Heavy snowfall on Friday will be accompanied by warming temperatures and Strong Westerly winds - prime material for slab building! If new snowfall amounts over Thursday/Friday exceed 35cm, consider danger HIGH at Treeline.
Weather Forecast
Two airmasses collide - snowfall amounts are tricky to predict.Thursday: Snow overnight (5-10cm), easing. Temperature inversion. Light SW winds.Friday: Snowfall, heavy in the West (20-45cm). Freezing level rising. Treeline High: -5. Winds rising to Strong W. Saturday: Sun & cloud, light snowfall later. Moderate SW winds. Treeline High -5
Snowpack Summary
Snow has fallen daily since February 25. Deep, low-density snow is forming Storm Slabs lee to SW winds above 1800m, where warm winds are riding over cold Arctic air in the valleys. The old snow surface from Jan 25 (small facets) is down 70-90cm. This layer may be reactive where it sits on a crust (Solar aspects, primarily at Treeline).
Avalanche Summary
Early in the week, a Large Cornice fall at Treeline triggered a slab in steep, lee terrain, resulting in a Large (size 2.5) avalanche. On Tuesday, forecasters easily ski cut Small (Size 1) Loose Dry avalanches in steep terrain. On Wednesday, Several Natural Storm Slabs (Size 1.5) were observed from NE-NW aspects at Treeline.
Confidence
Forecast snowfall amounts are uncertain on Friday
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.
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
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.