Strong wind and over 6" of new snow for the mountains near the crest will create reactive wind slabs on upper elevation, exposed slopes. Below treeline, rain on snow may cause small loose wet avalanches on very steep slopes. Stay alert to changing conditions throughout the day, and be ready to avoid wind-loaded slopes steeper than 35 degrees.
Rain on snow up to around 4,000ft may initiate a round of small, loose wet avalanches on very steep slopes. Look for signs of loose wet activity such as rollerballs, and other small fan shaped avalanches as the daytime progresses. Don't let these small sluffs catch you by surprise in or around terrain traps.
Example small, loose wet avalanche.
Strong westerly winds and will transport new snow onto lee slopes during the daytime. Winds may transport new snow further downslope or below ridgelines than usual. While most wind slabs will likely be shallow, deeper slabs are likely to build closer to the Cascade crest. The likelihood and potential size of wind slabs will increase by afternoon. Look for signs of instability such as shooting cracks, and stiffer textured snow over weaker snow. Feel for textured wind-affected snow as you change aspect and elevation. For the most part, avalanche activity should be confined to new snow, but avalanches could step down to recent storm layers and weak snow over a crust 1.5-2ft deep above treeline.
During the last bout of snowfall on Sunday night, cornices broke off and released onto slopes, triggering shallow slab avalanches. Expect similar conditions on Wednesday. If traveling along ridgelines with large cornices make sure to stay well away from the edge. Travelers are surprised every season when cornices break further back than they expect.
(3/22/2021) Small wind slab release on a test slope. Notice the rippled texture to the snow surface.
Snowfall will start in the morning and by mid-afternoon around 6 inches of new snow may accumulate near the Cascade crest. New snowfall amounts should taper off for areas further east. Strong westerly ridgeline winds will last through the day. New snow will be falling on a mix of suncrusts on east to south to west aspects, and cold dry snow surfaces on northerly aspects. On Monday, I went out to Van Epps Pass area, and found around 8" of new snow. We stayed off of steep slopes that appeared thickly wind-loaded near ridgelines. The new snow and wind will potentially add to these slabs on Wednesday.
A crust and adjacent weak layer formed in mid-January can still be found about 2-6 feet below the surface throughout most of the zone. Several different avalanche cycles released down to this interface, with the last cycle producing avalanches up to size D4. Avalanches down to this layer are now unlikely with the last known avalanche down to the mid-Jan crust/facet combo recorded on March 1st. We're watching the upcoming weather pattern for major warm-ups or storm events to see when and if these deeper layers will be tested again. The most suspect areas for deep persistent slabs are shallow, rocky, and unsupported slopes, especially where overhead cornice fall could trigger avalanches.
