Purcells

Be prepare to dial back your terrain choices if signs of instability are present as new snow sits on a slippery buried surface hoar layer. Hazard will deteriorate throughout the day - especially where new snow exceeds 15 cm and/or wind starts transporting snow into wind slabs.  

An offshore low will push bands of warm and moist air in upcoming days which make it challenging to forecast the precise timing, temperatures and total snowfall amounts. Where they "stall", higher snow fall amounts will accumulate.

Saturday night: Mainly cloudy with clear periods and isolated flurries, trace to 2 cm new snow, moderate southwest ridge wind gusting strong and alpine low temperature around -8C.

Sunday: Cloudy with snow, 5-10 cm of new snow, light south ridge wind gusting strong, alpine high temperatures around -5C and freezing levels 800 m to 1000 m.

Monday: Snow, heavy at times, 10-20 cm of new snow, light south ridge wind gusting strong, alpine high temperatures around -3C and freezing levels 700 m to 1600 m.

Tuesday: Cloudy with snow, 10 cm of new snow, light south ridge wind gusting strong, alpine high temperatures around -4C and freezing levels 700 m to 1500 m.

A few small slab avalanches (size 1-1.5) were reported on Friday or Saturday. On the 29th a MIN from the back-country near Kicking Horse reported 15 cm recent storm and that they could skier trigger small slab avalanches on the Jan 27 surface hoar. The AvCan field team reported a small wind slab under a cornice in the Hellroaring creek. A MIN from near Kicking Horse on the 28th reported that wind slabs were developing in lee deposition zones at treeline on northeast aspects as evidenced by a skier triggered small avalanche (size 1.5) that was 30cm deep and ran for 300 m. These isolated reports offers clues as to what will happen once a larger load of snow adds wieght to this surface hoar layer in upcoming days. On Thursday in the Golden area,small but reactive new wind slabs and cornice growth was reported. Farther south from the mountains east of Kimberlyl this MIN from the 28th reports 20-30 cm of recent snow that rested on a firm wind/sun crust.  

We're continuing to track a layer of surface hoar from early January. Two MIN reports (MIN report 1; MIN report 2) from north of the region in Hope Creek report human-triggered slab activity from January 20. This MIN report from the Quartz zone (from Jan 14) shows a reactive layer of Jan 11th surface hoar on north-facing slopes near treeline. Concern for this layer is increasing in line with loading from new snow and increased avalanche activity in shallower snowpack layers.

Light snow is forecast overnight Saturday, with another 5-10 cm forecast Sunday by 4pm. This adds to the 10 to 30 cm of low density snow that accumulated in the region by Friday. This 15-40 cm of new snow will buried a variety of surfaces including a surface hoar layer, a thin sun crust on steep solar, scoured and pressed surfaces in exposed terrain as well as more variable wind affected and faceted snow in sheltered terrain. The buried a layer surface hoar was reported as widespread in sheltered areas in the alpine and treeline and widespread below treeline. 

A second weak of layer of surface hoar and / or a thin melt crust from Jan 11th is down 30-70cm. In recent snowpack tests at treeline elevations near Golden this layer produced sudden results. This persistent weak layer is most suspect in sheltered, open slopes at treeline and warrants slope-specific investigation if you're travelling in the north of the region. Concern for this problem increases with additional snow and warm temps, particularly since a smaller avalanche may step down to this layer, especially in shallower snowpack layers.

Two deeper layers remain on our radar, though they have been recently unreactive. Down 100-150 cm lies the December weak layers, which is consists of a combination of 2 different decomposing surface hoar layers, a crust and faceted snow. Near the grounds a notable rain crust from early November that is surrounded by a weak layer of sugary facets. Though unlikely to trigger, caution for these layers remains with large loads in steep, shallow, rocky areas with a thin to thick snowpack. There is also concern for these layers in isolated below treeline locations.

• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
• Make observations and assess conditions continually as you travel.
• Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
• Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.