Avalanche Forecast

Archived

Nov 24th, 2021–Nov 25th, 2021

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely.

Regions

South Coast.

Rapidly changing and dangerous avalanche conditions are on tap for Thursday. Thick storm slabs forming quickly and then getting pounded by rain is a great recipe for natural avalanche activity. It will be a good day to avoid avalanche terrain.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

Wednesday Night: Increasing flurries bringing about 15 cm of new snow. Moderate south winds.

Thursday: Increasing snowfall bringing 30-50 cm of new snow before transitioning to rain at all but high alpine elevations. Strong to extreme south winds. Treeline high temperatures climbing to around +1 with freezing levels reaching 2000 metres in the afternoon.

Friday: A mix of sun and cloud. Light west winds. Treeline high temperatures around -1 with freezing levels returning to 1200 metres.

Saturday: Cloudy with heavy rain; 30-50 mm. Light to moderate south winds. Treeline high temperatures around +5 with freezing levels rising to 3000 metres.

Avalanche Summary

No avalanches have been reported in the region. Forecast weather will shake things up on Thursday as heavy snowfall accumulates before temperatures warm enough for a transition to heavy rain at all elevations. Expect dramatic transitions from heavy snowfall forming reactive storm slabs to rain promoting wet loose avalanches over the day. Precipitation continues as temperatures cool overnight, so the storm should finish with dry snow. Rapid changes in precipitation rates and freezing levels throughout this event mean there is significant uncertainty around timing and transitions between avalanche problems as well as what problems may still exist on Friday.

Snowpack Summary

Thursday's storm is expected to bring 70-90 mm of precipitation to the region, however much of this will fall as rain, especially toward the closing hours of the event Thursday evening. At treeline it's reasonable to expect storm totals 30-50 cm before the rain switch. The highest alpine locations of the region could accumulate another 10-20 cm of new snow during this time.

The new snow and rain will land on generally wind-affected surfaces where snow cover exists. A hard rain crust is currently about 10 cm deep and another rain crust exists near the bottom of the snowpack. Average snow depths in the alpine are 100-120 cm. Snowpack depth tapers dramatically with elevation at treeline and below. Much of treeline and all below treeline elevations remain below threshold depths for avalanches.

Early season hazards such as rocks, stumps, and creeks are a concern below the alpine.

Terrain and Travel

The more the snow feels like a slurpy, the more likely loose wet avalanches will become.
The first few hours of rain will likely be the most dangerous period.
Minimize exposure during periods of heavy loading from rain.

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.

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.