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Avalanche Forecast

Archived

Apr 23rd, 2021–Apr 26th, 2021

Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

North Columbia.

Generally safe avalanche conditions this weekend may deteriorate into next week. Re-evaluate avalanche danger and ease into terrain cautiously after any big changes in the weather. This is the last forecast for the season. Thanks for the great winter and play safe!

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Friday night: Clear, light wind, alpine temperature near -5, freezing level valley bottom.

Saturday: Mostly cloudy with isolated flurries up to 5 cm, light wind, alpine high near -5, freezing level 1600 m.

Sunday: Mostly cloudy with isolated flurries, light wind, alpine high near -5, freezing level 1600 m.

Monday: Mix of sun and cloud, moderate southwest wind, alpine high near -2, freezing level 2100 m.

Avalanche Summary

Warm temperatures last week resulted in widespread wet avalanche activity. The most notable activity was on Saturday where there was both widespread size 1-2 wet loose avalanches and a few larger and destructive (size 2.5-3.5) wet slab avalanches. The large wet slabs were mostly on south and west facing slopes. Avalanche activity has been on the decline since then with relatively cooler temperatures. A cornice fall triggered a large (size 3) slab avalanche on a north-facing alpine ridge in Glacier National Park on Tuesday.

The cooling trend will make wet avalanches problems unlikely in the coming days, making cornices the primary concern. 

Snowpack Summary

The upper snowpack has undergone multiple melt-freeze cycles and is now crusty and refrozen in the cooler temperatures. Dry snow may still be found on northerly aspects above roughly 2300 m. There are no layers of concern in the snowpack, which has been melting and settling over the past week. Large cornices loom along many ridgelines.

Terrain and Travel

  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Carefully evaluate steep lines for wind slabs.

Problems

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.