Avalanche Forecast

South Rockies

Date issued

Mar 20, 2018 - 5:25 PM

Valid until

Mar 21, 2018 - 2:00 PM

Prepared by

swerner

Pay close attention to how the new snow is bonding to the old snow surfaces, especially where it sits on surface hoar and buried crusts.

Regular season
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

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.

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

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.

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.

Avalanche Problem 1: Storm Slabs

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

Watch for signs of poor bonding of the new snow with underlying surfaces, especially the March 18th crust, which can be found almost everywhere except high north facing aspects. Dry loose sluffs may run fast and far on slippery crusts.

Travel and Terrain Advice
  • Use caution in lee areas in the alpine and tree line, especially south / west facing slopes.
  • Observe for signs of instability, such as cracking, whumpfing, and avalanche activity.

Avalanche Problem 2: Loose Wet

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

If the sun comes out on Wednesday, expect the new snow to become reactive and/or slide naturally, especially from steep solar aspects.

Travel and Terrain Advice
  • Watch for signs that the snow is moistening such as pin-wheeling and point-releases below cliffs.
  • Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
  • Avoid exposure to sunny slopes

Avalanche Summary

On Tuesday, one size 1 wind slab was reported, entraining moist snow during warming. A few natural loose dry avalanches up to size 1.5 occurred on Monday.

Snowpack Summary

Up to 25 cm of low density snow fell Sunday overnight into Monday, combined with last weeks snow, this brings the total amount 30-40 cm. This new snow sits on a wide variety of old surfaces: a melt-freeze crust on sunny aspects, isolated old wind slab in the alpine near ridge crests and predominantly dry snow or surface hoar (up to 20mm in size) on north aspects above 1500-1800m.

A weak layer of surface hoar buried mid-February exists in parts of the region around 50 to 80 cm deep. The lower snowpack is weak with a combination of crusts and facets near the bottom of the snowpack that are widespread.

Weather Forecast

Wednesday: Mix of sun and cloud. Alpine temperatures near -2 and freezing levels near 1900m. Ridgetop winds light from the South.

Thursday: Snow amounts 5-10 cm, accompanied by strong ridgetop winds from the southeast. Freezing levels near 1700 m.

Friday: Cloudy with isolated flurries. Alpine high of -11 and freezing levels near 1500 m. Light to strong gusty southwest winds.

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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