Be aware of conditions that change with elevation and expect touchy fresh storm and wind slabs at higher elevations.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Saturday
Weather Forecast
FRIDAY: Unsettled conditions with isolated flurries, moderate becoming light southwesterly winds and freezing levels dropping to 1500 m.SATURDAY: Cloudy with flurries bringing another 5-10 cm overnight, light winds and freezing levels around 1300 m.SUNDAY: Cloudy with light flurries, light southerly winds and freezing levels around 1400 m.
Avalanche Summary
Reports from Wednesday and Thursday morning include continued natural loose wet avalanche activity up to Size 2 at treeline and below. On Tuesday a 70 cm deep by 200 m wide Size 3.5 natural storm slab avalanche was reported that ran 1000 m from a south facing alpine start zone. On Sunday, explosives triggered numerous storm slabs up to size 2.5 as well as two deep persistent slabs up to size 3.5 which released down 200 cm, most likely on the November crust. Touchy new wind slabs are sensitive to light triggers and have the potential to step down and trigger persistent slab avalanches.
Snowpack Summary
Expect to find 15-20 cm of fresh snow blown into touchy wind slabs at higher elevations, and wet and cohesionless rain-soaked snow at lower elevations, which should soon freeze into a solid crust. Rapidly settling storm snow from last week is still bonding poorly to the previous snow surface from early February, which is now down 60-80 cm and includes a sun crust on steep sun-exposed slopes, faceted snow, as well as surface hoar on sheltered open slopes. A persistent weakness buried mid January is now down 80-150 cm and the November crust is down around 200 cm. These deep persistent weaknesses appear to be waking up with the warmer temperatures and several avalanches have recently released up to 2 m deep.
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.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.