Regions
Northwest Coastal.
A storm crashes into the NW Coast Friday forcing the freezing level down to about 1000m and is expected to generate significant snowfall through the weekend. Approach the mountains as if the calendar says January, not April.
Weather Forecast
Cloud developing overnight. Light snow and strong southwest winds by Friday morning with freezing levels at 1000 m. Strong southwest winds on Friday with 10 to 15 cm of new snow above 1000 m in near coastal areas of the region. Another 10 to 15 cm is expected on Saturday with strong southerly winds and freezing level at 1500 m. More snow on Sunday, 15 to 20 cm expected overnight and during the day with strong southerly winds. This storm is coming from the south and may not push very far inland as a blocking ridge steers the moisture towards the north.
Avalanche Summary
On Wednesday loose wet avalanches were reportedly running naturally to size 1 on north through west facing terrain between 1300 and 1600 m. On Tuesday loose wet/"moist" avalanches to size 2 were observed from steep rocky terrain. On both Sunday and Monday, loose wet avalanches up to size 2.5 were reported in the far north of the region. With the arrival of spring, field observations and data have become quite limited in the region.
Snowpack Summary
5 to 20 cm of new storm snow has fallen at higher elevations in the last 48 hours. Strong winds have generally been out of the south, but some wrap around east/southeast winds have also been reported. These winds have redistributed the recent storm snow in exposed alpine terrain and likely formed wind slabs in leeward features. The new snow has buried a widespread melt-freeze crust. With the exception of high elevation shaded terrain, the region likely returned to melt-freeze conditions on Wednesday allowing the surface to melt during the day resulting in crust formation overnight. The snowpack's strength is directly related to the thickness and strength of these surface crusts. A widespread crust/facet layer from early February and depth hoar at the bottom of the snowpack (primarily in northern & inland areas) are dormant. Cycles of melting and refreezing have limited the reactivity of these old layers. However these layers, or the ground, could potentially be the layer for an isolated yet large avalanche with prolonged periods of warming.
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.