Avalanche Forecast
Issued: Feb 23rd, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
ahanna,
Avalanche Canada
Fresh slabs sit on a layer of weak facets and bonding at this interface may take time. Ease into terrain cautiously and use low consequence test slopes to investigate.
In eastern areas that received less than 20 cm recently, avalanche danger is one step lower treeline and below.
Summary
Confidence
Weather Forecast
TUESDAY NIGHT: Clear, light northwest wind, freezing level valley bottom.
WEDNESDAY: Sunny, light northwest wind, freezing level 1000 m.
THURSDAY: Partly cloudy with scattered flurries, strong southwest overnight ridgetop wind easing to moderate, freezing level 1200 m.
FRIDAY: Mix of sun and cloud with scattered flurries, light westerly wind, freezing level 1000 m.
Avalanche Summary
Reports from near Golden include size 2 natural and explosive triggered storm slabs, as well as a size 1 skier remote reported in a MIN. One notable natural was reportedly triggered by a cornice fall.
Near Invermere, natural, explosive and skier triggered wind slab avalanches were size 1-1.5.
Earlier in February, there were a few reports of large avalanches (size 2.5-3) on southeast aspects in the alpine, likely releasing on a layer of facets on a crust (see a photo here), and a large human-triggered avalanche (size 2.5) on surface hoar near Quartz Creek.
Snowpack Summary
10 to 40 cm of new snow sits overtop of the old, faceted and/or wind affected snow that sat on the surface during the extended cold, windy drought period. At upper elevations, the new snow has been blown around by strong to extreme westerly winds, forming reactive slabs in lee features.
A weak layer that formed in late January is now 30-70 cm deep. In the northern Purcells this layer has been reported as a surface hoar layer at treeline and below treeline elevations, but a combination of facets on crusts could exist at all elevations throughout the region.
The northern Purcells also have an older surface hoar layer that can still be found 60-100 cm deep at treeline. Additional weak layers may exist near the bottom of the snowpack and steep rocky areas with a shallow or thin to thick snowpack should be considered suspect trigger points.
Terrain and Travel
- Choose slopes that are well supported and have limited consequence.
- Closely monitor how the new snow is bonding to the old surface.
- Be especially cautious as you transition into wind affected terrain.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Problems
Storm Slabs
10-30 cm of recent snow sits overtop of weak facets and/or extensively wind affected surfaces. Due to this weak interface, fresh slabs may be surprisingly sensitive to triggering. In the east of the region where less than 20 cm of snow fell, the problem is specific to wind loaded terrain features.
Cornices have likely experienced rapid growth with recent strong westerly winds. Fresh, unsupported tabs may weaken in the sun Wednesday. Tabs that break off can act as triggers on slopes below.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
There may be a lingering possibility of triggering persistent slab avalanches in isolated steep terrain features. The primary layer of concern is layer of surface hoar, facets, and/or crusts buried 40-80 cm deep throughout the region. Although we haven't received any reports of persistent slab activity in the most recent storm cycle, we don't believe that these limited results are conclusive enough to declare the problem gone.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 24th, 2021 4:00PM
