Storm slabs continue to be reactive to human triggers at treeline and above. They may be touchier on leeward slopes due to wind loading and have potential to be remotely triggered from a fair distance away.
Conservative travel habits and patience is key.
30 to 50 cm of recent storm snow has blanketed upper elevations. Storm slabs may continue to be reactive to human triggering on Thursday. The likelihood of triggering a storm slab increases in steep or convex terrain and in wind loaded areas.
Loose wet avalanches are possible from steeper terrain features below treeline. Brief periods of sunshine may easily trigger loose wet avalanches at all elevations especially on south facing slopes.
Change is in the air with an unstable airmass bringing convective, spring-like weather. Generally, overcast skies and a drying trend will exist Thursday. The ridge should be set up by Friday with clearing skies and light northwest winds.
Wednesday Night: 5-10 cm of new snow. Freezing levels dropping to 1000 m overnight and moderate southwesterly wind at ridgetop.
Thursday: Cloudy skies. Convective flurries up to 10 cm with light northwest wind. Freezing levels 1000 to 1500 m.
Friday: Sunny skies with spring-like (diurnal) freezing levels dropping to 1000 m overnight and rising to 1500 m during the day. Ridgetop wind moderate from the northwest.
On Wednesday, a natural avalanche cycle up to size 3 was reported as well as a skier remote (from 40 m away) size 2.5 from on east aspect around 1700 m. This avalanche reportedly failed on the mid-February sun crust/ surface hoar interface down 50 cm with wide propagation. Another skier triggered storm slab size 2 was also reported from a stepper east facing slope.
On Tuesday, a few small size 1 wet loose avalanches were reported at lower elevations.
On Monday, storm slabs were still reactive but less electric than Sunday. A natural cycle up to size 2 was observed through limited visibility in the Whistler backcountry. Explosive control work produced mostly size 1s with a couple size 2 storm slabs. On the other side of the 99, a size 1 wet slab was observed sliding on the crust on an east aspect at 1500 m.
30-50 cm of wind affected, storm snow sits over a variety of surfaces including sun crusts on solar aspects, a thick rain crust in windswept terrain and facets in shady, sheltered terrain. Reports indicate that there is generally a decent bond to the old surfaces below in some areas and a poor bond in others. Large and looming cornices have grown during the recent storm. The upper snowpack is moist or wet below 1400 m.
A crust/facet/surface hoar interface formed late-January is buried down 40-100 cm. This layer was most reactive between 1700 m and 2000 m. While this layer has been dormant in most of the region lately, large loads such as heavy snowfalls and cornice falls could wake it up and produce very large avalanches.
