Major warming and sun are expected to destabilize the snowpack over the weekend. Wind slabs are expected to remain reactive, cornices will continue to weaken, and deep weak layers may begin to wake up. Wet loose activity should be expected on steep sun exposed slopes.
Wind slabs are expected to remain reactive on Saturday, especially where they overlie a crust. Cornices will also continue to weaken with warming through the weekend.
Wet loose avalanches will become possible at all elevations with warming this weekend. Extra caution will be required around steep south facing slopes when the sun is strong.
An old persistent weak layer buried deeply in the snowpack has been dormant recently but will get tested this weekend with the sustained warming event. Cornice falls or smaller avalanches have the highest potential to step down to a deeply buried weak layer.
The region now sits under the warm ridge of high pressure which is expected to persist into early next week bringing very high freezing levels and sun.
Friday Night: Mainly clear, light NW wind, freezing levels 3000 m with an inversion.
Saturday: Mainly sunny, light NW wind, freezing levels around 3200 m with an inversion.
Sunday: A mix of sun and cloud, moderate W wind, freezing levels around 3000 m with an inversion, dropping to around 2000 m by Sunday night.
Monday: Mainly sunny, light NW wind, freezing levels around 2000 m with an inversion.
On Thursday, natural size 1 sluffing was observed in the north of the region. On Wednesday, a size 1.5 glide slab was observed at 1400 m in the Coquihalla area as well as several size 1 loose wet avalanches sliding on the crust. In the north of the region, a natural size 1 cornice failure was observed on a NE aspect at 2100 m which did not trigger a slab on the slope below.
Parts of the region are currently under a Special Public Avalanche Warning (SPAW). Check out this new blog post for additional information.
At higher elevations, 15-30 cm of recent storm snow has buried the widespread January 16 melt-freeze crust which extends into alpine elevations. There have also been reports of a layer of small surface hoar above this crust in the north of the region on polar aspects at treeline and in the alpine but this does not seem to be widespread. The most recent storm snow has formed reactive wind slabs in exposed high elevation terrain, mainly on north and east aspects. At lower elevations, the upper snowpack is moist or wet from the recent rain event.
The early December crust/facet layer is now typically down 100-150 cm but may be as shallow as 60 cm and as deep as 200 cm with lots of variability through the region. The layer is most prominent between 1700 and 2100 m. The crust appears to be breaking down in the south of the region but remains a concern in the north. The layer has been dormant recently but is a concern for the period of major warming and sun forecast over the weekend. The most likely place to trigger it would be in thin, rocky snowpack areas where it is shallowest.
