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 may remain reactive on Sunday, especially on shady aspects and where they overlie a crust. Cornices will also continue to weaken with warming through the weekend.
Wet loose avalanches will become increasingly likely with warm temperatures 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 next week bringing very high freezing levels and sun.
Saturday night: Partly cloudy, light to moderate W wind, freezing levels around 3000 m with an inversion.
Sunday: A mix of sun and cloud, moderate W wind, freezing levels around 2700 m with an inversion, dropping to around 2200 m by Sunday night.
Monday: Sunny, light NW wind, freezing levels around 2000 m with an inversion.
Tuesday: Sunny, moderate W wind, freezing levels around 2700 m with an inversion.
On Friday, evidence of natural wind slabs size 2-2.5 were observed in the south of the region, suspected to have run one or more days prior. 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.
Last week, a very large natural avalanche cycle took out mature timber and left mountainous piles of debris down to very low elevations. Check out the insane photos of the size 4 in this MIN from the neighboring Sea to Sky region on January 15th. Avalanches of this scale wouldn't be surprising during the current warm weather. Parts of the region are currently under a Special Public Avalanche Warning (SPAW). Check out this new blog post for additional information.
Above 1500 m, 15-30 cm of recent snow is becoming moist at elevations experiencing above zero temperatures and on aspects that see the sun. The recent snow sits over the widespread January 16 melt-freeze crust which extends into alpine elevations. In the south of the region, this crust is one of many in the upper snowpack. There have also been reports of a layer of small surface hoar above the Jan 16 crust in the north of the region on polar aspects at treeline and in the alpine but this does not seem to be widespread. Wind slabs linger 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.
