Avalanche Forecast

Issued: Jan 28th, 2013 8:39AM

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

jfloyer, Avalanche Canada

Cariboos.

Ratings are based on the region staying mostly dry on Tuesday morning. If you do see significant snowfall (20+ cm) by noon on Tuesday, consider ratings to be High / Considerable / Considerable.

Summary

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

Synopsis: Northwesterly flow will bring a series of moderate or locally heavy pulses of precipitation to the region through the forecast period.Tuesday: Should stay cold (-12C) and dry for the first half of the day. Moderate or locally heavy precipitation beginning in the afternoon, with 10-20 cm expected by Wednesday morning. The heaviest snowfall is likely to be found to the north and east of the region. Treeline temperatures rising to around -8C. Northwesterly winds, gusting to 60km/h at ridgetop during the afternoon.Wednesday: Further light snowfall, around 5 cm. Treeline temperatures peaking around -2C. Strong northwesterly winds gusting to 50km/h at ridgetop.Thursday: Dry, cold (-12C) with generally light northwesterly winds.

Avalanche Summary

No new avalanches were reported through the weekend. On Friday, a couple of small (size 1) avalanches were triggered on convex rolls by ski cutting on south aspect slopes.

Snowpack Summary

Around 40-50 cm recent new snow has settled into a 20-30 cm soft slab overlying a weak layer comprising of facets at higher elevations, surface hoar on shady slopes, and a sun crust on solar aspects. The recent new snow sitting above this interface has been slowly consolidating from fresh powder into a more cohesive slab. As this process continues, the avalanche character will change from relatively harmless loose sluffs to more dangerous slab avalanches. However, note this upper weak layer has been reported to be patchy and variable in distribution. A mid-pack layer buried in early January surface hoar layer is down 70-90 cm. While this layer is still on the radar of professional observers, with most likely trigger points being on steep rolls below 1600 m, there has only been one small avalanche (size 1 at 1200 m on a north aspect) reported on this layer from the region for approximately 10 days.

Problems

Storm Slabs

Recent storm snow is settling into a soft slab in many areas. Where this overlies surface hoar or a crust it will become increasingly touchy. Pockets of wind slab exist behind ridges where the snow is protected from a S or W wind. Watch fat pillows.

Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>Avoid freshly wind loaded features.>Highmark or enter your line well below ridge crests to avoid wind loaded pillows.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 4

Persistent Slabs

Two surface hoar layers lie buried under the surface, one approximately 40cm down and the other approximately 80cm down. Both are reported to be patchy and variable in distribution. Most likely triggered on steep convex rolls at treeline or below.

Whumpfing is direct evidence of a buried instability.>Avoid steep convex rolls at and below treeline where buried surface hoar may be preserved.>Dig down to find and test weak layers before committing to a line on steep slopes in open glades.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Jan 29th, 2013 2:00PM