The persistent slab problem is shifting into a low-probability/ high-consequence situation. Be confident in your local snowpack before committing to any big terrain.
Confidence
Fair - Timing or intensity of solar radiation is uncertain on Sunday
Weather Forecast
Light snow fall (5-15 cm) is expected on Saturday, petering to flurries on Sunday and Monday, with a chance of sun. The freezing level is around 1600 m by day, falling towards valley floor by night. Winds are generally light.
Avalanche Summary
Several cornice falls have been reported in the last few days, some of which have triggered slabs on slopes below.On Wednesday, a size 2 persistent slab was triggered in a permanently closed area at a ski area. It may have started in the March persistent weak layer before it stepped down to fail at ground. While the likelihood of triggering a large persistent slab avalanche has gone down, the consequences remain high.
Snowpack Summary
Recent 10-25 cm snow was shifted by variable strong winds into wind slabs on lee slopes above about 2000 m. Cornices are large and touchy in some spots. The new snow sits over various crusts which formed recently. Low elevations sport an isothermal snowpack, which is now be capped by a refrozen crust.Persistent weak layers in the upper snowpack remain a concern. In the north of the region, the mid-March crust/facet layer is down 40-60cm. The mid-February crust/facet/surface hoar layer, down about 80 cm, may also still be reactive in isolated areas. Weak layers which formed earlier in the winter are also a concern in certain spots.
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.