Avalanche Forecast

Issued: Mar 13th, 2017 4:46PM

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

mgrist, Avalanche Canada

North Columbia.

Snow, strong wind and warming are a recipe for HIGH danger. Conservative terrain use at all elevations is essential this week. Avoid overhead hazard and choose simple terrain!

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

We'll see warmer temperatures with strong winds and significant precipitation through the forecast period. TUESDAY: Snow (10-20cm) with STRONG southwest winds. Freezing levels near 1800m.WEDNESDAY: Another 15-25cm of fresh snow throughout the day accompanied by moderate south winds. Freezing levels remain at 1800m.THURSDAY: Flurries with another 5cm accompanied by moderate southwest winds. Freezing levels dropping to 1200m.

Avalanche Summary

On Monday a widespread natural avalanche cycle to Size 2.5 was reported on a range of elevations and aspects. On Sunday, several large avalanches (up to Size 4) were reported with artillery control in Glacier National Park, some running full path to valley floor.On Sunday several small natural storm slab avalanches were reported near Revelstoke below treeline. Use extra caution for the time being in what is normally a 'safer' elevation band. See here for the excellent and informative MIN post.

Snowpack Summary

Around 40-60cm of fresh snow has fallen over the past four days (with light to moderate southerly winds). Touchy storm slabs can be found at all elevations with weaknesses within and under this recent snow. Warming temperatures on Sunday into Monday has resulted in moist (read: heavy) surface snow up to 1800m in most areas, and unstable snow below treeline. All this new snow is bonding slowly to faceted snow as well as isolated small surface hoar in sheltered areas and a thin sun crust on steep southerly aspects.The persistent weakness buried mid-February is now down 80-140 cm, and is composed of a thick rain crust as high as about 1800 m, sun crusts on steep southerly aspects, and spotty surface hoar on shaded aspects. Recent reports show the bond to this interface becoming more variable.The mid and lower snowpack are well settled and stable in deeper snowpack areas, but may be weak and faceted in shallow areas. The deep mid-December facet layer still lingers in the northern part of the region near Valemount.

Problems

Storm Slabs

Weaknesses within the recent storm snow are susceptible to human triggering. These storm slabs are particularly deep and touchy on slopes loaded by southerly winds and have the potential to step down to deeper persistent weaknesses.

Be alert to conditions that change with elevation.Avoid convexities or areas with a thin or variable snowpack.The new snow will require several days to settle and stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

2 - 4

Persistent Slabs

Several persistent weaknesses in the upper snowpack remain a concern, and there is step-down potential for slab fractures propagating and resulting in large and dangerous avalanches.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be aware of the potential for wide propagations.Watch for whumpfing, hollow sounds, and shooting cracks.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 4

Valid until: Mar 14th, 2017 2:00PM