Watch for fresh and reactive storm slabs forming Thursday as new snow arrives amid strong wind. Keep in mind the potential for triggering deeper slabs may persist even as natural activity from the previous storm tapers off.
40-80 cm of recent storm snow sits overtop a thick layer of weak, sugary facets. In the Monashees, this interface appears to be bonding well, while reactivity may persist longer in the Selkirks.
10-20 cm of new snow falls amid strong wind. Storm slabs will be most reactive where they sit over a sun crust and in wind deposited pockets in lee terrain features at upper elevations.
Cornices are experiencing rapid growth with strong west to southwest winds. Fresh, unsupported tabs that break off can act as triggers on slopes below.
WEDNESDAY NIGHT: Increasing cloud with flurries bringing up to 5 cm, light wind increasing to strong southwest, freezing level valley bottom.
THURSDAY: 5-10 cm of new snow, strong southwest wind easing to moderate, freezing level 1200 m.
FRIDAY: 5-15 cm of new snow, light to moderate northwest wind, freezing level 1000 m.
SATURDAY: A trace of new snow, light to moderate southwest wind, freezing level 1000 m.
During the storm last weekend and into Monday, the northern Selkirks were host to a cycle of very large natural and explosive triggered avalanches size 2-4, while the Monashees had surprisingly limited activity up to size 2. The storm was late to the southern half of the region which was quiet until reports from Monday described natural, explosive and skier triggered avalanches size 1-2, as well as one report of a natural cornice triggered size 3.
Post-storm in the Monashees, slabs quickly became stubborn to trigger, as described in these MIN reports from Monday here and here. On Tuesday in the Selkirks near Revelstoke, a skier remote size 2 was reported while explosive work just south of town produced limited results including a few size 2 storm slabs on S-SE aspects in the alpine.
We have had few reports from the south of the region of the odd persistent slab avalanche running on the late January interface. These have been around size 2, skier triggered out of steep, cliffy, unsupported terrain around treeline. At least one occasion was in a location where an avalanche had previously slid and the bed surface reloaded.
10-20 cm of new snow is forecast to fall by the end of the day Thursday. It falls over 40-80 cm of recent storm snow which is well settled at lower elevations and heavily wind affected at upper elevations. Wind deposits up to 100 cm deep can be found in lee terrain features in the alpine and may remain reactive to human and machine triggers.
All of this recent snow sits over facetted surfaces from the mid February cold snap. There is uncertainty around how long it will take for this interface to bond but reports from the Monashees have indicated a positive trend already.
We've now got 70 to 120 cm of snow above the late January persistent weak layer which is composed of surface hoar in openings in the trees and/ or a crust on steep solar aspects. Very isolated activity on this layer has been observed recently, usually skier triggered in steep, cliffy, unsupported terrain around treeline in the south of the region.
