Regions
Northwest Coastal.
An extremely conservative approach is essential Monday!
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain on Sunday
Weather Forecast
Synopsis: The weather for the next 24 hours is super complex. The bottom line is that the NW coast is going to get hammered by southwesterly flow. The models suggest that the most extreme warming will be west of Terrace where the freezing level is forecast to go to 2000m Sunday. Bear Pass is forecast to see a freezing level of 900m. As a result, I'm going to issue a Wx for Kasiks and then a separate Wx that should be closer to a regional average for the rest of the NW Coastal Region.Kasiks:Sunday: Freezing Level: 2300m Precip: Snow & Rain, heavy at times 15 /25mm 30 /50cm Wind: Mod gusting Extreme, SWMonday: Freezing Level: 700m Precip: 5/10mm 10/20cm Wind: Mod gusting Strong, W Tuesday: Freezing Level: 700m Precip: 1/5mm - 2/10 cm Wind: Lht W occasionally gusting Strong.Regional Average:Sunday: Freezing Level: 700m 1000m Precip: Snow & Rain, heavy at times 15 /25mm 30 /40cm Wind: Mod gusting Extreme, SWMonday: Freezing Level: 700m Precip: Trace Wind: Strong, W Tuesday: Freezing Level: 700m Precip: Trace Wind: Lht W occasionally gusting Strong.
Avalanche Summary
On Friday the region saw a storm cycle that averaged Size 2.0 with one natural 3.0 reported from a steep start zone. Lot's of loose snow moving on Friday too.
Snowpack Summary
Total snowpack depth in the region ranges between 150 - 250cm. On December 20th Kasiks (Between Terrace & Rupert) picked up almost 50cm while Bear Pass saw around 20cm. This snow rests on a variety of old surface layers: old wind slabs, a crust that formed on Dec. 14 in some locations and even small grained surface hoar. This brings the total load of snow on the December 12 layer to 75 - 130 cm. December 12th is a surface hoar/facet combo formed during the early December cold snap which rests on old wind slabs and melt freeze crusts. Strong winds out of the South & West have been working overtime to redistribute storm snow from the past week into what is now a widespread wind slab problem at and above treeline.The mid pack is composed of various faceted layers and crusts. A significant basal facet/crust combo lingers near the base of the snowpack and is most prevalent on NW - E facing aspects at the upper TL and alpine elevations.
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.