Avalanche Forecast

Issued: Jan 17th, 2015 7:46AM

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

jlammers, Avalanche Canada

South Columbia.

A storm on Sunday will increase the Avalanche Danger. Conservative terrain selection will become increasingly important.

Summary

Confidence

Fair - Intensity of incoming weather systems is uncertain on Sunday

Weather Forecast

A moist pacific frontal system will cross the region on Sunday bringing moderate to locally heavy amounts of snow. Weather models are in high disagreement with forecast snowfall amounts ranging from 15cm to 30cm falling between Sunday morning and Sunday night. Unsettled conditions with light flurries are expected on Monday before a dry ridge of high pressure builds on Tuesday. Winds are expected to be strong from the southwest on Sunday, dropping to light and westerly on Monday and Tuesday. Freezing levels will peak at about 1400m on Sunday and Monday, and then drop to valley bottom on Tuesday.

Avalanche Summary

Natural and human-triggered wind slab activity to size 2 was observed in response to new snow and wind on Friday night. With more snow and wind forecast for Sunday, I would expect the developing storm slab to increase in size and reactivity. An avalanche in motion may also "step down" to a deeper, more destructive weak layer which was buried in mid-December.

Snowpack Summary

Up to 20cm of new snow has buried widespread 10-20mm surface hoar, a sun crust on steep sun exposed slopes, and/or wind affected surfaces in the alpine. More snow and wind forecast for Sunday will increase the size and reactivity of the developing storm slab. The problematic mid-December surface hoar/crust layer is typically down 80-120cm below the surface, and may still be sensitive to human triggering. The reactivity of this persistent weak layer appears to be quite variable but still has the potential for large, destructive avalanches in some areas. The layer appears to be the most reactive in the south of the region at and below treeline.

Problems

Storm Slabs

New snow and wind on Sunday will add size and reactivity to a developing storm slab. The new snow is expected to be especially reactive due to underlying weak crystals.

Be cautious as you transition into wind affected terrain.>Stay off recent wind loaded areas until the slope has had a chance to stabilize.>The new snow will require several days to settle and stabilize.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

The mid-December weak layer remains problematic at and just below treeline where the snowpack structure may still be primed for human triggering in some areas. The weight of the new snow may increase the reactivity of this layer.

Use conservative route selection, stick to moderate angled terrain with low consequence.>Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Valid until: Jan 18th, 2015 2:00PM