Cornices and daytime heating are the two big concerns today. Watch for changing conditions throughout the day, and with changes in elevation and aspect.
Weather Forecast
A weak ridge will remain over the area today bringing mostly sunny skies. The sun is expected to "pack a punch" today - i.e. strong solar radiation and heating. We had little overnight recovery in temperatures, so the snow can be expected to get moist earlier in the day. Another small disturbance will move through on Thursday.
Snowpack Summary
The generally well settled snowpack is being affected by strong solar radiation. North aspects are remaining cool, but sunny aspects and all lower elevations are warming up substantially during the day. Thin snowpack areas will be most susceptible, specifically on S and W aspects. Several PWLs (mostly buried sun crusts with SH) are still active.
Avalanche Summary
More very large avalanches were observed in the Selkirks yesterday. Most of these were triggered by cornice failures. Near Glacier Park, a size 4.5 slab was reported, triggered by a cornice fall. Cornice triggered avalanches have increased throughout the area, with warm daytime temperatures. Moist avalanches were noted at lower elevations.
Problems
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.
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.