Rising temperatures and intense solar radiation is the driving force for the Avalanche Danger Ratings on Saturday.
Weather Forecast
Saturday: The dominating ridge of high pressure will bring significant warming and sunny skies. Alpine temperatures could get as high as plus 4.0 degrees with freezing levels rising near 2400 m and sunny skies. Ridgetop winds will be light from the SW.Sunday: The ridge will weaken, allowing the next frontal system to move in. Skies will generally be cloudy and no significant precipitation is expected. Alpine temperatures will fall to -3.0 and freezing levels will be near 1300 m. Ridgetop winds will blow moderate from the SW.Monday: Unsettled conditions with snow amounts up to 10 cm. Ridgetop winds will be light from the SW. Alpine temperatures near -4.0 and freezing levels hovering at 1300 m in the afternoon.
Avalanche Summary
No natural avalanche activity has been reported.On Thursday, numerous natural slab avalanches size 1.0-2.5 on NE-E aspects, one being a cornice release, and others releasing on older buries surface hoar layers. Rider triggered size 1.0 on SE aspect at 1500 m on most recently buried surface hoar/crust interface. With forecast rising freezing levels and a high solar influence, loose wet avalanches are likely.
Snowpack Summary
Wind slabs can be found behind ridges, ribs and on lee slopes (NW-NE).The upper snowpack is showing continued settlement and gaining strength, although above zero alpine temperatures and sunny skies will likely weaken it. Down 20-50 cm sits a persistent interface comprising of crusts, facets and surface hoar crystals. Recently, this layer has been touchy in sheltered areas at treeline and below (where the surface hoar had a chance to form). Down deeper sits another surface hoar layer (40-80 cm) which seems to be gaining strength with very little recent reactivity on it.The mid pack is generally well settled, which may be bridging a basal facet/crust layer in deeper snowpack areas. The average snowpack depth at treeline is near 180 cm.
Problems
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.
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.