Avalanche Forecast

South Rockies

Date issued

Mar 1, 2018 - 4:45 PM

Valid until

Mar 2, 2018 - 2:00 PM

Prepared by

jmcbride

A strong southeast flow is expected to bring more snow Thursday night into Friday. Amounts are uncertain but expect to find new storm slabs building especially at upper elevations.

Regular season
Thursday - March 1, 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.

Friday - March 2, 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.

Saturday - March 3, 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?

New snow and wind may form touch storm slabs particularly on lee and cross-loaded slopes at and above treeline.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • If triggered, the wind slabs may step down to deeper layers, resulting in large avalanches
  • Watch for signs of instability such as whumpfing, or cracking.

Avalanche Problem 2: Deep Persistent Slabs

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

Deeply buried weak layers are most likely to be triggered from thin or variable snowpack areas; or with a large load, like a cornice fall.

Travel and Terrain Advice
  • Avoid steep convexities or areas with a thin or variable snowpack.
  • Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.

Avalanche Summary

Over the past week there have been reports of both natural and skier triggered loose dry avalanches in steep terrain, as well as skier and explosive triggered storm slab avalanches up to size 1 that were reported on Monday.

Last weekend there were two reports of snowmobilers triggering a size 1.5 and size 2 wind slab releases on northeast to east aspects between 2000-2100 m in the Window mountain area.

Snowpack Summary

About 15-30 cm of new snow now covers previously wind-scoured, westerly slopes and old hard and soft wind slabs on leeward, easterly alpine and treeline slopes. Beneath these old wind slabs lies a well-settled mid-pack.

The lower snowpack is weak with two primary concerns that are generally widespread:

1) A widespread weak layer from mid-December composed of facets, crusts, and surface hoar that is 100-150 cm deep.

2) A rain crust with sugary facets buried in late November near the bottom of the snowpack.

Weather Forecast

TONIGHT: Snow. Accumulation 5-15. Ridge wind moderate, east. Temperature near -8. Freezing level lowering to valley bottom.

FRIDAY: Cloudy, snow. Accumulation 5-15 cm. Ridge wind light, northeast. Temperature near -4. Freezing level 600 m.

SATURDAY: Mainly cloudy, light flurries. Accumulation 2-5 cm. Ridge wind light, northeast. Temperature near -6. Freezing level 600 m.

SUNDAY: Mix of sun and cloud. Ridge wind light, west. Temperature near -6. Freezing level 500 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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