Fresh shallow wind slabs and sluffing should be manageable Saturday, but we can't forget about the potential for large human triggered persistent slab avalanches that seem to be most reactive on south facing terrain at upper elevation.
Summary
Confidence
Moderate - Forecast snowfall amounts are uncertain on Saturday
Weather Forecast
The struggle between "spring-like" and "Arctic-like" will continue for a few more days. Saturday's storm should deliver a nice refresh of snow with the highest amounts concentrated in the southern portion of the region. A more spring-like pattern begins to take shape on Sunday with freezing levels creeping towards 2000 m by Monday.SATURDAY: Overcast, freezing level beginning near valley bottom rising to around 1500 m, light to moderate south/southwest wind, 2 to 10 cm of snow possible. SUNDAY: Broken cloud cover, freezing level beginning near valley bottom rising to about 1700 m, light to moderate westerly wind, 1 to 3 cm of snow possible. MONDAY: Scattered cloud cover, freezing level beginning around 1500 m rising to about 2000 m, light to moderate westerly wind, trace of snow possible.
Avalanche Summary
On Thursday warming temperatures initiated large loose wet avalanches to size 3 on south facing aspects between 2100 and 2700 m in the neighboring Glacier National Park. A small shallow wind slab was accidently triggered by a skier on a steep/unsupported east/southeast facing feature at 2200 m too.On Tuesday a skier remote triggered a size 2 avalanche on an east facing slope at 1700 m. The avalanche had a crown depth of 50 m running on the March 29th crust. A natural size 2 wind slab from a northwest facing slope at 2500 m was also reported.On Monday a size 3 persistent slab avalanche was remotely triggered by explosive control work. Numerous small (size 1-1.5) and reportedly hard wind slabs were also triggered on various aspects with both explosives and ski cutting. One large (size 2.5) natural cornice fall was reported as well.
Snowpack Summary
Warming temperatures and time have helped to settle the upper 30 to 40 cm of ageing storm snow and have formed a weak surface crust on all aspects aside from true north below 2000 m. This crust extends up to around 2500 on south facing slopes. On north facing slopes above 2000 m, temperatures have remained cold and the snowpack is still quite "winter-like."The main concern is the mid-March Persistent Weak Layer (PWL) which is now 60 to 100 cm below the surface. This layer is composed of a crust on all aspects at low elevations. At upper elevations the layer presents as a crust on solar aspects (those that face south and west) and buried surface hoar on polar aspects (those that face north and east). The reactivity of this interface has been steadily decreasing, but it continues to produce large avalanches and the potential for deep 'step down' avalanches cannot be dismissed. Solar aspects are expected to be the most suspect as the freezing level begins to rise over the next few days.Deeper persistent weak layers from January and December are still being reported by professional observers, but are generally considered dormant.
ghelgeson,
Avalanche Canada
