Date issued

Apr 28, 2018 - 4:00 PM

Valid until

Apr 29, 2018 - 4:00 PM

Prepared by

snow safety

Overnight rain will cause natural avalanches. While refreeze is expected up high by noon, The snowpack is unlikely to recover before Monday. A good day to avoid travel in the mountains.

Spring Season Conditions

Avalanche Problem 1: Loose Wet

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

Rain on a relatively warm snowpack will certainly cause avalanches overnight Saturday

Avalanche Problem 2: Persistent Slabs

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

A few deeper avalanches have occurred in the last few days. Some stepped down to the March 15 crust. On shaded aspects these were likely sliding on facets formed at the same interface. This will wake up again with intense heating or large triggers.

Travel and Terrain Advice
  • Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.
  • Avoid shallow snowpack areas where triggering is more likely.

Avalanche Problem 3: Cornices

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

Cornice failures are occurring on a regular basis now with warm temperatures and intense solar inputs. These large triggers have caused failures on the persistent weak layers deeper in the snow pack in a few places in the last couple days.

Travel and Terrain Advice
  • Minimize exposure to overhead hazard from cornices.

Avalanche Summary

The last few days have seen many wet avalanches up to size 3 running on all aspects in the afternoon and early evening.

Snowpack Summary

Isolated wind slabs are present in the alpine. Crust or moist snow on all solar aspects depending on temperatures. Buried temperature crusts to 2000m on all aspects and to ridge top on solar slopes, including the Mar 15 crust down 40-70 cm in the alpine. Moist snow at lower elevations, with the entire snowpack becoming moist near valley bottom.

Weather Forecast

Rain is forecast overnight Saturday and into Sunday. This, combined with the warm temperatures from last week will almost certainly preclude recovery and lead to high hazard in the morning. Temperatures will cool Sunday and will likely refreeze the snow at Treeline and in the Alpine. Isothermal snow can be expected below treeline throughout the day

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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