Regions
Northwest Coastal.
Localized solar radiation, snow amounts and wind values may be higher than forecast. Avoid avalanche terrain during periods of heavy loading by snow, rain and wind.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Winter continues in the North as another intense storm moves onto the coast tonight resulting in very strong winds and moderate precipitation amounts. Very unstable air will result in unsettled conditions on Tuesday where localized heavy precipitation is possible (10-30 mm) accompanied by strong west winds and freezing levels near 1000 m. On Wednesday, precipitation amounts could see up to another 25 mm, freezing levels and winds consistent with Tuesday. There will be a lull in the weather pattern Thursday before things redevelop on Friday as another storm tracks across northern BC.
Avalanche Summary
Recent explosive control has produced loose dry avalanches up to size 1.0. With continued snow, rain, and strong winds natural avalanche activity will occur on Tuesday, touchy wind slab and storm slab avalanches size 2 or greater will likely be the primary concern.
Snowpack Summary
At upper elevations 25- 40 cm of recent low density storm snow has been redistributed by strong south west winds into wind slabs on lee slopes. With recent changing winds from the NE, you may find some reverse loaded pockets in unsuspecting places. The lack of bond between the new wind slabs and storm slabs over the older snow surfaces buried on April 9 th (surface hoar, crusts and facets) are the primary concerns. The March 25th surface hoar / crust layer is reportedly unreactive, however; with the new load of wind and snow this should remain on your radar as it may re-awaken, initiating very-large and destructive avalanches.
Problems
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.