Avalanche Forecast

Archived

Jan 31st, 2020–Feb 1st, 2020

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural and human triggered avalanches likely.

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 unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Lizard-Flathead.

Heavy snow and warm temperatures are expected on Saturday which will result in dangerous avalanche conditions. Travel in avalanche terrain is not recommended.

Confidence

High - We are confident the snowpack will rapidly lose strength with the arrival of the forecast weather.

Weather Forecast

Friday night: around 10 cm new snow at high elevations, rain lower down. Strong southwest winds. Freezing level around 1900 m.

Saturday: 15-25 cm new snow, rain at lower elevations. Strong to extreme southwest winds. Freezing level around 1700 m.

Sunday: Dry and sunny. Light northwesterly winds. Freezing level around 500 m.

Monday: Dry with sunny breaks. Light notheasterly winds. Freezing level at surface with alpine temperatures around -10C.

Avalanche Summary

On Thursday, a number of natural wind slab avalanches were observed up to size 2.

With anticipated new snow and rising temperatures, avalanches will become much more likely on Saturday.

Snowpack Summary

Recent storm snow combined with southwest winds have producing slabs in the alpine and exposed tree line areas. Cornices have been noted along ridgelines. The recent snow covers a temperature crust which formed up to around 1600 m.

The upper snowpack continues to settle in mild temperatures. Several crust layers exist in the mid-pack as a result of previous warming and rain events. These have not been identified as bed surfaces or failure planes in recent avalanche activity. The bottom 10-20 cm of the snowpack consists of faceted snow and decomposing crusts. Although this basal layer has not been an active avalanche problem in the region since December, if there's anything that will wake it up again, it's a warm, moist storm, such as the one forecast for Saturday.

Terrain and Travel

Avoid all avalanche terrain during periods of heavy snowfall.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.