The storm is expected to bring strong winds and rapidly rising freezing levels. Expect avalanche danger to increase as the storm develops. If you see more than 25cm of new snow tomorrow, expect your local avalanche danger to be HIGH.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The storm system is expected to bring around 15mm of precipitation to the south of the Cariboos region on Tuesday and 5-10mm to the north of the region. Winds are expected to be strong from the SW and freezing levels will climb as high as 2000m by Tuesday afternoon. On Wednesday and Thursday, freezing levels should remain around 2000m and winds will remain moderate or strong in the alpine. There is currently some uncertainty regarding precipitation amounts for Wednesday and Thursday with models currently showing another 10-30mm.
Avalanche Summary
The storm snow is reactive to ski cutting and is producing isolated avalanches up to size 1. I expect wind loaded areas in the alpine to be the main concern at the moment but this will become more widespread as the storm progresses.
Snowpack Summary
Around 15-30cm of new snow sits on a weak layer of surface hoar. Reports from the region suggest that anywhere from 50-150 cm of settling snow overlies one or more weak layers which formed during November. Snowpack tests suggest that these weak layers are getting harder to trigger but still have the potential to produce large avalanches if triggered. Recent wind has created wind slabs in lee features in exposed alpine terrain.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.