As stormy weather tapers-off and a dry ridge builds over the province, solar radiation will become the driver for natural avalanche activity. Watch your overhead hazard as avalanches could travel farther than anticipated.
Weather Forecast
A dry ridge of high pressure will develop over the region bringing clear skies for Thursday and Friday. Increased cloud is forecast for Saturday. Ridgetop winds will be light to moderate from the northwest on Thursday morning, and then become light for the rest of the forecast period. Freezing levels will hover around 1200m on Thursday, 1500m on Friday and 2100m on Saturday.
Avalanche Summary
Explosives control on the west/central part of the region produced slab avalanches to size 3 on Tuesday. In many cases, avalanches failed within the recent storm snow; however, a few of the bigger avalanches stepped down to the late February weak layer. A size 2 persistent slab avalanche was also noted on Sunday in the Dogtooth Range. The avalanche, which failed on a northeast aspect at 2200m, started as a smaller wind slab and stepped-down to the late February layer. This illustrates the touchy conditions in some areas. As stormy weather tapers-off and a dry ridge builds over the province, solar radiation will become the driver for natural avalanche activity.
Snowpack Summary
On lee features at treeline and in the alpine light amounts of new snow overlie older wind slabs while intermittent sunny skies have likely promoted a melt-freeze cycle on some sun-exposed slopes. 35-80 cm below the surface you'll find a persistent weak layer comprised of surface hoar, facets and/or a thick crust. This layer, which was buried on February 27th, seems variably reactive. In other words, it's still really touchy in some places while in other places it's really tough to trigger, and there's not much of a reliable pattern telling us what exact aspects are most suspect. I'd continue to be suspicious of steep, unsupported features at treeline and in the alpine as this layer has the potential for large avalanches. Deeper weak layers from mid-February and early January are now down 50-90cm and 70-120cm respectively. Triggering an avalanche on either of these layers has become unlikely but either still has the isolated potential to produce very large avalanches with a heavy trigger or significant warming. At ridgetop, cornices are huge and could be become increasingly touchy with forecast solar radiation.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.