Avalanche Forecast

Out of the frying pan and into the fire, it looks like we’re in for another series of significant storms this week.

SUNDAY NIGHT: Freezing level around 1000 m, strong to extreme west/northwest wind, 5 to 15 cm of snow possible.

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 700 m, strong southwest wind, 10 to 20 cm of snow possible during the day, 5 to 10 cm of snow possible Tuesday night.

WEDNESDAY: Overcast, freezing level beginning at valley bottom rising to 600 m, moderate west/southwest wind, 1 to 5 cm of snow possible.

On Saturday cornice failures were sensitive to explosive control work and skier triggering to size 2.5. Control work also produced a size 3 persistent slab avalanche that stepped down to the January facet layer on a northeast facing slope at 1500 m. 

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:

Saturday: A natural size 2 avalanche was observed on two different aspects of a steep alpine feature, likley running on the February 19th surface hoar.

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.  

As of 15:00 Sunday 10 cm has fallen across the region with moderate wind out of the west and northwest.

Last week's storm was a doozy, when combined with the previous storm, a total of 60 to 130 cm of snow fell 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 1000 m a crust can be found just under the new snow 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, another very large avalanche on February 24th, and then a very large explosvie triggered avalanche on February 29th.

• Watch for changing conditions today, storm slabs may become increasingly reactive.
• Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
• Be aware of the potential for remote triggering and large, deep avalanches due to the presence of buried surface hoar.
• Avoid exposure to slopes that have cornices overhead.