Avalanche Forecast

Issued: Jan 29th, 2021 4:00PM

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

Avalanche Canada cmortenson, Avalanche Canada

Recent 15-30 cm of low density snow will easily be transported by forecast moderate southwest wind. Chose conservative terrain where the wind is actively transporting snow and building wind slabs, which will be touchy anywhere they sit on top of a slippery surface hoar layer. 

Summary

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region. Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

Active weather brings light to moderate snow across the region with increasing winds and warmer temperatures. Higher precipitation amounts and freezing levels forecast for southern region.

Friday night: Mainly cloudy with clear periods and isolated flurries, trace to 2 cm new snow, light to moderate southwest ridge wind and alpine low temperature around -11C.

Saturday: Cloudy with clear breaks and isolated flurries, trace to 5 cm of new snow, moderate southwest ridge wind and alpine high temperatures around -7C. Late afternoon, wind will increase to strong as a warm front arrives and snow flurries will grow heavier with an additional 5 to 10 cm forecast overnight.  

Sunday: Cloudy with snow, 5-15 cm of new snow, light south ridge wind gusting strong in the alpine, alpine high temperatures around -5C and freezing levels 800 m - 1000 m.

Monday: Heavy snow, 10-25 cm of new snow, light south ridge wind gusting strong, alpine high temperatures around -4C and freezing levels 700 m - 1400 m.

Avalanche Summary

Minimal new avalanches have been reported on Friday, although data sources are limited. A MIN from near Kicking Horse 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. This is a great "heads up", they suggest, for what will happen on Saturday as winds increase.

On Thursday in the Golden area, about 10 cm of new snow coupled with easterly wind led to the formation of small but reactive new wind slabs and cornice growth. Farther south from the mountains east of Kimberlyl this MIN reports 20-30 cm of new snow that rested on a firm wind/sun crust. We're still lacking observations from elsewhere in the region, but it's safe to assume similar, if not more dangerous conditions exist in other areas with similar or greater new snow accumulations.

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.

Snowpack Summary

15 to 30 cm of new snow accumulated in the region by Friday, with heavier amounts the higher western mountains. This new snow has 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.

Terrain and Travel

  • 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.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Problems

Storm Slabs

An icon showing Storm Slabs

15-30 cm of new snow has accumulated in the region by Friday, making for a tricky regional variation in avalanche problems. In higher snowfall areas to the west of the region, more widespread storm slabs are likely forming over a weak layer of surface hoar that is widespread in sheltered areas. Expect touchy surface instabilities limited to wind loaded pockets in lower snowfall areas. 

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

A weak layer of surface hoar buried Jan 11 is down 30-60 cm and may be found on sheltered slopes near treeline in northern parts of the region. Deeper layers from early December and November can still be found in the snowpack and remain a cause for concern in thick to thin areas at upper elevations. Concern for all of these layers is increasing as they adjust to a new load of snow. Steep, rocky and shallow snowpack areas would be likely trigger areas.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3.5

Valid until: Jan 30th, 2021 4:00PM