We're expecting rapid loading to give way to a widespread natural avalanche cycle over the next 48 hours as each 12-hour period ushers in another 10 to 20 cm of snow accompanied by strong southwest wind. Avoid all avalanche terrain at this time.
Cornices are most prone to failure while they're growing, and we're expecting strong southwest wind along with a significant amount of snow. When large chunks of cornice fail there is potential for deep slab avalanches as evidenced by recent activity.
Fresh snow and wind adds to an already serious avalanche problem. By Wednesday morning up to 20 cm of new snow and 60 cm of older snow (for a total of 80 cm) may be resting on well-preserved surface hoar at and below treeline. This kind of setup could open the door to a situation where it "goes electric" as deep avalanches run naturally in sheltered terrain at and below treeline. Even deeper slabs are expected in the alpine as strong southwest forms thick wind fuelled storm slabs. Solar aspects (those that face south and west) have a buried crust that could serve as a bed surface for very large avalanches.
Batten down the hatches, the storm train is coming.
TUESDAY NIGHT: Freezing level around 500 m, strong southwest wind, 10 to 20 cm of snow.
WEDNESDAY: Overcast, freezing level rising to about 1000 m, strong southwest wind, 10 to 20 cm of snow during the day with another 5 to 15 cm Wednesday night.
THURSDAY: Overcast, freezing level holding around 1000 m, strong southwest wind, 10 to 20 cm of snow.
FRIDAY: Overcast, freezing level holding around 1000 m, moderate southwest wind, 1 to 5 cm of snow.
Natural avalanche activity is expected to be widespread Wednesday as new snow and strong southwest wind come together across the region.
On Monday in the Ningunsaw zone a natural cornice failure resulted in a very large (size 3.5) deep persistent slab avalanche on a south/southeast facing feature. Another large cornice failure was also noted. A small human triggered wind slab avalanche was reported on a north facing alpine feature too.
On Sunday a few different observations of the avalanche cycle that occurred during (Feb. 21) and just after the last storm emerged. Natural avalanches were widespread to size 2.5 at all elevations, likely running on facets and surface hoar. Explosive control work Sunday produced avalanches to size 2.5 at alpine and treeline elevation bands.
Glide crack openings and failures continue to be reported (almost daily) too.
We're expecting 10 to 20 cm Tuesday night and another 10 to 20 cm Wednesday accompanied by strong southwest wind. Widespread natural storm slab avalanches are expected. This snow adds to the 40 to 70 cm of storm snow that the last storm left in it's wake. There is potential for "step down" avalanche activity as the fresh snow interacts with the 50 to 80 cm deep "old" storm slabs that overly a couple layers of surface hoar that may be found in sheltered terrain at and below treeline or a melt-freeze crust on sun-exposed aspects.
A thin layer of weak and sugary faceted grains that formed in January may be found about 120 to 170 cm deep, and an early-season melt-freeze crust lingers at the base of the snowpack. These layers produced a few large natural avalanches in early-February and were largely nonreactive until the Feb 24th avalanche listed above was reported. This kind of storm has the potential to produce some very large avalanches as the snowpack is rapidly loaded.
