Avalanche Forecast

Archived

Jan 30th, 2020–Jan 31st, 2020

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural and human triggered avalanches likely.

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.

Regions

Kootenay Boundary.

Avalanche danger will increase through the day Friday. In areas where new snow depths exceed 30 cm, avalanche danger will rise to HIGH in the alpine. At lower elevations the potential for loose wet avalanches will increase as the upper snowpack becomes soaked by rain.

Confidence

High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

Thursday night: 5-10 cm new snow, rain below 1000 m. Moderate to strong southwest wind. Freezing level rising to 1200 m.

Friday: 10-20 cm new snow turning to rain below 1800 m. Strong southwest winds. Freezing level rising to 2100 m.

Saturday: 10-20 cm new snow with rain below 1800 m turning to snow as freezing levels drop. Strong southwest winds, extreme at ridgetop. Freezing level 2000 m dropping to valley bottom by Sunday morning.

Sunday: Sunny. Light northwest wind. Alpine high -4 C. Freezing level valley bottom.

Avalanche Summary

On Sunday through Wednesday, storm slabs were reactive to skier traffic, producing avalanches up to size 1.5 on north to east aspects in the alpine.

Reports of deep persistent avalanches have been periodically coming in from the western boundary area over the past few weeks. On Tuesday, explosive work released a cornice which triggered a deep persistent slab over 2 m deep in a chute below. On Monday, two deep persistent slab avalanches were reported in shallow snowpack areas on southwest aspects around 2000 m, with crown depths of 1 m or greater. A size 1.5 was vehicle triggered above a cut bank. A size 2.5 was remotely triggered by a skier in a thin to thick snowpack area. The new loading from snow and rain will further stress these buried weak layers.

Snowpack Summary

15-30 cm of heavy new snow in the alpine is being loaded into lee features by strong southwest wind. Below 1800 m, the upper snowpack is becoming soaked by rain.

A layer of surface hoar is buried 100-150 cm below the surface in sheltered areas around treeline but has not been associated with avalanche activity recently. Weak basal facet/crust layers are particularly noteworthy in the western Boundary area. The few recent avalanches associated with this problem have been triggered either by very large loads or from shallow, rocky snowpack areas.

Terrain and Travel

Minimize exposure during periods of heavy loading from new snow, wind or rain.
Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
Be aware that wet activity at low elevations is a classic situation for step-down failures in deeply buried persistent weak layers.

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.