be suspicious of the mid-December layer susceptible to rider triggers (especially sledders) creating large avalanches. Please don't rule this out yet.
Snowpack Summary
Some locations in the region has received up to 50cms in the past 48hrs. In the alpine and at treeline this new snow is being blown onto lee slopes and terrain features adding to previous soft slabs and wind slabs. In sheltered locations this new snow buries the surface hoar that formed over the New Years. We'll date this the January 3 SH layer, the crystals reported to be up to 10mm. This may become a concern with increased load as it reaches it's threshold. Some locations in the region received some rain up to 2000m, but consistent rain to 1500m. This may have solved our lower elevation New Years surface hoar layer. Below the surface down 80-140cms lurks the mid-December surface hoar/ crust/ facet layer. This is a layer of concern. Test results on this are still variable in the moderate to hard ranges with sudden planar characteristics. It continues to be sensitive to large triggers like cornice fall and explosives. Between this layer and the bottom of the snowpack sits a well settled mid pack. At the bottom of the snowpack basal facets and depth hoar crystals live. These become a concern in thinner snowpack areas, and became reactive under the new load of the post-Christmas storms.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
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.