Regions
Northwest Coastal.
A strong storm should reach the northwest tonight. Some areas could see as much as 80 cm by Thursday night with strong to extreme winds. Probably worth waiting this one out!
Confidence
Fair - Track of incoming weather is uncertain
Weather Forecast
Synopsis: A strong frontal system pushing into the Northwest by Thursday. Precipitation amounts look heaviest close to the coast (Stewart, Bear Pass) but areas near Terrace should see at least moderate amounts. Overnight and Thursday: Moderate to heavy snow – 25-60 cm. The freezing level is around 800 m. Winds are very strong from the west-southwest. Friday: Cloudy with possible sunny breaks. The freezing level lowers to 500 m. Winds ease to moderate from the northwest. Saturday: Light snowfall. The freezing level is near valley bottom. Winds pick up again from the northwest.
Avalanche Summary
Recent reports include numerous natural moist slab avalanches up to Size 2.5 and widespread wet sluffing with warm temperatures and light rain on Monday. In the eastern part of the region, extreme winds caused numerous thin wind slab avalanches in alpine areas below ridgetops, and strong solar radiation caused a few Size 2 released right to the ground. On Sunday there was a report of a size 1.5 skier triggered avalanche on a steep unsupported convex roll on a northerly aspect. This event likely released on the late December surface hoar layer approximately 60 cm deep. There are also a few reports of glide releases in steep south facing terrain.
Snowpack Summary
Mild temperatures have resulted in moist snow below treeline, while strong or extreme upper winds have scoured areas and produced hard or soft wind slabs in a variety of areas at all elevations. Below this, weaknesses within the 30-60cm of well settled storm snow are only producing resistant fractures in recent snowpack tests. However, a persistent weakness of surface hoar or facetted snow buried at the end of December sits at the base of this recent storm snow and continues to react as sudden fractures in snowpack tests particularly below treeline. The mid and lower snowpack is generally well settled and strong, although well developed basal facets remain a concern in shallow snowpack areas.
Problems
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.
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.