Watch for winds slabs in the alpine and treeline areas. Deeper and more reactive deposits will be in lee and cross-loaded terrain.
Confidence
Moderate - Wind effect is extremely variable
Weather Forecast
MONDAY NIGHT: Cloudy with clear periods and isolated flurries, trace to 5 cm accumulation. Alpine temperatures near -26C. Ridgetop winds moderate from the east-northeast.TUESDAY: Sunny with cloudy periods. Alpine temperatures near -15C. Ridgetop winds moderate from the northeast.WEDNESDAY: Sunny with cloudy periods. Alpine temperatures near -15C. Ridgetop winds light from the east-northeast.THURSDAY: Mix of sun and cloud with isolated flurries, trace to 5 cm. Alpine temperatures near -15C. Ridgetop winds light from the east.
Avalanche Summary
On Sunday, a skier triggered a size 1 storm slab avalanche on a north aspect around 2100 m. On Saturday, numerous natural and explosives triggered storm slab avalanches to size 2-2.5 were reported. These were 50-100 cm deep running on east through north aspects in the alpine and treeline. Loose, dry snow is sloughing in steeper terrain. Last Thursday, an explosive triggered a large (size 2.5) persistent slab avalanche. The slab was about 40 cm deep and failed on a southerly aspect between 1650 and 2000 m.
Snowpack Summary
The recent storm snow is setting out to around 40 cm and being redistributed by northeast winds, stripping exposed terrain in the alpine and upper treeline. Loose recent snow is still found in sheltered areas and lower elevations. The recent snow fell on wind affected surfaces in the alpine and treeline. In sheltered areas and lower elevations, the new snow is burying faceted surface snow and possibly a layer of surface hoar. In sheltered areas between 1600 and 1800 m, another weak layer of surface hoar crystals buried around Valentines Day, is now 60-80 cm below the snow surface.Two more weak layers of surface hoar may be found within the snowpack. One buried early-February, is 80-100 cm deep in shaded and sheltered areas above 1600 m. The other buried mid-January, is 100-150 cm down and is most prominent between 1600 m and 1900 m.The remainder of the snowpack is well-settled.
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.