Regions
Northwest Coastal.
Recent winds have been highly variable, and so is the reactivity of recent storm snow. Make observations continually as you travel.
Confidence
Moderate - Wind effect is extremely variable on Wednesday
Weather Forecast
The current ridge of high pressure will deliver clear skies for Wednesday and Thursday while increased cloud is expected on Friday. An inversion will develop over the forecast period with above-freezing alpine temperatures expected by late Thursday and Friday. Ridgetop winds should be light and northeasterly on Wednesday increasing to strong and southwesterly on Thursday and Friday
Avalanche Summary
Evidence of natural storm slab avalanches to size 2 was observed in the wake of Saturday's storm. Natural avalanche storm slab activity has tapered-off with the current clearing trend. However, human-triggered avalanches will remain a concern for the forecast period, especially at elevations or in parts of the region where recent storm accumulations have settled into a cohesive slab. Small solar-induced loose wet avalanches have also been reported. The likelihood and size of loose wet avalanches will increase with warmer alpine temperatures expected during the forecast period.
Snowpack Summary
Last weekend, between 25cm and 40cm of new snow fell. Wind speed and direction during, and since, the storm have been highly variable. In areas where the wind was strong, there may be a cohesive and reactive storm slab. In areas where the winds were light, you're more likely to find loose powder. The recent storm snow overlies a touchy layer of loose facets and well-developed surface hoar which is reported to exist on most aspects and elevations. Due to the persistent nature of these underlying crystals, newly formed storm slabs may remain reactive for some time. Solar radiation has also come into play, and depending on the time of day, steep solar aspects may be moist or refrozen.Professionals in the region are still keeping an eye on a few other surface hoar layers that developed throughout December which are now buried in the top 100cm. Although these layers may be gaining some strength, they are worth investigating, especially in steep, unsupported terrain.
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.
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.