Avalanche Forecast

Issued: Feb 17th, 2018 4:19PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Storm Slabs.

Avalanche Canada jmcbride, Avalanche Canada

Large cornices and storm slabs have formed following Tuesday's big storm event. Watch for wind loaded areas at treeline and above. With the recent wind direction, these may not follow the usual pattern.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SUNDAY: Sunny. Ridge wind moderate to strong, northeast. Temperature -10. Freezing level valley bottom.MONDAY: Mostly sunny. Ridge wind light to moderate, northwest. Temperature -9. Freezing level valley bottom.TUESDAY: Mostly sunny. Ridge wind light, north. Temperature -6. Freezing level valley bottom.

Avalanche Summary

There have been no new reports of avalanches since Wednesday when a widespread natural avalanche cycle up to size 3.5 was reported following the intense loading of Tuesday's storm, with at least one avalanche running beyond it's historical runout distance. Explosive control work on Wednesday produced numerous storm slab releases up to size 2.5, at all elevations. At lower elevations, treeline and below, these slabs were failing on a layer of surface hoar buried by the storm snow on Tuesday.Large cornices have formed as a result of continued winds since Tuesday's storm event. These may weaken with the sun's influence during sunny, clear periods throughout the day.

Snowpack Summary

Approximately 40-60 cm of recent storm snow has fallen across the region since Tuesday with the highest snowfall amounts in the Terrace area.This new snow sits on a wide array of surfaces - including wind scour and old wind slabs at higher elevations on lee (downwind) slopes, as well as sun crusts on steep solar aspects and facets and surface hoar in sheltered locations at treeline and below. Also, a 5-20 cm thick crust/surface hoar layer that was buried early February and can be found 60-110 cm below the surface on all aspects up to 1400 m. In thinner snowpack areas (north and inland), a deeper crust / surface hoar layer that was buried in mid-January in sheltered areas at treeline and below could still be a concern for triggering from shallow spots.

Problems

Storm Slabs

An icon showing Storm Slabs
Storm snow earlier in the week has formed widespread storm slabs. At treeline and below these slabs overlie recently buried surface hoar and have been reactive to light triggers. Recent northerly winds are forming wind slabs in alpine, leeward areas.
Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.Give cornices a wide berth when travelling on or below ridges.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Valid until: Feb 18th, 2018 2:00PM

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