Destructive persistent weak layers should still be on your radar if you're heading to the north of the region. Also, keep an eye on new snow amounts and how well this new snow is bonding.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
Tonight and Sunday: Periods of snow. 5-10 cm tonight and 10-15 cm on Sunday (snow looks heaviest in the northern part of the region). The freezing level is around 600-900 m. Winds are moderate from the S-SW easing to light. Monday: Cloudy with flurries and clearing. The freezing level is around 500-700 m and winds are light from the SW. Tuesday: Mainly sunny. The freezing level remains near 500 m and winds are light and variable.
Avalanche Summary
On Thursday, slab avalanches to size 3.5 were observed on a variety of aspects and elevations. These occurred in response to heavy storm loading from rain and snow. The mid-January surface hoar was the suspected culprit in many of these avalanches. Of note was a size 4 slab avalanche in Steep Creek in the Duffey Lake area. Moving forward, cooling will likely put a cap on persistent slab avalanche activity, except on higher elevation slopes in the north of the region where reactivity is expected to persist. Forecast wind and snow could create fresh touchy wind slabs in exposed lee and cross-loaded terrain this weekend.
Snowpack Summary
Convective precipitation delivered variable new snow amounts to the region on Friday. In the south, as much as 40 cm of snow may have accumulated, while further north there may have only been 10-15 cm. This new snow likely rests on moist/wet snow or a hard rain crust depending on elevation. A storm earlier in the week created deep and dense storm slabs in high elevation terrain and cause substantial cornice growth. Where it still exists, the mid-January surface hoar layer is between 60 and 130 cm below the surface. The combination of heavy storm loading and warm temperatures has likely flushed out this weak layer in many areas; however, I would still exercise caution on higher elevation slopes in the north of the region where continued reactivity at this destructive interface is likely to persist.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.