Avalanche Forecast

Archived

Mar 17th, 2021–Mar 18th, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

South Columbia.

Spring-like diurnal conditions exist and the rating reflects the highest hazard level anticipated during the day with warming. Pay attention to steep south facing slopes as they heat up in the afternoon and destabilize. Give looming cornices a wide berth from above and below.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

A Pacific frontal system approaching the coast on Thursday will start to force some upper-level cloud cover to the Interior Mountain Ranges. Freezing levels will be between 1500-2000 m. By Friday the system will bring unsettled weather with new snow and cloudy skies.

Thursday: Mix of sun and cloud. Alpine temperatures near +1 and freezing levels 2000 m. Ridgetop wind strong from the southwest.

Friday: Mostly cloudy with 5 cm of new snow. Alpine temperatures near -5 and freezing levels 1600 m. Ridgetop wind moderate from the southwest.

Saturday: Cloudy with snow 5-10 cm. Alpine temperatures near -6 and freezing levels 1300 m. Ridgetop wind moderate from the southwest.

Avalanche Summary

On Tuesday, a natural 1.5 loose wet avalanche was reported from steep rocky terrain and small loose-dry sluffs were easily triggered by skier traffic on northerly aspects.

Loose wet avalanches and cornice failures may continue with warming Thursday.

Snowpack Summary

Snow surfaces vary at the moment. Surface hoar up to 10 mm in size exists at treeline and above. Sunny skies and warm temperatures formed sun crusts on solar aspects and at all elevations and up to 2000 m on polar aspects. Dry snow still exists on north aspects at upper elevations. Large cornices loom over alpine ridgetops.

Persistent weak layers of surface hoar, crusts, and/or facets 80-120 cm down have recently been unreactive except for an explosives triggered avalanche in the southeast of the region on Saturday.

Terrain and Travel

Cornices become weak with daytime heating or solar exposure.
Back off slopes as the surface becomes moist or wet with rising temperatures.
Rocks will heat up with daytime warming and may become trigger points for loose wet avalanches
When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.