Regions
Northwest Coastal.
We have just come out a significant loading period, with lots of variety throughout the region. Although the DANGER trend is decreasing, a conservative approach is recommended through the forecast period.
Confidence
Fair - Due to variable snowpack conditions
Weather Forecast
Tuesday: Expect cloudy skies with a chance of flurries, light southwesterly winds and alpine temperatures reaching -7.Wednesday & Thursday: Light flurries linger with continued cloudy conditions. Light southerly winds persist with alpine temperatures reaching -7 each afternoon.
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, predominantly in wind loaded areas.
Snowpack Summary
The recent storm has past, bringing cooler temperatures and a lull in precipitation. In some areas, as much as 75-100cm of new snow fell. Below 1000m, much of the precipitation fell as rain. 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 will be the result, and large cornice failures are inevitable.At lower elevations the snow in moist as deep as 50cm. The cooling temperatures will have created a strong crust on the surface, but the weak, wet snow will take some time to settle and bond. A thin melt-freeze crust buried on Jan. 17 may prolong this issue.Lingering deeper sits a persistent weakness comprising of surface hoar and/or facets. Recent tests on this layer are showing both sudden and resistant planar results. We have also seen an extended column test at 30/100 (end) indicating the propensity for propagation if this layer were triggered. Keep these layers on your radar in regards to distribution and reactivity. The mid and lower snowpack is generally well settled and strong, 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.