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Avalanche Forecast

Archived

Apr 20th, 2021–Apr 21st, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

South Columbia.

Start and finish you day early as warm sunny weather could cause large avalanches on sun-exposed slopes.

Confidence

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

Weather Forecast

TUESDAY NIGHT: Clear skies, light northwest wind, freezing level drops to 1500 m with treeline temperatures dropping to -2 C.

WEDNESDAY: Sunny with some clouds in the afternoon, light northwest wind with some moderate gusts in the afternoon, freezing level climbs to 2400 m with treeline temperatures reaching +3 C.

THURSDAY: Scattered flurries bring 5-10 cm of snow above 1800 m and light rain in the valleys, light northwest wind, freezing level around 1800 m with treeline temperatures around -2 C.

FRIDAY: Mix of sun and cloud with some isolated flurries, light wind, freezing level climbs to 2000 m with treeline temperatures reaching -1 C.

Avalanche Summary

Avalanche activity has quieted down since temperatures cooled on Sunday. On Saturday there were widespread wet loose and wet slab avalanches on sun-exposed slopes. The wet loose avalanches were mostly size 1-2, but some of the wet slab avalanches were quite large and destructive (size 2.5-3.5). The large wet slabs were mostly on south and west facing slopes.

On Wednesday there is an increased potential for another cycle of large wet avalanches with temperatures staying mild overnight and then freezing levels spiking to 2400 m in the afternoon.

Snowpack Summary

A surface crust will form overnight and then gradually break down with daytime warming. Dry snow may still be found in high north-facing terrain (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

  • Avalanche hazard is expected to to increase througout the day, think carefully about your egress.
  • Avoid exposure to steep sun exposed slopes.
  • Avoid lingering or regrouping in runout zones.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Problems

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.

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

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.