Difficult and dangerous conditions exist in the backcountry at this time. Choose cautious and conservative routes.
Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period
Weather Forecast
Synopsis: Starting Thursday night, a Pineapple Express with a narrow moisture stream has the potential to bring moisture to part or all of this region through the forecast period. Due to the narrow moisture stream, there is poor confidence in snowfall amounts at this time.Thursday: Mostly dry during the day. Freezing level around 1100 m. Winds southwest, mostly light, increasing to strong in the afternoon.Thursday night. 10-15 cm new snow, with the possibility of local enhancement. Very strong SW winds.Friday: Moderate snow/rain (around 10 cm/mm, but heavier amounts possible). Freezing level around 1700 m. Southwesterly ridgetop winds to 80 km/h.Saturday: Moderate snow/rain (around 10 cm/mm). Freezing level around 1600 m. Southerly winds around 30 km/h.
Avalanche Summary
On Tuesday, a very large slab avalanche (size 3.5) was triggered by a cornice collapse on a northeast aspect, with a run distance of 800 m. There were reports of additional natural avalanches up to size 3 (on NE and S aspects) as well as explosive control results up to size 2.5. I suspect the majority of the activity is running on a layer of buried surface hoar from February 12th.
Snowpack Summary
40-70 cm of new snow has fallen in the past few days. Strong west-southwest winds have redistributed the new snow into deep wind slabs on exposed lee slopes and cross-loaded gully features. The February 12 persistent weak layer (crust, and/or surface hoar) is now down 60-80 cm and is primed for triggering. Recent snowpack tests have shown easy to moderate "pops" results on this interface and has been particularly touchy on south aspects where a sun crust exists. Deeper persistent weak layers from early February and late January continue to show planar failures when moderate to hard forces are applied in snow pack tests. These deeper layers have not been reactive to the weight of a rider, but they may be triggered by large loads like an avalanche in motion (step-down avalanche), or a cornice fall.
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.