Regions
Northwest Coastal.
A Special Public Avalanche Warning continues for this region. Conservative route selection and cautious decision-making is required.
Weather Forecast
Sunday: Mainly cloudy with light snow. The freezing level is around 400 m and winds are moderate from the southeast. Monday: Periods of snow – 10-15 cm. The freezing level rises to 800-1200 m and winds increase to strong from the S-SW. Tuesday: Periods of snow. The freezing level is around 1000-1500 m. Winds remain moderate or strong from the SW.
Avalanche Summary
Observed avalanche activity varies throughout the region. Some reporters observed a fairly widespread avalanche cycle with numerous slabs up to size 2.5, mainly from slopes at and below treeline. Others reported only a couple natural slab avalanches up to size 2 from wind-loaded features. On Friday, there was one report of a size 3.5 slab that was remotely triggered by a helicopter touching down. Variable avalanche activity highlights the current challenges with buried and touchy persistent weaknesses.
Snowpack Summary
Light snowfall and steady moderate S-SE winds continue. Expect fresh wind slabs overlying older wind-affected surfaces in exposed lee and cross-loaded terrain. The January 9th surface hoar/facet layer down 50-70 cm in most places, and seems most concerning at and below treeline. Approximately 10 cm below this weakness you might find the Dec. 26/31 surface hoar layer. Reports of remote triggering, whumpfing, and sudden "pops" shears are all indications that both these layers could propagate well if triggered. Deeper persistent weaknesses buried in December have the potential to wake-up to heavy loading, rapid warming, or avalanches stepping-down.
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.