Avalanche Forecast

Issued: Mar 19th, 2016 4:00PM

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

Tim Haggarty, Parks Canada

Banff Yoho Kootenay.

Watch for warming to increase the potential for skier triggered and natural loose wet avalanches. With the potential for triggering the persistent and deep persistent layers be conservative with your exposure to avalanche terrain through Monday.

Summary

Weather Forecast

Despite mainly clear skies Saturday, light winds prevented freezing levels from breaking treeline. We expect freezing levels to reach treeline by mid day Sunday and stay there as a warm SW flow brings moist air. Light precip (rain?) is expected with a poor overnight recovery as winds shift to West and increase to moderate at treeline into Monday.

Snowpack Summary

The snowpack is complex right now. Suncrusts now cap the 40-100 cm of snow which sits on deeper crusts on W through E aspects right up to alpine elevations. These slabs have been reactive with explosives in many areas recently. Thinner snowpack areas have prominent facets at or near the base. Large cornices are sitting above many lee slopes.

Avalanche Summary

Avalanche control on Mts. Stephen ad Dennis Friday produced avalanches to size 3. On the same flight numerous large natural avalanches to size 3 were observed. These were 24-48 hours old on NE through N aspects in the alpine, some stepping right to ground or near ground.

Confidence

Freezing levels are uncertain on Sunday

Problems

Loose Wet

A mild inversion Sunday with a chance of rain and a poor recovery into Monday could cause surface events. These could provide enough mass to trigger persistent and deep persistent weak layers (listed below) causing larger avalanches.

Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.Watch for clues, like sluffing off of cliffs, that the snowpack is warming up.

Aspects: North, North East, East, South East, South.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

Avalanches on buried crusts with facets have been seen on solar aspects within the last few days. Presently there are several crusts buried with 40-100 cm overlying them.

Dig down to find and test weak layers before committing to a line.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Deep Persistent Slabs

Deeper facet layers remain weak, especially in thin or rocky areas. Avoid steep or unsupported terrain and be very conservative with large terrain features. A great deal of variability exists. Dig a lot of holes and use your probe to get information

Avoid steep convexities or areas with a thin or variable snowpack.Watch for signs of instability such as whumpfing, or cracking.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Mar 20th, 2016 4:00PM