The sun packs a punch this time of year. If it shines you can expect the recent storm snow to become weak and reactive. Overhead hazards like cornices may fail and trigger large slab avalanches from the slope below.
Summary
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
A weak upper trough behind the current low will continue to bring unsettled conditions to the Interior. Localized periods of sunshine Thursday afternoon with prolonged sun on Friday.Thursday: Another 10 cm could arrive by the morning. Mostly cloudy skies with possible periods of sunshine in the afternoon. Alpine temperatures -6 and freezing levels 1400 m. Ridgetop winds L-NW. Friday: Mix of sun and cloud. Alpine temperatures near -4 and freezing levels near 1700 m. Ridgetop winds L-SW.Saturday: New snow 5-10 cm. Ridgetop winds M-SW and freezing levels 1700 m.
Avalanche Summary
On Tuesday, storm slabs proved to be reactive and ran naturally or easily triggered by the weight of a skier. Numerous avalanches were reported up to size 2. With continued precipitation, warming and wind, natural avalanche activity will likely continue on Thursday. Fragile cornices are also suspect which are a large enough to trigger deeper slabs to release on the slopes below. If you're traveling below treeline where the avalanche hazard may be lower than it is in the alpine you still need to be diligent with your terrain use and focus on potential overhead hazards by avoiding lingering in run-out zones where large avalanches to come from above.
Check out the recent Forecaster Blogs for more details.Snowpack Summary
Up to 30 cm of recent storm snow has accumulated at upper elevations and is reactive. This now brings 30-70 cm of accumulated snow over the past week which overlies a rain crust below 2000 m or a sun crust on solar aspects at higher elevations. New wind slabs are developing on leeward slopes and behind terrain features and large, fragile cornices exist along ridgelines. At lower elevations, there may be multiple crust layers in the upper snowpack which are now generally well bonded. At higher elevations, the February weak layers are down 120-150 cm and woke up during last week's storm with many avalanches stepping down to them. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches and cornice falls have also stepped down to these layers last week resulting in some very large full depth avalanches.
swerner,
Avalanche Canada
