Regions
Northwest Coastal.
Rising freezing levels will keep the avalanche danger high and will bring rain to the alpine in the south of the region.
Confidence
Fair - Freezing levels are uncertain
Weather Forecast
Synopsis: The next frontal wave with push onto the north coast early Thursday morning causing temperatures to spike before it shift southwards. Expect heavy precipitation to continue.Tonight and Thursday. Snow amounts: up to 20 cm overnight becoming heavy rain Thursday in the south, snow further north / Freezing levels: Rising to 2500m in the south, 1300m in the north / Ridge winds: Strong westerly. Friday: Snow amounts: Up to 10 cm / Ridge winds: Strong westerly / Freezing levels: 800m.Saturday: Snow amounts 10 to 20 / Ridge winds Light westerly / Freezing levels: 800m.
Avalanche Summary
No new observations. Numerous large- very large 2-3 natural slab avalanches occurred during the last storm and observed recently. Most seemed to be storm slabs and wet slabs, and glide crack releases.
Snowpack Summary
Freezing levels are going to be the thing to watch on Thursday.In the south were freezing levels are expected to climb as high as 2500m, rain will deliver a significant load to an already suspect upper snowpack. Further north continuing heavy snowfall and warming temperature will likely form widespread and reactive storm slabs.The December 22nd surface hoar is currently down 100cm in areas that did not avalanche during the last storm cycle.The mid pack features several persistent weak layers but these have likely gained strength at this point.In the north of the region a basal facet and crust combo lingers near the ground. It is most prevalent on NW - E facing aspects at the upper TL and alpine elevations.
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.