Watch for conditions that change with elevation. Heavy rain at lower elevations means heavy snow up high.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Thursday
Weather Forecast
THURSDAY: 5-10 mm of precipitation with moderate southwesterly winds and freezing levels around 2000 m.FRIDAY: Unsettled conditions with isolated flurries, moderate becoming light southwesterly winds and freezing levels dropping to 1500 m.SATURDAY: A mix of sun and cloud with flurries possible late in the day, light winds and freezing levels around 1300 m.
Avalanche Summary
Reports from Tuesday include continued natural loose wet avalanche activity up to size 1.5 on steep sun exposed slopes, as well as a 70 cm deep by 200 m wide Size 3.5 natural storm slab avalanche 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. Rain at lower elevations is expected to destabilize the upper snowpack resulting loose wet sluffing and potentially increasing the sensitivity of triggering persistent slab avalanches. In the alpine, touchy new wind slabs have the potential to step down and trigger persistent slab avalanches.
Snowpack Summary
Flurries have resulted in light amounts of fresh snow at higher elevations, while elsewhere the snow surface has become wet, loose and cohesionless on sun-exposed slopes and at lower elevations. 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. Recent strong winds from the south and west had redistributed the recent storm snow in exposed terrain forming wind slabs. 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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.