Touchy and dangerous conditions still exist in many parts of the region. With a warm, wet and windy storm on the way, conditions will continue to deteriorate.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Wednesday
Weather Forecast
Warm, wet and windy conditions will persist for most of the forecast period. Expect up to 15mm of precipitation on Wednesday with another 20mm possible Wednesday night. Winds on Wednesday will be extreme from the southwest while freezing levels will hover around 2300m. On Thursday, the region should see between 10-20cm of snow, strong southwest winds and freezing levels dropping from 1800 to about 1400m. On Friday continued snowfall is expected with accumulations ranging from 5-15cm. Winds should taper-off dramatically with freezing levels dropping to about 1000m.
Avalanche Summary
A widespread avalanche cycle to size 3 was observed last weekend in response to heavy snowfall, wind and warm temperatures. Many of these avalanches were persistent slab avalanches which failed on recently buried surface hoar. More recently, a skier-triggered size 2 persistent slab avalanche was observed in the north of the region around Birkenhead Lake. Check out the great Mountain Information Network posts that detail the touchy conditions in this area. Looking forward, continued warm, wet and windy weather is expected to spark ongoing wind slab activity in high elevation lee terrain, but warm temperatures and loading will also increase the likelihood of waking up any lingering persistent weaknesses that were not triggered by last week's storm.
Snowpack Summary
On Wednesday, moderate snowfall and strong winds will continue to form deep and dense storm slabs in high elevation terrain and cause substantial cornice growth. At treeline and below, rain is forecast to further saturate the upper snowpack. Heavy loading from last week's storm and the resulting avalanche cycle, has helped flush-out the mid and early-January surface hoar/facet layers now down 60-120 cm deep. However, these layers are still intact and reactive in many places and it may still be possible to trigger large slabs. The mid and lower snowpack is generally strong, with the exception of shallower snowpack areas that may be more faceted.
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.
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.