Avalanche Forecast

Issued: Mar 21st, 2019 4:44PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Persistent Slabs and Loose Wet.

Avalanche Canada jsmith, Avalanche Canada

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Avoid steep, rocky terrain in the alpine where there is a shallow or highly variable snowpack depth. This will reduce the likelihood of triggering large persistent slab avalanches.

Summary

Confidence

High -

Weather Forecast

THURSDAY NIGHT: Partly cloudy / Moderate, southeasterly winds / Alpine low 5 C / Freezing level 2200 m.FRIDAY: Mostly cloudy with sunny periods / Moderate, southeasterly winds / Alpine high 5 C / Freezing level 2200 m.SATURDAY: Snow/rain; 5-10 mm precipitation / Strong, southerly winds / Alpine high -1 C / Freezing level 1300 m.SUNDAY: Mix of sun and cloud / Light, southeasterly winds / Alpine high 0 C / Freezing level 1500 m.

Avalanche Summary

Observations in the Skeena corridor and Shames area on Sunday through Wednesday have been showing evidence of the ongoing natural avalanche cycle affecting all aspects and elevations. Numerous natural loose wet avalanches continue to be observed, with some reaching size 3 (very large). Explosives control yielded slabs that initiated at the March 10 interface but gouged deeply into isothermal (slushy) and faceted (sugary) snow. Observations show the largest loose wet avalanches reaching the full extent of their respective avalanche paths.Initial reports of the avalanche cycle came from the Shames area on Sunday, with several very large (size 3) slab avalanches observed running full path with more numerous audible large avalanches. This initial activity was focused on steep, sun-exposed aspects. The March 10 interface has been the primary failure plane in slab releases.Avalanche activity has been similar if not more pronounced in the Bear Pass area and further north.Expect the heightened avalanche activity described above to continue while temperatures remain elevated and overnight cooling weak.

Snowpack Summary

50-100 cm of settled snow forms the upper snowpack at higher elevations, the product of storms since the drought ended on March 10. At lower elevations this precipitation came as rain. With the help of warm temperatures, this recent snow has either settled into a slab on shaded aspects or become increasingly isothermal (slushy) on sun-exposed aspects. Where it exists as a slab, it covers a variety of old snow surfaces left in the wake of the drought. These include crusts on solar aspects, facets (sugary snow) on shaded aspects at higher elevations, and surface hoar (weak, feathery crystals) in shaded/sheltered locations. This variable layer has been the primary failure plane in recent slab avalanches.Not much further below this storm snow interface is a second weak layer buried on February 19, primarily made up of weak facets or surface hoar. Recent loose wet and slab avalanches have been observed gouging into this faceted snow and entraining additional mass.The lower snowpack is generally considered to be strong in most areas, except for rocky areas in the alpine with a shallow or highly variable snowpack depth.

Problems

Persistent Slabs

An icon showing Persistent Slabs
Previous weaknesses in the upper snowpack remain active. A weak layer buried around 60 cm below the surface is still sensitive to triggering. Heightened avalanche activity in the upper snowpack is expected to continue as warm temperatures persist.
Loose wet avalanches may initiate slab releases that result in even larger avalanches.Avoid steep, rocky terrain in the alpine where there is a shallow or highly variable snowpack depth.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1.5 - 3

Loose Wet

An icon showing Loose Wet
Sunshine and warming will destabilize surface snow - especially on steep, sunny slopes. This problem may to expand to include shaded aspects under sustained warming. Large loose wet avalanches have been entraining mass and impacting lower elevations.
Be aware of overhead hazards and avoid lingering in runout zones.Avoid exposure to steep, sun exposed slopes while solar radiation is strong.Be aware of sustained warming causing loose wet avalanche problems to include shaded aspects.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Valid until: Mar 22nd, 2019 2:00PM