Avalanche Forecast

Issued: Mar 20th, 2019 4:23PM

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

Avalanche Canada cgarritty, Avalanche Canada

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Slight cooling and increasing cloud may take the edge off loose wet avalanche problems on Thursday, but greenhouse effect may destabilize north aspects. It's still a tricky time to be in avalanche terrain. Get an early start if you're heading out.

Summary

Confidence

Moderate -

Weather Forecast

Wednesday night: Clear. Light south winds. Freezing levels remaining near 2900 metres.Thursday: Mainly sunny with cloud increasing in the evening. Light to moderate south winds increasing over the day. Alpine temperatures dropping from about +5 to +1 as freezing levels descend from 2700 to 2300 metres.Friday: Cloudy with sunny periods and scattered rain showers or wet alpine flurries beginning in the evening. Light to moderate east winds. Alpine high temperatures around +5 with freezing levels to 2400 metres, dropping in the evening to 1500 metres by mid-morning Saturday.Saturday: Cloudy with wet flurries bringing up to 8 cm of new snow to higher elevations by end of day, easing overnight. Rain below about 1100 metres. Light southwest winds. Alpine high temperatures around -1 with freezing levels around 1500 metres.

Avalanche Summary

Observations in the Skeena corridor and Shames area on Sunday through Tuesday 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

Between 50 and 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 on shaded aspects at higher elevations, and surface hoar in shaded and sheltered locations. This variable layer has been the primary failure plane in recent slab avalanche observations.Not much further below this storm snow interface is a second weak layer buried on February 19, primarily made up of weak facets and surface hoar crystals. Recent loose wet and slab avalanches have been observed gouging into the faceted snow in this layer, thereby entraining additional mass.The lower snowpack is generally strong.

Problems

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 sustained warming causing loose wet avalanche problems to include shaded aspects.Avoid exposure to steep, sun exposed slopes while solar radiation is strong.Be aware of overhead hazards and avoid lingering in runout zones.

Aspects: North East, East, South East, South, South West, West, North West.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

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.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1.5 - 3

Valid until: Mar 21st, 2019 2:00PM

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