Deep persistent weaknesses are still reactive in snowpack tests. Very large avalanches are still possible.
Weather Forecast
Unsettled weather is expected to bring a mix of sun and cloud with isolated flurries on Thursday, before a more organized system brings 5-10 cm of snow on Friday and another 3-5 cm on Saturday. Freezing levels are expected to hover around 1500 m for the forecast period and winds are expected to pick up to moderate southwesterlies during on Friday.
Avalanche Summary
Over the past few days, several natural wind slab avalanches to Size 2 were observed in the north of the region. Two of of the larger avalanches possibly stepped-down to the mid-March persistent weakness on north facing alpine slopes. Also reported were several loose sluffs to Size 1.5 in response to sun-exposure on south aspects.
Snowpack Summary
Another 10-20 cm of low density storm snow adds to the 30 cm of recent moist snow capped by a thin crust, that overlies a rain crust buried last Saturday. Reports suggest this crust exists up to about 2100m. West through southwesterly winds have shifted these new accumulations into touchy wind slabs in exposed terrain. A facet/crust persistent weakness buried mid-March is down approximately 50-100 cm and recently produced moderate sudden results in snowpack tests where it was found down 55 cm near the Duffey Lake Road. This remains the chief concern amongst avalanche professionals in the region due to it's potential for very large avalanches.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.