Avalanche Forecast

Northwest Coastal

Date issued

Mar 17, 2018 - 3:53 PM

Valid until

Mar 18, 2018 - 2:00 PM

Prepared by

mgrist

Expect to find lingering wind slabs at high elevations and wet snow at low elevations, especially if the sun comes out for any length of time.

Regular season
Sunday - March 18, 2018
Alpine

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.

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.

Monday - March 19, 2018
Alpine

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.

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.

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.

Tuesday - March 20, 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

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.

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: Wind Slabs

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

Isolated wind slabs may linger in lee features. These slabs overly a weak surface hoar layer in parts of the region, which have produced wide propagations and fast-moving avalanches.

Travel and Terrain Advice
  • Approach lee and cross-loaded slopes with caution.
  • Avoid steep, rocky, and wind affected areas where triggering slabs is more likely.

Avalanche Problem 2: Loose Wet

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

Mid-mountain freezing levels (and a possible lack of overnight re-freeze) will mean that loose wet avalanches are more likely at lower elevations. Use caution in terrain features where a small avalanche could have serious consequences.

Travel and Terrain Advice
  • Watch for signs that the snow is moistening such as pin-wheeling and point-releases below cliffs.
  • Avoid terrain traps such as gullies and cliffs where small avalanches can have high consequence.

Avalanche Summary

Over the past three days, several wet loose avalanches were observed at tree line and below, primarily on sunny aspects. Some of these stepped down to basal facets in northern parts of the region.

On Friday, a remote-triggered size 2 persistent slab was reported near Stewart, running on an east facing rib feature near 1600m. The slab (30-120cm thick) failed on the mid January layer, with surface hoar 4-8mm reported.

Snowpack Summary

Recent warming has melted and refrozen the snow surface at higher elevations. Expect the snow surface to be wet or a melt-freeze crust on all aspects except for possibly high elevation north facing. Strong easterly to southerly winds have redistributed any available soft snow and produced variable surfaces at high elevations, including wind slabs in lee and cross-loaded features. This overlies a sun crust on solar aspects and 5 to 20 mm surface hoar on sheltered, shady aspects at all elevation bands.

Beneath this, layers of crusts, facets, and isolated surface hoar buried 50 to 100 cm exist below the surface from mid- and late-February. A surface hoar and 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

Not much change in the weather pattern: A mix of sun and increasing cloud and little if any precipitation until Tuesday.

SUNDAY: Partly cloudy / Light northerly winds / Alpine temperature +1 C / Freezing level 1400 m.

MONDAY: Cloudy with isolated flurries / Light to moderate north westerly winds / Alpine temperature near 0 degrees C / Freezing level 1200 m.

TUESDAY: Scattered flurries (5-10 cm possible) / Moderate westerly winds / Alpine temperature near 0 degrees C / Freezing level 700 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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