Regions
Northwest Coastal.
Monday could be the calm before the storm(s). Regardless, it is still a day to exercise constraint and conservative decision-making.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Monday: Mainly cloudy with light snow – 2-5 cm. The freezing level is around 1000-1400 m. Winds are moderate or strong from the S-SW. Tuesday: Periods of snow or rain – 10-20 mm/cm. The freezing level climbs to 1200-1500 m and winds remain strong. Wednesday: More rain or snow – possibly very heavy. The freezing level could jump to 2000 m and winds will keep blasting from the South.
Avalanche Summary
Explosives control on Saturday produced numerous slab avalanches up to size 3. Most of these failed on the mid-January surface hoar and some stepped down to the Boxing Day surface hoar layer. One observer also viewed numerous size 3 natural slabs on a variety of aspects, but these may have been a day or two old.
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 60-80 cm in most places, and seems most concerning at and below treeline. Recent snowpack tests give moderate "pops" results on this layer. Approximately 10 cm below this weakness you might find the Dec. 26/31 surface hoar layer. Reports of remote triggering, whumpfing, and sudden shears in snowpack tests 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.
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.