Regions
Northwest Coastal.
Rain falling on snow will rapidly increase the avalanche hazard. Saturday's ratings will quickly jump to Sunday's ratings if/when rain begins to fall on Saturday.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Synopsis: Saturday offers a short break in the action before another frontal wave crashes into the mountains of the North Coast Saturday evening. Precip continues through the day Sunday as freezing levels rise, possibly as high as 1500 2000m Sunday evening. All bets are off for Sunday night. The bulk of the precip has the potential to fall as rain. Stay tuned for more info!Saturday: Freezing Level: Valley Bottom Precip: 1/5mm - 2/10 cm Wind: Lht W/NWSunday: Freezing Level: 1800m Precip: 35-40mm snow/rain mixed Wind: Mod gusting Extreme, SWMonday: Freezing Level: 1100m Precip: 3/6mm 5/10cm Wind: Lht gusting Mod, W
Avalanche Summary
There wasn't much avalanche activity reported from Thursday, likely due to the cooler temperatures. I'm guessing that we'll see a fair amount of avalanche observations from Friday with all of the new storm snow. During the first half of the week numerous size 2-3 avalanches were running naturally and with explosive assistance throughout the region on all aspects with the bulk of the activity occurring on N - SE facing aspects.
Snowpack Summary
Total snowpack depth in the region ranges between 150 - 250cm. On December 20th the region picked up almost 50 cm of new snow that 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 crust/facet combo lingers near the base of the snowpack.
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.