Avalanche Forecast

Northwest Inland

Date issued

Apr 6, 2018 - 3:56 PM

Valid until

Apr 7, 2018 - 2:00 PM

Prepared by

jmcbride

Strong to extreme winds have created wind slabs in leeward areas. Avoid freshly wind-loaded slopes and features, these may be primed for human triggering.

Regular season
Friday - April 6, 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

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.

Saturday - April 7, 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.

Sunday - April 8, 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: Wind Slabs

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

Strong to extreme winds have created touchy wind slabs on leeward and cross-loaded slopes at treeline and above.  While natural activity has likely tapered off, expect these slabs to remain primed for human triggering.

Travel and Terrain Advice
  • Be careful with wind loaded areas, especially near ridge crests and roll-overs.
  • Use caution in lee areas. Recent wind loading has created wind slabs.
  • If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Avalanche Summary

A widespread natural avalanche cycle (up to size 2), triggered by intense wind loading was reported from the northern part of region on Thursday.

A natural, solar triggered size 2 avalanche was reported on Wednesday morning in the Howson range, as well as skier triggered size 1 storm slab releases on a buried sun crust (30 cm deep) on a southeast aspect at 1700 m.

Friday of last week, a natural avalanche cycle up to size 2-3 occurred in response to storm snow loading.

Snowpack Summary

From 20 cm up to 40-50 cm of recent storm snow is being redistributed by strong winds and sits above a variety of crusts on all but high north aspects.

Weak layers buried around March 19th are roughly 40 cm below the surface (up to 100 cm in deeper snowpack areas). These weak layers include surface hoar on shaded aspects at high elevations and hard crust layers on solar aspects and below treeline.

Near the bottom of the snowpack, weak and sugary facets are found in shallow, rocky snowpack areas. Storm slabs have stepped down to these facets and producing very large avalanches in northern parts of the region.

Weather Forecast

TONIGHT: Flurries. Accumulation trace. Ridge wind light to moderate, southeast. Alpine temperature near -10. Freezing level valley bottom.

SATURDAY: Mix of sun and cloud. Ridge wind strong, southeast. Alpine temperature near -3. Freezing level 1200 m.

SUNDAY: Mix of sun and increasing cloud. Ridge wind moderate, southwest. Alpine temperature near -2. Freezing level 1500 m.

MONDAY: Mix of sun and cloud, light flurries. Accumulation trace. Ridge wind moderate to strong, southwest. Alpine temperature near -1. Freezing level 1500 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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