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Avalanche Forecast

Archived

Mar 22nd, 2017–Mar 23rd, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

North Columbia.

Thursday's danger will be driven by the amount of sun you get in your local area. When the sun is out in full strength, expect natural avalanches including the potential for large persistent slabs. Conservative terrain selection remains critical.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Thursday

Weather Forecast

Another 5-15 cm of snow is expected Wednesday overnight with strong alpine wind from the southwest and freezing levels at 1200-1500 m. A mix of sun and cloud is expected on Thursday with moderate alpine wind from the southwest and freezing levels reaching around 1500 m in the afternoon. 4-8 cm of snowfall is forecast for Friday with moderate southwest wind in the alpine and freezing levels reaching 1500 m or so in the afternoon. Similar conditions are forecast for Saturday with light snowfall, moderate alpine wind, and freezing levels reaching around 1500 m in the afternoon.

Avalanche Summary

On Tuesday, a natural cornice release triggered a size 1.5 storm slab on a northwest aspect at 2050 m elevation. Skiers triggered a size 1 wind slab on a west aspect at 2100 m and a size 1 storm slab at 2000 m. These were 20-25 cm thick. On Monday, a natural cornice release triggered a size 3.5 deep persistent slab on a north aspect at 2500 m released on glacier ice and ran to valley bottom. Several other large natural cornice releases and storm slabs avalanches were reported, with a few stepping down to deeper layers. Over the weekend, a widespread avalanche cycle occurred with avalanches up to size 4.5. This included very large cornice releases, avalanches releasing on layers near the base of the snowpack, propagations over 1 km wide, and mature timber being broken. Click here for photos of the recent avalanches.On Thursday, sun is expected to drive the hazard. If there is are long periods of strong sun, expect sluffing from steep sun exposed slopes, cornices will become weak, and persistent slab avalanches could fail naturally. With the recent avalanche activity and several weak layers within snowpack waking up, it is a time to be very conservative with terrain selection.

Snowpack Summary

15-25 cm of new snow typically overlies the thick rain crust which formed over the weekend. The crust has been reported up to around 2000 m and has been reported to be supportive to skiers between 1500 and 1900 m. Alpine wind has recently been strong from a variety of directions and has formed wind slabs on all aspects. Large cornices are also reported on northerly aspects in the alpine. The rain crust which formed last week is now down 40-60 cm and generally seems to be well bonded to the surrounding snow. The February weak layers are down 100-150 cm and woke up during the recent storm cycle with many avalanches stepping down. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches stepping down to these layer recently resulting in very large avalanches.

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.

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.

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.