North Columbia

Prolonged reactivity of storm slabs has earned them a persistent slab label, but the avoidance strategy hasn't changed. Keep it in mind as you navigate around the more obvious wind effect.

Moderate -

Tuesday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1100 metres with alpine high temperatures around -8.Wednesday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds. Freezing level to 1000 metres with alpine high temperatures around -9.Thursday: Cloudy with flurries bringing about 5 cm of new snow, continuing overnight. Light east winds. Freezing level to 900 metres with alpine high temperatures around -10.

Reports from Sunday included several more storm slab and wind slab avalanches from size 1-2. These were both skier-triggered and ski cut on north to east aspects at around 2000 metres and above. Shallower slab depths have begun to highlight the mid-storm interface indicated in our snowpack discussion, but at least one larger storm slab failed at the deeper late-March layer, now labeled a 'persistent slab'.Saturday's reports included numerous observations of storm slabs releasing naturally as well as with remote (from a distance) triggering, skier traffic and explosives control. Sizes ranged from 2-3, with crown fracture depths varying from 30-100 cm. This activity occurred on all aspects but was focused at alpine elevations.Friday's storm caused another natural avalanche cycle with numerous size 1-2 avalanches in the top 20-30 cm of new snow.Storm slab avalanches have been reported on a regular basis since Tuesday's storm, with natural avalanches up to size 3 initially reported on all aspects from 1900-2800 m. South and west aspects have been most reactive with slabs running on the recently buried late-March crust.

A variable 5-20 cm of new snow over Sunday night has brought storm snow totals from the past week to a wide-ranging 40-90 cm. The snowfall was initially accompanied by strong west wind and formed reactive slabs at higher elevations. More recent north winds reached extreme, so a mix of stubborn old and newer, more reactive wind slabs can now likely be found on a range of aspects. Below the wind effect at the surface, a break between storm pulses allowed for the formation of yet another layer of sun crust (south aspects) and surface hoar (shaded aspects) that is now buried by 20-30 cm of new snow. The full depth of recent storm snow sits on a persistent weak layer buried in late-March that consist of crusts below 1900 m and on south aspects, and surface hoar on shaded aspects at higher elevations.A deeper layer buried mid-March is now 60 to 90 cm below the surface, and is similar to the late-March interface.Deeper persistent weak layers from January and December are still being reported by professional observers, but are generally considered dormant.