Purcells

Recent snow with wind is likely to form reactive slabs. Avoid drifted areas and assess open slopes and rollovers where a weak layer may be preserved. 

Sunday night: Mostly cloudy, moderate northwest winds, freezing level dropping to valley bottom.

Monday: A mix of sun and cloud, light northwest winds, alpine high temperatures near -10 C.

Tuesday: Increasing cloud, winds shifting to the southwest and increasing to moderate, alpine high temperatures near -9 C.

Wednesday: Mostly sunny, light northwest winds, alpine high temperatures near -14 C. 

No new avalanches were reported over the weekend. Recent snow and wind will likely form fresh slabs that may be sensitive to human triggering on Monday. Cornices may be reaching their breaking point and can act as triggers on slopes below. 

Avalanches breaking in the recent snow have the potential to step down to deeper layers, creating larger and more destructive avalanches. There is uncertainty as to how a weak layer of surface hoar buried Jan 11th will react to the recent new snow and wind. This MIN report from the Quartz zone on Thursday shows the reactive layer of surface hoar on north-facing slopes near treeline. 

In the aftermath of the storm last Tuesday, we received reports of avalanches reaching size 3 in the central part of the region, lending support to the idea that some larger releases may have involved persistent weak layers. Although avalanche activity on more deeply buried weak layers from early December and November has been isolated, the possibility exists for the load from new snow and wind to reactivate these deeper instabilities. 

Incremental accumulations over the weekend varied across the region, with 10 cm falling in the north near Quartz and Toby Creeks and with up to 5 cm in the south near Kimberley. Winds have switched direction from the south to the northwest, creating a tricky reverse-loading pattern at upper elevations. Observers report extensive wind-affect at treeline and alpine elevations (check out these MINs from Hiroshima trees, Jumbo, and Mt Gill). Ongoing snow and wind have contributed to notable cornice growth. 

30-60 cm of snow from the past week has buried a weak of layer of surface hoar. On solar aspects, this layer may be found near a thin crust. This persistent weak layer is more likely to be preserved at elevations above where a thick crust exists and below more wind-affected terrain. It is most suspect in sheltered, open slopes at treeline.

A deeper layer (from early December) may be found 90-140 cm down. It consists of a combination of decomposing surface hoar with a crust and faceted snow.

Avalanche activity on this layer has dwindled since last week, with snowpack tests results showing some variability between sudden and more resistant propagation.

The lower snowpack is characterized by a notable rain crust from early November that is surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers in steep, shallow, rocky areas with a thin to thick snowpack.

• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.