Avalanche Forecast

Northwest Inland

Date issued

Apr 11, 2018 - 4:42 PM

Valid until

Apr 12, 2018 - 2:00 PM

Prepared by

jsmith

Forecast new snow and wind Wednesday night are expected to create fresh wind slabs reactive to human triggers.

Regular season
Thursday - April 12, 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.

Friday - April 13, 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.

Saturday - April 14, 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: Wind Slabs

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

New snow and strong winds will form thin slabs in leeward areas near ridge crests and convex features. These slabs may be touchy were they sit on a recent crust.

Travel and Terrain Advice
  • Use caution when transitioning into wind effected terrain.
  • Avoid areas that look freshly loaded with snow; especially convex features below ridgetops.
  • Avoid shallow, rocky areas where the snowpack transition from thin to thick.

Avalanche Problem 2: Loose Wet

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

Sun and daytime warming are factors to keep in mind. Watch for wet snow on sunny aspects and lower elevation slopes.

Travel and Terrain Advice
  • Watch for signs that the snow is heating up such as pin-wheeling or the surface snow becoming moist.
  • Avoid steep terrain that is in the sunshine.

Avalanche Summary

Numerous natural loose wet avalanches up to size 2 were reported on Tuesday.

Snowpack Summary

Rising freezing levels and daytime warming have created moist or wet snow surfaces on all but alpine, northerly aspects where 20 cm up to 50 cm of recent storm snow has been redistributed by strong winds.

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: 5-10 cm new snow. Light southwesterly ridgetop winds. Freezing level around 500 m.

THURSDAY: Mix of sun and cloud with isolated flurries. Light southwesterly ridgetop winds. Freezing level around 1000 m.

FRIDAY: Mostly cloudy with flurries. Strong southerly ridgetop winds. Freezing level around 1000 m.

SATURDAY: Mostly cloudy with flurries. Moderate southwesterly ridgetop winds. Freezing level around 1200 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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