The storm may have ended, but a persistent avalanche problem still exists. Large and destructive avalanches are still possible.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Expect a mix of sun and cloud on Wednesday and Thursday morning. By late Thursday and Friday, a more organized front will bring about 10cm of new snow. Ridgetop winds should remain generally light from the northwest on Wednesday and Thursday, becoming strong from the southwest with Friday's system. Daytime freezing levels should hover around 1200m
Avalanche Summary
Over the past few days, several natural wind slab avalanches to size 2 were observed in the north of the region. In many cases, these wind slabs were triggered by cornice falls. We have not yet heard how persistent avalanche activity panned out in response to the recent storms. My best guess is that we may be transitioning into a lower probability-high consequence avalanche pattern with this persistent weak layer.
Snowpack Summary
Up to 30cm of recent snowfall overlies a rain crust that was buried on March 28th. Reports suggest this crust exists up to about 2100m. Strong southwest winds have shifted these new accumulations into wind slabs in exposed high elevation terrain, while rain has saturated the snowpack below about 1600m. The most critical snowpack layer in the region is a facet/crust interface which lies anywhere from 50-100 cm below the surface. This persistent weak layer (which is most prominent in the north of the region) was responsible for several naturally triggered avalanches to size 3 over the past week, and continues to produce sudden snowpack test results. Although the likelihood of triggering this layer has decreased somewhat, avalanches failing at this layer may not be survivable. At lower elevations, rain has saturated the snowpack. Layers below the critical mid-March interface are generally considered to be well-settled and strong.
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.