Regions
Northwest Coastal.
Lingering storm instabilities means conditions may remain tricky for a couple days. Rapid warming or sun may increase the likelihood of triggering a slab.
Weather Forecast
A strong warm ridge of high pressure sits over the SW part of the region while cold Arctic air sits to the NE. On Thursday, mostly cloudy conditions with periods of sun are expected across the region with light alpine winds. Freezing levels in the south of the region may reach as high as 3000m with the warmest layer of air sitting between 1500m and 2000m (+5 deg C or warmer possible). The north of the region should remain below zero but a temperature inversion is expected. On Friday, some of the above-freezing air may reach the north of the region but the valleys should remain cold. The inversion and warm air are expected to break down on Friday night and freezing levels should be around 500m on Saturday. Winds should remain light on Friday and Saturday. 4-8mm of precipitation are forecast for Saturday.
Avalanche Summary
On Tuesday, several natural size 2 avalanches were reported in the Terrace area. On Monday, natural and explosive triggered avalanches up to size 2.5 were reported in the central part of the region. Natural avalanches activity is expected to decrease on Thursday but isolated natural avalanches are possible. The potential for human triggering remains high on Thursday.
Snowpack Summary
Storm snow amounts vary across the region. Since the weekend, southern areas received 50-80cm of new snow and the north probably around half that. Strong winds are one common theme in all areas though. Ridge winds were cranking from the SE-SW stripping windward slopes bare and probably forming hard or dense wind slabs in lee and cross-loaded areas. A buried surface hoar layer down around 70cm may be more prevalent in northern sections like Bear Pass and Ninginsaw Pass. The mid December crust can be found down around 1m and is sandwiched with facets and surface hoar. The November crust down near the bottom of the snowpack is generally well bonded but is still reactive in some test profiles. The deeper snowpack weaknesses could 'wake up' with heavy loading from new snow and wind.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.