Avalanche Forecast

Archived

Apr 23rd, 2021–Apr 26th, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

South Columbia.

Heightened danger ratings reflect up to 30 cm of new snow forecast at upper elevations in the south of the region by Sunday. Fresh snow will be sensitive to the sun on Monday. This is the last forecast of the season. Thanks for the great winter and play safe!

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

Friday night: Partly cloudy, light wind, alpine high near -3, freezing level 2000 m.

Saturday: Flurries bringing up to 5 cm, light wind, alpine high near -4, freezing level 1700 m.

Sunday: 15-30 cm new snow in the south of the region, trace in the north, light southwest wind, alpine high near -4, freezing level 1700 m.

Monday: Flurries bringing up to 5 cm, moderate westerly wind, alpine high near -4, freezing level 1700 m.

Avalanche Summary

Warm temperatures last week resulted in widespread wet avalanche activity. The most notable activity was last 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.

Looking forward, we may see some storm slab activity in the new snow on Sunday and solar triggered loose snow avalanches will be likely on Monday.

Snowpack Summary

In the south of the region, up to 15-20 cm of new snow is forecast to fall by Sunday, while the north may see a light dusting. The new snow falls over a thick surface crust. 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 2400 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.
Make observations and assess conditions continually as you travel.
Closely monitor how the new snow is bonding to the crust.
Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

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.