Avalanche Forecast

Issued: Jan 18th, 2015 8:21AM

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

Purcells.

Check out the most recent Forecaster Blog for more details on the current conditions. http://www.avalanche.ca/blogs/VLsBsCgAACYAJdfM/mid-jan-sh

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

Unsettled conditions and light flurries are expected on Monday as a pacific frontal system exits the region to the southeast. By Tuesday a weak dry ridge of high pressure will rebuild. Confidence in the forecast for Wednesday gets shaky on Wednesday as weather models disagree on the ridge's ability to deflect a system creeping in from the northwest. Stay tuned! On Monday, ridgetop winds are expected to be moderate from the west, dropping to light from the northwest on Tuesday and Wednesday. Freezing levels should hover around 1400m on Monday, and then drop to near valley bottom for Tuesday and Wednesday.

Avalanche Summary

Natural and human-triggered wind slab activity to size 1.5 was observed in response to new snow and wind on Friday night. With more snow and wind on Sunday, I expect there was more potent storm slab activity at higher elevations with loose dry avalanches running in sheltered terrain. An avalanche in motion may also "step down" to a deeper, more destructive weak layer which was buried in mid-December.

Snowpack Summary

Between 15cm and 40cm of new snow has buried widespread 10-20mm surface hoar and a sun crust on steep sun exposed slopes. Strong winds have blown these accumulations into deeper deposits in higher elevation terrain. The problematic mid-December surface hoar/crust layer is typically down 40-80cm below the new snow and remains sensitive to human triggering is some areas. 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 at and below treeline. The mid-Nov weak layer is near the bottom of the snowpack but has generally become inactive.

Problems

Storm Slabs

New snow and wind from Sunday has added size and reactivity to a developing storm slab. The new snow is expected to be especially reactive due to underlying weak crystals. In sheltered terrain, expect loose dry avalanche activity.

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.>Be cautious as you transition into wind affected terrain.>Be cautious of sluffing in steep terrain.>

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.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Jan 19th, 2015 2:00PM