Avalanche Forecast

A series of fronts hit the region Monday night, Tuesday night, and Thursday.

MONDAY NIGHT: Heavy snow with 10-20 cm, strong to extreme wind from the west, freezing level drops from 1000 to 500 m.

TUESDAY: Light snow in the morning then intensifying in the afternoon with accumulations of 10-25 cm throughout the day, strong southwest wind, freezing level around 500 m with alpine temperatures around -4 C.

WEDNESDAY: Cloudy with 5-15 cm of new snow by the morning and light flurries with another 1-5 cm throughout the day, moderate southwest wind, freezing level around 500 m with alpine high temperatures around -5 C.

THURSDAY: Yet another frontal system brings 20-40 cm of snow, strong to extreme wind from the south, freezing level around 800 m with alpine high temperatures around -3 C.

Stormy weather since Sunday has limited observations, but there has likely been a natural cycle of storm slab avalanches at higher elevations that will continue into Tuesday.

Throughout last week's storms there were numerous reports of large avalanches, many of which failed on persistent weak layers including the widespread February 19th surface hoar. Here's a recap of some of that history, this list isn't exhaustive but it shows a trend that is expected to continue this week:

• Saturday: A natural size 2 avalanche was observed on two different aspects of a steep alpine feature, likely running on the February 19th surface hoar. Explosive control triggered a size 3 persistent slab avalanche that stepped down to the January facet layer on a northeast facing slope at 1500 m.
• 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 was the February 19th surface hoar.
• Wednesday and Thursday: Natural avalanches to size 2-3 in alpine terrain. 
• February 24: A natural cornice failure in the Ningunsaw zone resulted in a size 3.5 deep persistent slab avalanche on a southeast facing slope.

Large cornice and glide crack failures continue to be reported (almost daily) too.  

New storm slabs will form throughout the week with significant snow and wind in the forecast. Another 20-40 cm is expected between Monday and Tuesday afternoon, which will add to 15-30 cm from Sunday. This all sits above a layer of surface hoar that was buried on March 1st, which will likely make for extra reactive storm slabs. Another widespread layer of surface hoar that was buried on February 19th is now 100-150 cm below the surface and has been sensitive to human triggering over the past week. 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 recent 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.

• Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
• Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time.