Regions
Northwest Inland.
Weather Forecast
A series of Pacific frontal waves and upper troughs will bring continued unsettled weather through the forecast period. Light -moderate precipitation amounts can be expected daily. With fast moving systems, timing seems to be hard to pinpoint. A strong upper SW flow will provide warmer the normal temperatures, rising freezing levels in the afternoon, then falling during the night. Things should start to cool off significantly by Friday. Wednesday: Snow amounts 5-10 cm. Ridgetop winds moderate from the South. Freezing levels 900-1000 m. Thursday/Friday: Light precipitation both days. Ridgetop winds mod-strong from the SW. Freezing levels 900 m, falling to valley bottom. on Friday.
Avalanche Summary
On Monday, 1 natural cornice failure triggered a slab avalanche size 2 on the slope below. This was on a NE aspect around 1300 m. Other operations have reported no new avalanche activity through their tenures.
Snowpack Summary
Moderate southerly winds have formed wind slabs in the alpine, and at treeline on lee and cross-loaded terrain. North aspects at higher elevations hold dryer, low density snow in the upper 20 cm. Spring-like conditions exist and crusts have formed on solar aspects at all elevations, becoming moist under sunny skies. Melt-freeze conditions exist below treeline on all aspects. Below this sits a well consolidated, settled mid pack. The mid February persistent weak layer, comprised of spotty surface hoar, facets and crusts, is buried 80-120 cm below the surface. No recent activity has been reported on this interface, although I feel that triggering may be possible in steep, isolated terrain in some parts of the region. If an avalanche occurs on this weak interface it will be very large and destructive. Below this the snowpack is well settled and strong. Cornices in the area are reported to be very large. Cornice failure could trigger an avalanche on the slope below.
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.
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.
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.