Avalanche Forecast

Monday night: Mostly clear, light variable winds, alpine temperatures near -13 C.

Tuesday: Increasing cloud, scattered flurries moving in overnight with up to 5 cm of accumulation, winds shift to the southwest and increase to strong, alpine high temperatures around -7 C.

Wednesday: Partly cloudy, light west winds, alpine high temperatures near -12 C.

Thursday: Mix of sun and cloud, light northeast winds, alpine high temperatures -14 C. 

Strong winds on Tuesday are expected to continue to build wind slabs that may be possible to human trigger in leeward features. On Sunday, operators in neighboring Glacier National Park reported a large (size 2) wind slab releasing naturally in the storm snow on a north aspect. Cornices may be reaching their breaking point and can act as triggers on slopes below. 

There is uncertainty as to the distribution and sensitivity of a weak layer buried Jan 11th in the region. This MIN from Clemina Creek over the weekend reports that the Jan 11th surface hoar was cracking and propagating in sheltered treeline and below treeline areas where it was buried 40-50 cm deep.

An extensive natural avalanche cycle occurred during last week's storm as up to 70 cm of new snow blanketed the region and was subsequently redistributed by strong winds. Several of these avalanches were thought to have stepped down to deeper layers (see this MIN report from the Gorge area for an example). Avalanches breaking in the recent snow have the potential to step down to deeper layers, creating larger and more destructive avalanches. 

Since field observations in this region are limited, please consider submitting your observations to the Mountain Information Network. 

Recent snow accumulations ranging from 10-25 cm are being redistributed by variable winds. Winds switched direction from the southwest to the northwest, creating a tricky wind-loading pattern at upper elevations. Winds are forecast to shift back to the southwest and to increase on Tuesday, keeping wind slabs on lee features as a primary concern. Ongoing snow and wind over the past week have contributed to notable cornice growth.  

50-70 cm of snow from the past week has buried a weak of layer of surface hoar that has shown reactivity in the north of the region. This persistent weak layer is more likely to be preserved in sheltered, open slopes at and below treeline.

A couple of older persistent weak layers exist in the mid to lower snowpack. The distribution of these layers is variable, but they follow a similar pattern to the layer discussed above. The upper layer from late December, down about 100-140 cm, consists of spotty surface hoar at shaded treeline and below treeline elevations. The lower layer from early December buried 150-200 cm deep consists of a combination of decomposing surface hoar with a crust and faceted snow. Snowpack tests on these layers show increasingly resistant results. The lower layer is now largely unreactive, but remains a prominent snowpack feature.

• Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
• Be aware of highly variable recent wind loading patterns.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Avoid exposure to slopes that have cornices overhead.