Variable amounts of new snow throughout the region has been redistributed by recent southwest switching to southeast wind. Additionally when the sun comes out this time of year it usually packs a punch - steep southerly slopes are suspect right now.
Summary
Confidence
Moderate - Forecast snowfall amounts are uncertain on Saturday
Weather Forecast
SATURDAY: Flurries, accumulation 5-15cm Friday night into Saturday / Light east wind / Alpine temperature -8 SUNDAY: Cloudy with isolated flurries / Light west wind / Alpine temperature -7 MONDAY: Mix of sun, cloud and isolated flurries / Light to moderate west wind / Alpine temperature -8 NOTE: The convective flurries which are common during this time of year can result in widely varying snowfall amounts throughout a region. These spring squalls routinely drop 20+ cm of snow in one valley while the adjacent drainage remains dry. For this reason, the distribution of avalanche problems associated with new snow, such as wind slabs, can vary greatly within a region.
Avalanche Summary
On Thursday there was report of naturally occurring size 2.5 persistent slab avalanche on northeast facing slope at 2400m. This was from a heavy trigger of glacial ice. Prior to that avalanche activity consisted of mainly wind slabs (skier triggered and skier remote) in the size 1-1.5 range. However, we've also received reports of persistent slab avalanches (to size 3) where recent accumulations have been the highest. These avalanches, were skier-triggered or remotely triggered (from a distance) on Monday and naturally occurring on Tuesday with wind loading on cross-loaded slopes. We suspect the buried sun crust buried mid-February. Deep persistent avalanche activity has become less frequent over the past week.
Snowpack Summary
Up to 50 cm of recent storm snow (in the south and west parts of the region) has been redistributed into wind slabs in wind-exposed terrain by south and southwest flow. Up to 60cm below the surface there's a layer buried mid-February that's a sun crust on solar aspects, and spotty surface hoar on sheltered slopes. This layer looks most concerning on on solar aspects where it's associated with with small facets or surface hoar above.There are several deeper layers that have shown signs of improving but still remain suspect as low probability - high consequence avalanche problems. We are talking about surface hoar layer buried back in December and January. Near the base of the snowpack is a November crust combined with loose sugary faceted snow. These layers may "wake-up" with strong inputs such as sustained warming, sustained snowfall, large triggers (e.g. cornice fall or smaller avalanches coming down from above); human triggering is also possible in shallow snowpack areas with convoluted terrain.
mbender,
Avalanche Canada
