Strong winds and new snow are building fresh windslabs and burying evidence of previous activity. Human triggering remains a serious concern in avalanche start zones that have not had activity in the past week.
Weather Forecast
An upper level northwest (Aleutian) flow is pushing a couple of cold fronts through our area on Wednesday. Up to 10-15cm of snow is forecast, with strong SW switching to light NE winds and seasonal temperatures. Thursday we will see a bit of a break in the precip, and possibly some sun. On Friday more snow is forecast.
Snowpack Summary
5-10cm of new snow has been blown in to fresh slabs by moderate to strong SW winds. These wind slabs overlie a settled upper snowpack which is sitting on the persistent weak layers in the mid snowpack. Many slopes had avalanche activity on these weak layers during last weeks storm, slopes without previous activity remain suspect.
Avalanche Summary
A couple of fresh slab avalanches (likely failing on a persistent mid snowpack weakness, and up to size 2) were observed by field teams at treeline elevations on Tuesday - likely triggered by significant wind transport and warming temperatures.
Confidence
Forecast snowfall amounts are uncertain
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.