Regions
Northwest Inland.
This forecast was created using limited field data. If you are out in the mountains, please consider sending us your observations or posting on our new website.
Confidence
Poor - Due to the number of field observations
Weather Forecast
A frontal system is expected to bring around 10-15mm of precipitation to the North Coast inland on Tuesday. Another 5-10mm is possible Tuesday night into Wednesday morning. Freezing levels on Tuesday are expected to be 800-1000m with strong-to-extreme winds from the SW in the alpine. On Wednesday, precipitation should taper off in the morning with freezing levels around 500m and winds easing to moderate NW in the alpine. Christmas day looks to be a mix of sun and clouds with freezing levels near valley bottom and moderate winds in the alpine.
Avalanche Summary
We received a report on Sunday from the Hankin area of a natural size 1 slab avalanche. This occurred on a north aspect at treeline. The crown depth was around 20cm and it failed on the most recent rain crust. Check out the report here: https://goo.gl/WdmvxL
Snowpack Summary
The weekend storm slab is between 20-40 cm deep. Very strong winds have transported snow in the alpine and at treeline into pockets of windslab that may not be well bonded to the old surfaces. Below the new snow you'll likely find wind-scoured surfaces and old wind slabs in exposed terrain, and settled storm snow closer to treeline. Near the base of the snowpack, weaknesses such as the mid-November crust-facet layer are still of concern. I'd use extra caution around steep, unsupported high elevation terrain as avalanches at this interface could propagate over wide distances.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.