Regions
Northwest Inland.
Confidence
Fair - Due to variable snowpack conditions
Weather Forecast
Monday: Expect clouds to build, with snow beginning late in the day. Winds should start northerly, but turn to strong southwesterlies as the system advances. Up to 5cm are possible with daytime temps reaching -10. Tuesday & Wednesday: The storm should subside early in the day and skies will remain unsettled through Wed. Temperatures should reach -8 each afternoon under southwesterly winds.
Avalanche Summary
Natural avalanches to size 2.0 and rider triggered to 1.5 have been reported. In isolated areas with no wind effect, the new snow is sluffing.
Snowpack Summary
Between 10-30cm of new snow fell in the most recent storm pulse. This adds to the previous storm snow, with 45-60 cm being an average amount over the mid February layers. Recent, intermittent clear skies have created a sun crust on south facing terrain into the alpine.The mid February layers are a strong melt freeze crust at lower elevations (below 1000m) and wind effected snow higher in the alpine while between these elevations, the interface varies wildly from facets, surface hoar, sun crust or wind press. The surface hoar is not widespread but is responsible for much of the recent avalanche activity. With the additional wind loading, pockets as deep as 70cm are possible on lee features. To compound the wind slab issue, recent winds have been northerly, building reactive slabs on south facing terrain features. The mid and lower snowpack is generally well settled and strong.
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.
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.