Regions
Northwest Coastal.
Strong northeast winds will transport snow and maintain dangerous avalanche conditions.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
The strong outflow (northeasterly) winds will decrease on Wednesday. No precipitation is expected until late Thursday, with below average temperatures until then. WEDNESDAY: Sunny. Winds easing to light northwesterly (10-15 Km/hr). Alpine temperatures around -15 Celcius.THURSDAY: Increasing clouds throughout the day. Moderate to strong (south) westerly winds (35-50Km/hr). Alpine temperatures warming to -12 Celcius.FRIDAY: Snow returns with 15-20cm forecast. Strong (60Km/hr) south winds at ridgetop. Alpine highs to -5 Celcius.
Avalanche Summary
Over the past few days we've had several reports of natural and human-triggered windslabs (mostly Size 2) in all areas of the region, especially on westerly aspects. Reports from social media show touchy windslabs in the Sterling area, southwest aspect.https://www.facebook.com/groups/314113201944133/permalink/1329849827037127/Another natural persistent slab avalanche was reported in the Ningunsaw area last Thursday, indicating that the persistent problem will linger for some time in the northern part of the region.
Snowpack Summary
Recent strong winds (southeast through northeast) have redistributed the 20-40 cm of snow from Friday-Saturday at all elevation bands. This snow sits on a variable interface composed of hard wind slabs, weak surface hoar (Jan 5/6 layer) and faceted snow. The net result is touchy slabs on wind-loaded features and is giving easy to moderate sudden results in snowpack tests. Below the new snow, a well settled slab sits above the Christmas surface hoar layer which is well preserved in southern areas. This surface hoar is now buried 60-100 cm deep, and is still reactive in sheltered areas and steep open features at and below treeline. Deeper weak layers have only been reactive in areas with thin snowpacks. This includes a facet layer from early December that has been reactive in snowpack tests at lower elevations in the southern part of the region, and weak facets near the ground that have produced avalanches in the northern part of the region.
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.
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.