Heavy snowfall and strong winds have overloaded a persistent weak layer (PWL) of faceted snow down near the ground on mid and upper elevation aspects facing west through north and east. This weak layer formed from snow that fell earlier this Autumn, and once we buried this weak layer beginning on December 9, the PWL has become reactive with avalanching on every loading event of new snow and/or wind.

We have once again rapidly overloaded this weak layer with heavy snowfall and strong west/southwest winds, creating very dangerous avalanche conditions. On my field day yesterday in mid-elevations along the Big Cottonwood and Millcreek ridgelines, I was finding this weak layer to be very reactive to stability tests.

Avalanches failing on this weak layer may be triggered remotely (from a distance) or from below. Any avalanche failing on this PWL may break down 2-6' deep (possibly deeper) and propagate hundreds of feet wide.

The photo below shows the poor structure of strong snow over weak snow.

Heavy, dense snowfall from overnight and into today may create sensitive soft slabs of new snow, especially at the mid and upper elevations. The new snow will be especially sensitive during any period of high precipitation intensity. Although you may find the new snow sensitive on all aspects, the new snow will create very dangerous avalanche conditions on slopes facing west through north and east where slides may break up to 6' deep into old snow down near the ground.

Strong winds from the west and southwest have created dense slabs of wind-drifted snow on all aspects at the mid and upper elevations. Strong winds can channel snow around terrain features and create fresh drifts on all aspects, including well-down off of ridge lines. On mid and upper elevation slopes facing west through north and east, these drifts will overload the buried layer of weak faceted snow down near the ground.