Avalanche Forecast
Issued: Mar 1st, 2020 5:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
astclair,
Avalanche Canada
Incremental snow and wind over a buried weak layer warrants careful evaluation and terrain selection on Monday.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Sunday night: Cloudy, isolated flurries with trace accumulations, moderate west winds, gusting strong at ridge-top, freezing level 500 m.Â
Monday: Cloudy, up to 5 cm of snow, moderate west winds, gusting strong at ridge-top, freezing level 1100 m.
Tuesday: Mostly cloudy, 5-10 cm of snow, moderate southwest winds, gusting strong at ridge-top, freezing level rising to 1300 m.Â
Wednesday: Decreasing cloud, 10-20 cm of snow overnight, moderate southwest winds decreasing to light, freezing level 900 m.
Avalanche Summary
In the aftermath of the storm, observers reported a natural avalanche cycle of small to large (size 1-2.5) slab avalanches releasing in the recent snow 20-40 cm deep. Some of this avalanche activity was human triggered (see this MIN for a helpful example). Explosive mitigation on Saturday also triggered several large cornices. Periods of strong solar radiation Saturday afternoon initiated pinwheels, rollerballs, and small wet loose avalanches on steep, sunny slopes.
On Wednesday, a large (size 2) human-triggered avalanche releasing on the February 22 surface hoar was reported. Â
Snowpack Summary
20-30 cm of snow has accumulated since Friday. Strong winds redistributed the storm snow into reactive wind slabs on lee features at upper elevations and rapidly loaded cornices.Â
Buried 50-80 cm deep, a weak layer of sugary faceted snow and feathery surface hoar from February 22 may persist and warrants careful evaluation. Operators observed recent reactivity in snowpack tests and reported whumpfing in terrain near Tricouni. Check out the latest forecaster blog that offers a deeper dive into these conditions.
Faceted snow and crusts exist near the base of the snowpack in much of the region. This layer is has been dormant recently.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
Problems
Wind Slabs
20-30 cm of recent snow and strong westerly winds have formed wind slabs on leeward terrain features at upper elevations that may remain possible to human trigger. These areas of concern overlap with where cornices may also be reaching their breaking point.
Aspects: North, North East, East, South East, South, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
40-70 cm cm of snow is settling over a layer of surface hoar on sheltered slopes near and above treeline. Recent snow and wind have promoted cohesion in the slab above, priming it for human triggering. Travelling near steep, open slopes at upper elevations warrants an investigation of this deeper layer.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 2nd, 2020 4:00PM
