Avalanche Forecast

Kootenay Boundary

Date issued

Mar 21, 2018 - 4:37 PM

Valid until

Mar 22, 2018 - 2:00 PM

Prepared by

ghelgeson

Thursday's storm snow is not expected to bond well to the old surface. Watch for increasing hazard throughout the day and be aware that there may be pockets of considerable hazard, especially in wind loaded terrain late in the day.

Regular season
Wednesday - March 21, 2018
Alpine

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Thursday - March 22, 2018
Alpine

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Friday - March 23, 2018
Alpine

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Avalanche Problem 1: Storm Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

New snow is not expected to bond well to the old surface which is a mix of crusts, surface hoar and facets. Natural and human triggered avalanches are anticipated as storm snow accumulates throughout the day.

Travel and Terrain Advice
  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Storm slabs are expected to most sensitive to triggering in wind exposed terrain.

Avalanche Summary

No significant avalanche observations to report from the last few days. New snow and wind Thursday are expected to initiate natural avalanche activity.

Snowpack Summary

New snow Thursday will fall on a slippery crust that is present at all elevations on solar aspects. Low elevation polar aspects also have a crust, but treeline and alpine elevations feature a mix of large surface hoar and surface facets.

About 5 cm of snow is between the surface and another interface that mirrors the surface; crust on solar, surface hoar on high elevation north.

Snow that fell March 8th/9th was redistributed by west/southwest wind, forming wind slabs at high elevations. These wind slabs rest on a layer of surface surface hoar about 25 to 40 cm below the surface which has not been recently reactive.

A mix of weak layers exist 50 to 100 cm below the surface, including small surface hoar on shady aspects and a crust on solar aspects. These layers are expected to have gained strength from recent cycles of warming and cooling. Like other deeper weak layers that formed in January and December, they are considered dormant at this time. These deeper layers include several surface hoar and facet layers 1 to 2 m below the surface and a crust/ facet interface near the base of the snowpack.

Weather Forecast

A rather complex pattern is expected to deliver a significant shot of precipitation and wind with a warm to cold trend. This storm should be most intense Thursday and begin to clear a bit as we enter the weekend. This is a great time to check out the Mountain Weather Forecast for further details! (Link below)

WEDNESDAY NIGHT: Freezing level around 1800 m, strong southerly wind, about 1 to 5 mm of precipitation.

THURSDAY: Overcast, freezing level holding near 1800 m all day, moderate to strong south/southeast wind, 8 to 15 mm of precipitation expected.

FRIDAY: Broken cloud cover, freezing level beginning around 600 m rising to 1400 m, moderate to strong southwest wind, 1 to 5 mm of precipitation possible.

SATURDAY: Broken cloud cover, freezing level beginning around 400 m rising to 1400 m, moderate to strong southwest wind, 2 to 6 mm of precipitation possible.

Danger Ratings Explained

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Natural avalanches possible; human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

4 - High

Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Natural avalanches likely; human-triggered avalanches very likely.

Large avalanches in many areas; or very large avalanches in specific areas.

5 - Extreme

Avoid all avalanche terrain.

Natural and human-triggered avalanches certain.

Large to very large avalanches in many areas.

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