Avalanche Forecast

Northwest Coastal

Date issued

Mar 21, 2018 - 4:36 PM

Valid until

Mar 22, 2018 - 2:00 PM

Prepared by

swerner

Storm slabs will build throughout the day. A MODERATE hazard may be the story in the am, but strong easterly winds and new snow is driving the danger to CONSIDERABLE in the alpine and at treeline by the afternoon.

Regular season
Wednesday - March 21, 2018
Alpine

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.

Treeline

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.

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

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.

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

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.

Avalanche Problem 1: Storm Slabs

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

The forecast storm snow will bond poorly to the plethora of old snow surfaces. It will likely step down deeper to the surface hoar layer buried March 9th. Uncertainty remains around the distribution of this layer.

Travel and Terrain Advice
  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Use caution in lee areas in the alpine and tree line, especially south / west facing slopes.

Avalanche Summary

No new avalanche reports on Wednesday.

The avalanche hazard will be on the rise with forecast rain, snow and strong winds.

Snowpack Summary

The snowpack consists of a wide variety of snow surfaces including pockets of wind slab, a melt-freeze crust on south-west aspects an wet snow down low, On March 9th, surface hoar and/or smaller facets (on sheltered, shady aspects) were buried by the last significant snowfall down 10-25 cm. The forecast storm snow over the next 2 days will likely have a poor bond to these older snow surfaces.

Deeper in the mid-pack, layers of crusts, facets, and isolated surface hoar buried 50 to 100 cm exist from mid- and late-February and a surface hoar/ crust layer from January is buried around 150 to 200 cm. Near the bottom of the snowpack, sugary facets exist in colder and dryer parts of the region, such as the far north.

Weather Forecast

Overnight Wednesday: 10-15 mm of precipitation amounts with moderate easterly winds. Freezing levels 1000 m and dropping to 600 m by the am.

Thursday: Snow amounts 10-15 cm with strong northeast-east winds. Freezing levels 500 m.

Friday: Cloudy with isolated flurries. Ridgetop winds light from the southwest. Alpine temperatures near -3 and freezing levels near 800 m.

Saturday: Mostly cloudy with some sunny periods. Snow amounts near 5 cm with ridgetop winds light/ gusting strong from the southwest. Freezing levels near 800 m.

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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