Avalanche danger ratings in the alpine on Sunday and Monday are HIGH where direct sunshine is affecting the slope. If it's cloudy, assume the danger is CONSIDERABLE.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
Sunday: Locally variable light convective snow showers, amounting to a few cm. Sunny breaks in the afternoon. Generally light winds. Freezing level near 600m.Monday: Scattered cloud. Light winds. Cool in the morning and warming by afternoon with the influence of sunshine. Freezing level near 600m.Tuesday: Moderate snow and moderate to strong south-westerly winds. Freezing level between 500m and 1000m.
Avalanche Summary
On Thursday, a natural loose moist avalanche cycle was observed in the Coquihalla region between 1400-1700m, with avalanches of size 2-3.5. A few slabs also released, with crowns of 50-60 cm. Explosives testing in the Duffey Lake area produced slab avalanches up to size 2.5 and skiers triggered very touchy storm slabs to size 1.5. The recent storm snow may become reactive under the influence of direct sunshine on Sunday or Monday. Surface avalanches could step down to deeper weak layers, creating large avalanches.
Snowpack Summary
Recent storm snow has created slabs at all elevations, which started out being very touchy, but seem to have gained strength. Strong southerly winds have created wind slabs behind ridgelines and terrain breaks. Crusts down 50-60 cm can be found on solar aspects in the Duffey Lake, Chilcotin, and Coquihalla areas. These exhibit moderate to hard, sudden results in snowpack tests. Deeper persistent weak layers are variable in distribution across the region. A crust/surface hoar/facet layer buried in early February, now down about 1.5m, is still is a key concern. It is especially prevalent on south-facing slopes above treeline, and all slopes below treeline. Although the likelihood of triggering this layer has decreased, the potential for surprisingly large avalanches remains.
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.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.