Regions
Vancouver Island.
Numerous small wind slab avalanches were triggered with ski cuts during avalanche control throughout the day Thursday at Mt Washington up to size 1 on the lee side (NW) of terrain features along the treeline ridges.
Past Weather
Light to moderate amounts of new snow has fallen since Tuesday night (approx 5-10 cm). Strong SE winds resulted in significant snow transport to NW aspects during the day Thursday Feb 18th. Temps climbed to near 0 Wednesday afternoon at 1500 m but returned to cold Thursday (-2 to -6).
Weather Forecast
Wind wind wind a significant warm up Sunday, all with moderate to heavy amounts of new snow. Winter is not done with us yet!Note the forecast for new snow over the next three days shows significantly high numbers for the west coast and north island vs the east side so factor this in to your decision making process. Friday - 2-5 cm of new snow for the east side, 5-10 cm for the north, 10- 20 cm for the west. Winds moderate to strong SW. Temps for 1500 m -4 to -6. Freezing levels 400 to 800 m. Saturday - 1-3 cm for the east, 5-10 for the north and west. Winds Strong to moderate SW. Temps for 1500 m -4 to -8. Freezing levels 300 to 800 m. Sunday - 10-15 cm for the east side, 30-55 cm for the north and west side of the island. Winds Strong to Extreme SW. Temps WARM -1 to +1. Freezing levels 1000 to 1800 m.
Terrain Advice
Avoid wind loaded zones on NE to NW asp near/below ridgelines Keep track of rising temps Sunday as this will certainly make the snowpack more sensitive to triggering. Avoid ALL avalanche terrain when the danger rating is HIGH, stick to low angled slopes and or well forested terrain.
Snowpack Summary
A slight warm up Wednesday resulted in moist snow surfaces in the PM on solar aspects at lower elevations. This moist snow then froze overnight creating a thin crust. Note non solar aspects escaped the warming. Strong SE winds Thursday resulted in significant snow being transported to lees stripping the 5-10 cm of new snow as well as the old storm snow from last weekend (15-20 cm of low density snow). The persistent weak layers that still linger in the mid snowpack now sits approx 70-110 cm down and have been unreactive to snow travelers.
Snowpack Details
- Surface: Heavily wind affected with widespread wind slabs on lees N-W, some windward zones stripped to a old crust.
- Upper: 5-10 cm of new snow (over a thin crust on solar aspects) over the 15-20 cm of light snow from the weekend
- Mid: A old crust sits on well settled snow above the persistent weak layers (facets and at lower elevations some hoar)
- Lower: Well settled
Confidence
High - Good field data collected, weather models in agreement. Few reports from the public over the past two days.
Problems
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.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
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.