Slab overtop buried surface hoar is producing less frequent but larger avalanches at lower elevations and wind slabs are the main concern up high.
Weather Forecast
Westerly flow bringing light amounts of snow today. Pacific frontal system arriving to the region this evening, expecting moderate amounts overnight with associated strong west winds. Lingering flurries on Monday and dry conditions are forecast for Tuesday.
Snowpack Summary
Top 30cm low density snow. Localized Feb 15 drizzle crust down 20-30cm. Feb 12 surface hoar(SH)/crust layer is down 40-50cm. Fracture line profile on size 2.0 avalanche, Mt Fidelity, showed the Feb 12 bed surface layer as SH size 3-7 on a 3cm crust. Moderate sudden planar compression test results and a Rutschblock 3 whole block on that layer.
Avalanche Summary
From yesterday: 5 natural slab avalanches ranging in size 2 to 2.5 east of the Rogers Pass summit.From Feb 22: Skier controlled size 2.0 slab avalanche on Mt-Fidelity, 33-40deg, south aspect, down 35-45cm, 1700m, 100m wide, 120m long
Confidence
Due to the number of field observations on Sunday
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.