Good skiing can be found in sheltered terrain.Persistent weak layers continue to show isolated signs of reactivity, this problem will likely persist for some time.
Weather Forecast
A westerly flow in the upper atmosphere is pushing a series of weak frontal systems over our area, giving cool temps and light flurries.Up to 5 cm of snow will fall overnight into Thursday, with moderate SW ridgetop winds (tapering to light mid-morming). Alpine temps will be cold, with an overnight low of -18C, and a daytime high of -10C.
Snowpack Summary
Recent storm snow has been blown in to a wind slab up to 30cm thick. This has added to the previous slab sitting on a sun-crust on solar aspects and facets on polar aspects - these are now buried as deep as 60cm. Underneath the variable slab in the upper snowpack, as well as in shallow areas, the snowpack is generally facetted and weak.
Avalanche Summary
On Tuesday, avalanche control at Marmot Basin using explosives produced several size 2 slab avalanches. These were on Northerly alpine slopes, and failed on persistent weak layers. A recent MIN report from the Bald Hills has a good photo of an avalanche that occurred on an alpine NE aspect (from the photo it looks to have been skier triggered).
Confidence
Due to the number of field observations
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.