Avalanche Forecast

Issued: Jan 5th, 2017 4:59PM

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

mgrist, Avalanche Canada

Purcells.

Persistent weaknesses deeper in snowpack still can't be totally trusted. Approach big open slopes with caution, especially in shallow snowpack areas.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

We're beginning to see a shift from the very cold conditions of late with daytime temperatures warming up by 5-10 degrees Celcius. Only some isolated flurries possible until late Sunday when a small amount of light dry snow may fall (5-15 cms).FRIDAY: Up to 5cms light dry snow possible Thursday overnight into Friday. Mainly cloudy Friday with winds becoming southwesterly 15-25 Km/h. Alpine high temperatures near -14 and lows to -24 Celcius overnight. SATURDAY: Sunny breaks with increasing clouds in the evening. Slight chance of flurries. Winds light southerly. Alpine high temperatures near -12 and lows to -22 Celcius.SUNDAY: Increasing clouds. Wind light and variable. Alpine high temperatures near -12 Celcius; 5-15 cms light dry snow possible overnight.

Avalanche Summary

Small, predictable skier-triggered avalanches (thin windslabs) were reported yesterday. Reports from earlier in the week were limited to a few Size 1-2 wind slab avalanches triggered naturally and by explosives. Wind slabs may remain reactive to human triggers in specific areas, such as the immediately lee of ridges and sun-exposed slopes.

Snowpack Summary

Surface hoar is growing and the upper snowpack is faceting. In exposed areas at all elevations, recent winds have resulted in scouring, hard wind slabs, and thicker reactive wind slabs in unusual places as the winds shifted from west to northeast. Continued moderate variable winds have been keeping wind-slabs fresh and touchy in some areas and sun-exposure is likely making the wind slabs extra touchy on south-facing slopes. Facets and/or surface hoar buried mid-December has been giving hard and broken or no results in snowpack tests where it is down close to a metre. However, recent snowpack tests in a shallower area, gave moderate sudden planar results on this persistent weakness where it was found as surface hoar down 20-30 cm. This suggests that the primary concern for persistent slab avalanches is in shallow snowpack areas; however, the potential for step-down avalanches remains where it is deeper. The lower snowpack is well bonded and features a thick rain crust near the ground.

Problems

Wind Slabs

Weak wind slabs are lurking below ridgecrests and behind terrain breaks in exposed terrain on all aspects.

Avoid travelling in areas that have been reverse loaded by winds.Use ridges or ribs to avoid pockets of wind loaded snow.Be cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

Surface hoar and/or facets buried mid-December remains a concern in shallow snowpack areas.

Avoid convexities or areas with a thin or variable snowpack.Dig down to find and test weak layers before committing to a line.Be aware of the potential for large avalanches due to the presence of buried weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely

Expected Size

1 - 3

Valid until: Jan 6th, 2017 2:00PM