Regions
Northwest Coastal.
Touchy and dangerous conditions still exist in many parts of the region. Continued warm, wet and windy conditions will keep the Avalanche Danger HIGH.
Confidence
Moderate - Freezing levels are uncertain on Wednesday
Weather Forecast
Warm, wet and windy conditions will persist for Wednesday and Wednesday night. Expect between 20-30mm of precipitation, extreme southerly winds and freezing levels at about 1700m. On Thursday, the region should see between 15-20cm of snow, strong southwest winds and freezing levels dropping to about 1200m. By Friday, a pattern shift should bring light flurries, light winds and freezing levels closer to 1000m.
Avalanche Summary
Explosives control over the weekend produced numerous slab avalanches up to size 3.5. Most of these failed on the mid-January surface hoar and some stepped down to the Boxing Day surface hoar layer. One observer also viewed numerous size 3 natural slabs on a variety of aspects, but these may have been a day or two old. With the current wet and stormy conditions observations will be limited, but we can expect new storm slab activity at elevations where precipitation falls as snow. More importantly, precipitation will add stress to buried persistent weak layers and will increase the likelihood of destructive persistent slab avalanches.
Snowpack Summary
A warm, wet and windy storm is forming dense new storm slabs at higher elevations while rain is saturating surfaces at lower elevations. The January 9th surface hoar/facet layer is down 60-100 cm in most places, and seems most concerning at and below treeline. Approximately 10 cm below this weakness you might find the Dec. 26/31 surface hoar layer. Ongoing reports of remote triggering, whumpfing, and sudden shears in snowpack tests are all indications that these layers are touchy and could propagate well if triggered. Deeper persistent weaknesses buried in December have the potential to wake-up to heavy loading, rapid warming, or avalanches stepping-down.
Problems
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.
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.