Avalanche Forecast

Issued: Mar 18th, 2017 7:00PM

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

Ruari Macfarlane, Parks Canada

Waterton Lakes.

Avoid steep sunny slopes, and exercise careful route-finding if you transition into Alpine terrain - Deep Persistent slabs are very hard to predict or assess, and the consequences of triggering such a deep avalanche would be nasty.

Summary

Weather Forecast

Sunday: Mainly sunny. Moderate Westerly winds. Freezing level at Valley Floor. Treeline Low -10, High -7.5Monday: Sunny. Light Easterly winds. Freezing Level 1400m. Treeline Low -10, High -6Tuesday: Increasing cloud. Flurries developing. Light-Moderate Southerly winds. Freezing Level rising to Treeline. Treeline Low -6, High 1.

Snowpack Summary

Around 30-40mm of rain on Saturday (less in the Eastern ranges) has saturated an already warm snowpack. A surface refreeze is expected by Friday morning. Strong SW winds are blowing new snowfall into Storm Slabs above 2100m. Deep Persistent layers will more sensitive than usual due to recent warmth, and the added weight of the new rain/snow.

Avalanche Summary

Several small Loose Wet avalanches and one Large (Size 2) Wet slab were observed Below Treeline on Saturday. It is expected more natural activity will be apparent on Sunday with better visibility.Three Large (Size 3) Deep Persistent slabs were observed during the past week (Most recent: Wednesday night), running from the Alpine to Valley Floor.

Confidence

Due to the number and quality of field observations

Problems

Storm Slabs

New snowfall with SW wind & warm temps has created fresh, reactive storm slabs on lee slopes. Expect these avalanches to be largest near the divide, including Cameron Lake area.

If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Avoid lee and cross-loaded terrain near ridge crests.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Deep Persistent Slabs

Recent warm temperatures & heavy snowfall has added stress to facets in the lower snowpack, and a crust in the mid snowpack that may have overlying facets in isolated areas. It will take days for temperatures to cool deep within the snowpack.

Avoid thin, rocky or sparsely-treed slopes.Minimize exposure to sun exposed slopes when the solar radiation is strong.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 4

Wet Slabs

The snowpack is waterlogged Below Treeline. Wet slabs remain a possibility for Sunday: water in the snowpack has pooled above several midpack crusts. These may act as failure plane. Dig to look for the ingredients: wet layers below a drier slab.

Minimize exposure to sun exposed slopes when the solar radiation is strong.Avoid slopes with glide cracks.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Mar 21st, 2017 4:00PM