Regions
Northwest Coastal.
New snow with light SW winds will continue to build wind slabs on the lee sides of ridges at treeline and above. Cornices continue to grow, pay special attention to cornices and their run outs.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Saturday
Weather Forecast
The Northwest Coast should see a steady progression of relatively weak frontal systems through the weekend. TODAY: Freezing level around 1200 m, 1 to 5 cm of snow, light to moderate south winds. SATURDAY: Freezing level around 1300 m, possible 2 to 15 cm of snow, winds forecast to be moderate from the southeast. SUNDAY: Freezing level dropping to 600 m overnight, then climbing to 1200 m during the day, possibility of light convective flurries, light winds forecast from the south west. MONDAY: Cloudy with clearing skies, freezing level dropping to 600 m overnight, then beginning a rise to 2000 m by Tuesday. For more detailed mountain weather information visit avalanche.ca/weather
Avalanche Summary
Reports from yesterday tell of moist snow, loose-wet avalanches up to size 1.5 on solar aspects, and in the north of the region, a natural size 2 avalanche was observed on north facing terrain at 2100 m. It is believed to have been the new storm snow running on March 23rd surface hoar. The slab was 25 cm deep and started on a 40 slope.
Snowpack Summary
In the last 48 hours 5 to 10 cm of snow has fallen accompanied by moderate to strong southerly winds. At treeline and in the alpine small wind slabs are expected to have formed. These wind slabs overlie a variety of surfaces which include a hard crust on solar aspects above 1300 m, moist or refrozen snow on all aspects below 1300 m, and settled wind slabs in exposed high elevation terrain. A layer of surface hoar or melt-freeze crust buried on March 3 is down 50-80 cm and has been on the radar of professionals in the mountains north of Stewart. A more widespread crust/facet layer buried in early February can now be found down over a metre. Both of these deeper layers have become less likely to trigger, but have the potential for large avalanches especially with a large trigger such as a cornice fall. I'd be increasingly cautious during periods of warming and intense solar radiation.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
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.