Confidence
Fair - Timing, track, or intensity of incoming weather is uncertain on Sunday
Weather Forecast
Friday night and Saturday: A bit of a precipitation break with moderate winds with strong gusts from the NW friday night. Another unsettled air mass will bring more precipitation on the region on Saturday but no significant amounts. Light W winds gusting moderate in the afternoon and surface freezing level and seasonal temperatures in the alpine (-5 to -10 C). Sunday: Similar pattern with possibly more precipitation, moderate W winds, cooler temperatures (down to -12 C). Monday: Arctic front tracking towards the region bringing more light to moderate precipitations and even cooler temperatures.
Avalanche Summary
A few natural slab avalanches were reported size 2 on E-NE aspects in the storm snow. A few small slabs were also triggered by skiers on the early January surface hoar found under 60-70 cm below treeline on a North facing aspect.
Snowpack Summary
From 15 to 30 cm of snow fell with the last 2 systems with light to moderate S-SW winds in the alpine and with relatively warm temperatures at low elevations. Storm slabs are found at all elevations. In the alpine, it is expected that the bond between these slabs and the underlying surface will improve, however they are gaining propagation potential with the continuing settlement. In other words, they could become harder to trigger, but if triggered, they will generate bigger avalanches. The new snow is also sitting on a couple of weak layers; a suncrust on S facing slopes and on a surface hoar layer mostly found below treeline. The bond of the new snow with these layer is now weak and it usually takes longer to improve and is harder to predict. It is therefore important to keep monitoring their location and reactivity to ski and snowpack tests. The early January surface hoar layer down 70-90 cm, also in the below treeline band, is becoming less of a concern to professionals but has recently been reactive to skier traffic in the South part of the region (see avalanche summary section).
Problems
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.
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.