Regions
South Coast Inland.
Conditions are primed for people triggering avalanches, which are expected to get bigger and more touchy with more snow and wind, and warmer temperatures. Deeper persistent slab problems are a real concern in northern parts of the region.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
TUESDAY: Mainly cloudy with light flurries in the afternoon bringing trace amounts during the day and 3-8 cm overnight into Wednesday accompanied by strong to extreme southwesterly winds. Freezing level to 500 metres with alpine temperatures around -10 C.WEDNESDAY: Mainly cloudy with scattered flurries bringing around 5 cm of new snow. Strong westerly winds and freezing level to 1000 metres with alpine temperatures around -5 C.THURSDAY: Mainly cloudy with flurries bringing around10-15 cm of new snow. Strong southwesterly winds and freezing level to 1500 metres with alpine temperatures around -5 C.
Avalanche Summary
Reports from the weekend include one observation of a natural wind slab (size unknown, likely 1-2) on a northeast aspect in direct response to wind loading from the southwest, as well as strong northeasterly winds causing multiple natural avalanches up to Size 2 on lee aspects at treeline and above in the Duffey Lake area.Reports from last week and over the weekend include at least three persistent slab avalanches up to 1.5 m deep and Size 3 destructive potential in the Duffy Lake and Hurley Pass areas. The failure planes of each slide remain uncertain, but the early February surface hoar layer was suspected in at least one occurrence and facets in another.While wind slabs remain an ongoing concern throughout the region a low-probability/high consequence avalanche problem should be driving a more cautious approach to backcountry travel, particularly in the northern parts of the region.
Snowpack Summary
10-35 cm of recent snow (with the greatest accumulations in the Cascades) has been blown into touchy wind slabs by southwest an more recent northeasterly winds, which are bonding poorly to facets and buried surface hoar, as well as crust on previously sun-exposed slopes. Reports from the Duffy Lake area on Sunday include easy whumphing and cracking observed at ridge top. The widespread mid-February crust can be found down 20-60cm and seems to be well-bonded, although it has been faceting and weakening recently. In the northern part of the region, a facet/surface hoar weakness buried early February, is now down 60-100 cm and remains reactive in snowpack tests. It is also suspected as the failure plane in at least one of two recent large persistent slab avalanches in the Hurley Pass area. In the Cascades, the mid and lower snowpack are well settled and strong.
Problems
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.