Avalanche Forecast

Archived

May 7th, 2017–May 8th, 2017

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Regions

Little Yoho.

Some good spring travel conditions exist at high elevations. Watch for clear cool nights in the forecast, then start early to complete your objective before daytime warming causes the snowpack to become weak.

Weather Forecast

The week of May 8-14 looks like a clearing and gradually warming trend. The first part of the week looks like the best time to get out and enjoy a good overnight freeze while the later part of the week may not have much of an overnight crust recovery. No significant precipitation is expected until late in the week.

Snowpack Summary

Isothermal snow exists at lower elevations. Crusts formed during clear cool nights will break down quickly with solar inputs. Expect moist surface snow to mountain top in the afternoon with the exception of high elevation North slopes. The basal facet weakness persists at treeline and above and is reactive to large triggers or warm temperatures.

Avalanche Summary

Large wet slab avalanches failing on the basal facets have been observed during recent periods of rapid heating or with large triggers such as cornices at treeline and above. These are running far with lots of destructive potential. Loose wet avalanches are being reported whenever the surface snow becomes wet with daytime heating.

Confidence

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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.