It's heads up hockey out there folks. We have a deeply buried surface hoar layer that continues to show its ferocity by producing very large natural and human triggered avalanches. Time to seek out the simple terrain options free of overhead hazard.
A rather volatile layer of buried surface hoar is 60 to 130 cm below the surface. This layer continues to produce very large natural and human triggered avalanches. Large cornices that loom over many slopes are on the brink of failure. Failing cornices are likley to produce large avalanches when they impact slopes.
Sunday's storm snow and strong southwest wind is expected to form fresh sensitive slabs at all elevations. Storm snow will likely come to rest on yet another layer of surface hoar which is expected to allow for touchy new storm slabs.
Out of the frying pan and into the fire, it looks like we’re in for another series of significant storms this week.
SATURDAY NIGHT: Freezing level at valley bottom, light northwest wind, trace of snow possible.
SUNDAY: Overcast, freezing level rising to about 1000 m, strong southwest wind, 5 to 15 cm of snow possible during the day with another 5 to 15 cm Sunday night.
MONDAY: Overcast, freezing level rising to about 1000 m, strong west/southwest wind, 5 to 15 cm of snow possible during the day, 10 to 20 cm of snow possible Monday night.
TUESDAY: Overcast, freezing level around 900 m, strong southwest wind, 10 to 20 cm of snow possible during the day, 5 to 10 cm of snow possible Tuesday night.
The February 19th surface hoar is widespread, touchy and continues to produce both natural and human triggered avalanches. Here's a recap of some of that history, this list isn't exhaustive but it shows a trend:
Friday: Natural avalanches to size 3 in terrain between 1400 and 1600 m. Crown depths 60 to 100 cm on north, northeast and east facing terrain features. There was also a skier remote triggered size 2.5. The suspected failure plan for all of this activity is the February 19th surface hoar.
Thursday: Natural avalanches to size 3 were observed in steep alpine terrain.
Despite the poor visibility, several size 2-2.5 slab avalanches were reported in alpine terrain on Wednesday.
On February 24 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.
Glide crack openings and failures continue to be reported (almost daily) too.
Last week's storm was a doozy, when combined with the previous storm, a total of 60 to 130 cm of snow has fallen in the past week. This snow is resting on a layer of surface hoar that was buried on February 19th. This layer seems to be quite widespread and remains sensitive to human triggers. On solar aspects (south through west) this surface hoar may be resting on a buried crust which could be a very problematic setup.
Below about 1800 m a crust can be found on the surface due to recent warm temperatures and rain.
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 linger at the base of the snowpack. These layers produced a few large natural avalanches in early-February and then another very large avalanche on February 24th.
