Avalanche Forecast

Issued: Mar 8th, 2017 5:38PM

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

Ruari Macfarlane, Parks Canada

Waterton Lakes.

Heavy snowfall on Friday will be accompanied by warming temperatures and Strong Westerly winds - prime material for slab building! If new snowfall amounts over Thursday/Friday exceed 35cm, consider danger HIGH at Treeline.

Summary

Weather Forecast

Two airmasses collide - snowfall amounts are tricky to predict.Thursday: Snow overnight (5-10cm), easing. Temperature inversion. Light SW winds.Friday: Snowfall, heavy in the West (20-45cm). Freezing level rising. Treeline High: -5. Winds rising to Strong W. Saturday: Sun & cloud, light snowfall later. Moderate SW winds. Treeline High -5

Snowpack Summary

Snow has fallen daily since February 25. Deep, low-density snow is forming Storm Slabs lee to SW winds above 1800m, where warm winds are riding over cold Arctic air in the valleys. The old snow surface from Jan 25 (small facets) is down 70-90cm. This layer may be reactive where it sits on a crust (Solar aspects, primarily at Treeline).

Avalanche Summary

Early in the week, a Large Cornice fall at Treeline triggered a slab in steep, lee terrain, resulting in a Large (size 2.5) avalanche. On Tuesday, forecasters easily ski cut Small (Size 1) Loose Dry avalanches in steep terrain. On Wednesday, Several Natural Storm Slabs (Size 1.5) were observed from NE-NW aspects at Treeline.

Confidence

Forecast snowfall amounts are uncertain on Friday

Problems

Storm Slabs

Storm Slabs exist on Thursday, but will grow in size and sensitivity on Friday, and will remain primed for human triggering on Saturday. Pay special attention to slopes lee to SW winds - these winds will build touchy slabs on lee slopes.

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: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 3

Loose Dry

These will be a problem in areas sheltered from the wind, especially in confined features like gullys. The problem will grow in proportion to new snow amounts.

Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.Choose ice climbs that are not exposed to avalanches from above.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

There is uncertainty about the distribution of this layer, it is suspected to be most reactive at Treeline, on steep S and SW aspects where facets overlie a crust.

Whumpfing, shooting cracks and recent avalanches are all strong inicators of unstable snowpack.Carefully evaluate terrain features by digging and testing on adjacent, safe slopes.

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Unlikely

Expected Size

1 - 3

Valid until: Mar 11th, 2017 4:00PM