A significant avalanche cycle is underway with large, destructive avalanches running full path observed every day this week. Overhead hazard is significant, so even travel below the treeline should avoid avalanche runout zones. Ice climbers avoid exposure to overhead avalanche terrain. With the onset of arctic air, we expect the natural activity to taper, but human triggering will remain almost certain on Wednesday.
80 cm of recent snow with consistent strong SW/W wind continues to build slabs. Use caution in all lee areas with wind effect and watch for wind loading occurring above you. These avalanches may start small, but have the potential to step down to the deeper weak layers and create large avalanches.
Slabs 80-120 cm deep overlie three persistent weak layers formed in January which are a mix of crusts on solar aspect, facets on northerly aspects and isolated surface hoar. These avalanches could also step down to the Nov facets and become even larger.
Facets and depth hoar at the bottom of the snowpack provide weak support for the entire snowpack. Incremental snowfall since the start of February has brought the overlying slab to the tipping point and we have started to see large, destructive avalanches failing on the November facets and running a long distance.
Natural avalanches up to size 4 have been observed in the past 48 hours, including multiple size 3 and 3.5 avalanches in Kootenay and Yoho parks on Tuesday. Numa Peak, Mt. Dennis, Mt. Field, and Mt Burgess all had size 3 natural avalanches on Tuesday. We expect the natural avalanche cycle to taper with the onset of arctic air, but human triggering will remain almost certain for Wednesday.
The five-day storm snow totals are Simpson 81cm, Sunshine 60cm, Stanley 38cm, Bosworth 69cm and Bow Summit 23cm. All of this fell accompanied by strong winds, creating an unstable snowpack across the region. Natural and explosive-triggered avalanches have been widespread, some running full path, with slab avalanches failing in the storm snow, crusts in the upper meter and deep avalanches on the ground. Natural activity should taper with the onset of cold temperatures, but human triggering remains almost certain.
The storm has ended and an arctic air mass has arrived. Wednesday and Thursday will reach lows of -25 to -30 with light snow and gusty east winds. Not your typical bluebird cold snap - this one looks nasty with swirling winds and frigid temps. The good news is that it's short-lived as warmer air returns on Friday.
More details can be found in the Mountain Weather Forecast.
