Purcells

Remain cautious of wind slabs in steep and immediate lee features and be wary of large cornices. Continue to make slope-specific assessments as you step out into steeper and more extreme terrain.

Sunday night: Cloudy / light southwest winds / alpine low temperature -18

Monday: Mostly cloudy, isolated flurries / light south winds / alpine high temperature -10

Tuesday: Cloudy / light southeast winds / alpine high temperature -14

Wednesday: Cloudy with isolated flurries / light variable winds / alpine high temperature -12

Two MIN reports (MIN report 1; MIN report 2) from north of the region in Hope Creek report human-triggered slab activity on Wednesday.

Last Wednesday, operators in neighboring Glacier National Park reported several large (size 2-2.5) wind slabs releasing naturally on a variety of aspects (north, east, and south). Two natural cornice failures were reported in Glacier National Park on Wednesday releasing above north-facing slopes. 

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. Investigate for this layer around sheltered treeline slopes where surface hoar has been preserved. 

Following the mid-January storm, 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 more deeply buried persistent weak layers. Check out this MIN report from Mt McKay. Although avalanche activity on these layers from early December and November has been isolated, the possibility exists for large triggers to reactivate these deeper instabilities. 

Previous winds scoured snow surfaces, loaded cornices, and formed stiff wind slabs in the alpine and around treeline. Cold temperatures are promoting surface faceting. A thin sun crust may be found on steep solar aspects. A widespread layer of surface hoar was reported developing with weekend winds destroying crystals in exposed terrain. Take note of any sheltered areas where surface hoar continues to grow.

30-60 cm of snow buried a weak of layer of surface hoar from Jan 11th. In recent snowpack tests this layer has produced sudden results at treeline elevations in areas near KHMR. 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.

Two deeper layers of surface hoar from December 13th and December 7th may still be found down 100-150 cm. The Dec 7th weak layer consists of a combination of decomposing surface hoar with a crust and faceted snow. Avalanche activity on these persistent weak layers has dwindled in the last week, with snowpack tests results trending to resistant and unreactive. 

The lower snowpack is characterized by a notable rain crust from early November that is surrounded by a weak layer of sugary facets. It may still be possible to trigger with large loads in steep, shallow, rocky areas with a thin to thick snowpack.

• Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
• Large cornice falls are dangerous on their own.
• If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.