Avalanche Forecast

Fair - Timing or intensity of solar radiation is uncertain

An unstable air mass will bring mainly cloudy skies and light snow amounts through the weekend, with freezing levels remaining at or near the valley bottom. If the sun shines through, solar radiation will be strong. Saturday: Snow amounts 5-10 cm. Ridgetop winds light gusting moderate from the South. Alpine temperatures near -5. Freezing levels 1000 m. Sunday: Overcast with light snow amounts in the morning. Winds will generally be light, gusting moderate from the South. Freezing levels at valley bottom. Monday: A weak ridge of high pressure will bring dry, cooling conditions and light Southerly winds. Sunshine should prevail through the day, solar radiation may be strong.

Thursday the Coquihalla saw a widespread natural wet avalanche cycle between 1400-1700 m. Most slides were point releases, entraining mass from the recent storm snow, up to size 3.5. A few avalanches were slabs with crown depths down 50-60 cm. This cycle occurred on all aspects, with no step down releases on lower weak layers. Explosive testing done on the Duffy produced slab avalanches up to size 2.5. On Wednesday natural sluffing from steep terrain, and skier triggered pockets at treeline and below were reported. I suspect more natural activity occurring in the alpine with the new snow and cranking SW winds. Last week, warming prompted a widespread natural cycle in the Coquihalla and skiers triggered very touchy persistent slabs at low elevations. An unnervingly large natural avalanche cycle occurred at the start of this month, with slabs up to size 4.5 propagating 2-3km along ridgelines and stepping down to the mid-February layers. With possible sunny breaks this weekend, I suspect the new storm snow could become reactive under the influence of solar radiation. It's possible that solar induced avalanches could step down to deeper weak layers, creating large avalanches.

Recently, 30-50 cm of new storm snow has fallen over the region, building storm slab at all elevations. Strong southerly winds have created wind slabs lee of ridgelines and terrain features. Crusts down 50-60 cm can be found on solar aspects in the Duffey Lake, Chilcotin, and Coquihalla areas. Previously, these crusts had a poor bond. Tests done on these crusts are showing moderate-hard results with sudden planar characteristics. With the additional stress of a new load, these crusts may act as a sliding layer. Storm and wind slabs could overload these crusts, or even deeper the persistent weak layers(surface hoar, facets, crusts). Persistent weak layers are variable in distribution across the region. Generally they exist down 150 cm. Recent testing produced whumpfs and sudden planar results in snowpack tests. It is still is a key concern for step-down avalanches in many parts of the region. It is especially prevalent on south-facing slopes above treeline, and all slopes below treeline. Very large avalanches are possible, which could be remote-triggered, triggered mid-slope, and/or propagate into low-angled terrain.