Avalanche Forecast

Issued: Mar 4th, 2014 8:41AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Storm Slabs and Persistent Slabs.

rbuhler, Avalanche Canada

South Rockies.

In localized areas with deeper storm snow accumulations or wind loading, the danger rating may be HIGH on Wednesday. Watch for local signs of instability.

Summary

Confidence

Poor - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Snow or rain is expected for Wednesday and Thursday but amounts are uncertain. Freezing levels should rise to around 2000m. Dry conditions are expected for Friday with some clearing. Wednesday: Rain or snow 10-20mm, freezing level around 2000m, ridgetop winds 30-50 km/h SWWed. Night/Thursday: Rain or snow 10-20mm, freezing level 1000-1500m, ridgetop winds 40-60 km/h SWFriday: A mix of sun and cloud, mainly dry conditions, freezing level around 2000m, ridgetop winds 20-40 km/h SW-NW

Avalanche Summary

On Tuesday, we received a report of a natural storm slab avalanche and multiple human-triggered storm slab avalanches up to size 2 releasing down as deep as 35cm.

Snowpack Summary

20-40cm of new snowfall overlies surface hoar, facets, and/or a sun crust on south aspects. Recent moderate to strong SW winds have created wind slabs in leeward and cross-loaded features. The primary concern remains a persistent slab that sits on a stubborn persistent weak layer consisting of a crust, facets, and/or surface hoar. The layer continues to show a high degree of sensitivity to human triggers but is becoming more isolated. In the thinner snowpack areas such as the Crowsnest and northern Elk Valley, the slab is typically 30-60cm thick (below new snow). In thicker areas such as the Flathead and around Fernie, the slab typically varies in thickness from 70-150cm. Check out the South Rockies Blog for a video discussing the persistent weak layer and the current avalanche problem. A weakness at the base of the snowpack may still exist in isolated areas of the region but triggering has become unlikely.

Problems

Storm Slabs

Accumulating storm snow is sitting on a weak layer of facets, surface hoar, and/or a sun crust. Strong SW wind has created stiffer wind slabs in leeward features.

Avoid freshly wind loaded features.>The new snow will require several days to settle and stabilize.>Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

The deeply buried persistent weak layer still has the potential to produce large and destructive avalanches. Isolated slopes are still primed for human triggering and remain a concern on all aspects and elevations.

Avoid unsupported slopes.>Use conservative route selection, resist venturing out into complex terrain even if you observe no obvious signs of unstable snow.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

3 - 6

Valid until: Mar 5th, 2014 2:00PM