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Avalanche Forecast

Archived

Mar 29th, 2017–Mar 30th, 2017

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Columbia.

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.

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.

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.