Regions
Northwest Coastal.
Confidence
Fair - Due to variable snowpack conditions
Weather Forecast
Wednesday: Expect mostly cloudy skies with a chance of flurries. Winds should be light southerly and alpine temperatures should reach -6.Thursday: We should see a mix of sun and cloud with winds turning westerly then northwesterly and strengthening. Alpine temperatures should again reach around -6.Friday: Clouds return with a slight chance of flurries. Winds settle back to westerly and increase to moderate/strong values. Expect temperatures around -6.
Avalanche Summary
The region has seen a natural avalanche cycle. Natural slabs and cornice falls up to size 3.0 have been reported, predominantly on north-northeasterly terrain. Many loose wet avalanches up to size 2.0 have occurred below treeline, where the recent precipitation fell as rain. Both explosive and rider controlled avalanches have also been observed up to size 2.5, predominantly in wind loaded areas. Some areas are reporting reverse loading from changing wind directions and have seen windslab failures in southeast facing terrain features.
Snowpack Summary
The recent storm has past, bringing cooler temperatures and a lull in precipitation. The storm snow is settling very quickly. Below 1000m, much of the precipitation fell as rain and the low elevation snowpack remains moist below the recently formed crust.The tail of the storm brought strong southwest winds, giving intense snow transport and cornice growth. Extensive windslabbing in lee zones and behind ridges in the alpine and treeline was the result. Large cornice failures are possible. Some areas saw swirling winds resulting in some cross and reverse loading on southeasterly features.In the upper snowpack, a thin melt-freeze crust buried on Jan. 17 and a persistent weakness of surface hoar and/or facets remain a concern. I'm thinking the new storm load will accelerate the bonding process and put these layers to bed, but its worth keeping them on your radar in regards to distribution and reactivity for the short term. The mid and lower snowpack is generally well settled and strong, but basal facets remain a concern in the northern part of the region.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.