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 unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Purcells.

Heightened danger ratings reflect ~20 cm of new snow forecast to fall at upper elevations in the south of the region by Sunday. Fresh snow will be sensitive to solar triggering 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

Local precipitation enhancements in the south of the region may accumulate up to 30 cm by Sunday.

Friday night: Mostly cloudy, light to moderate northwest wind, alpine high near -5, freezing level 1000 m.

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

Sunday: 5-15 cm new snow, moderate southwest wind, alpine high near -4, freezing level 1700 m.

Monday: Overnight flurries bringing up to 5 cm, then a mix of sun and cloud. Moderate to strong westerly wind, alpine high near -4, freezing level 2000 m.

Avalanche Summary

Warm temperatures last week resulted in widespread wet avalanche activity, primarily on sun-exposed slopes. Most of the activity was size 1-2 wet loose avalanches, but a few larger and destructive wet slab avalanches were reported near the Bugaboos on Saturday and near Golden on Monday. Some large cornice falls were also observed.

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 30 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. We suspect older weak layers have gone inactive as the weather patterns over the past month have been favorable for strengthening the snowpack.

Terrain and Travel

Make observations and assess conditions continually as you travel.
Dial back your terrain choices if you are seeing more than 20 cm of new snow.
Wind slabs may be poorly bonded to the underlying crust.
Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Minimize exposure to sun-exposed slopes when the solar radiation is strong.

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.