Avalanche Forecast

Archived

Apr 4th, 2021–Apr 5th, 2021

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.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Natural avalanches unlikely.

Regions

Purcells.

Watch for cornices and wind slabs near ridgetops and be cautious on sun-exposed slopes. Moderate danger reflects conditions near Golden where recent snowfall amounts have been highest. Asses conditions in your riding area as you travel.

Confidence

Moderate - Uncertainty is due to field data and reports showing a wide variation in conditions throughout the region.

Weather Forecast

Sunday night: Partly cloudy with isolated flurries. Light northwest wind. Alpine temperatures around -7. Freezing level 800 m.

Monday: Sunny. Light to moderate northwest wind. Alpine high temperatures around -1. Freezing level 2100 m.

Tuesday: Sunny with increasing cloud in the late afternoon. Light to moderate southwest wind. Alpine high temperatures around -1. Freezing level 2200 m.

Wednesday: 5-10 cm new snow. Strong southwest wind easing to light. Alpine temperature around -5. Freezing level 1800 m.

Avalanche Summary

Cornices have been reactive in the last few days both to explosives and naturally, occasionally triggering wind slabs on slopes below.

A natural size 3 was reported on Thursday in the Dogtooth range. It was on a southeast aspect in the alpine and is suspected to have solar-triggered and run on the crust buried in mid-March.

Reports from Wednesday included small (size 1) wet loose point releases from steep solar aspects and explosive triggered wind slabs on north to east facing ridgetops.

Snowpack Summary

The convective nature of Sunday's storm resulted in greatly variable snowfall amounts through the region, as much as 50 cm around Golden and 5-20 cm elsewhere. The recent snow may have seen some wind effect in immediate less of exposed alpine features. Reports indicate it is bonding well to underlying surfaces which include wind affected snow in the alpine or crust on solar aspects and below 1900 m. Below this elevation and on solar aspects the new snow dusts crusty surfaces down to 1500 m. Below 1500 m, the moist snowpack is quickly diminishing.

A widespread crust layer from the mid-March warm spell can be found 30-60 cm deep, and small surface hoar has been observed at this depth on some isolated north-facing slopes. Reports suggest the snow is generally well bonded to these layers but isolated instances of large solar-triggered slab avalanches running on the crust have been observed. Deeper layers are strong and have been unreactive over the past few weeks.

Terrain and Travel

Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.
Rocks will heat up with daytime warming and may become trigger points for loose wet avalanches
Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.