North Rockies

New snow, extreme winds, and rising temperatures will be the obvious components of avalanche danger during the oncoming storms. Deeply buried, reactive weak layers make the potential consequences of triggering an avalanche even higher. It's a good time to avoid avalanche terrain.

SATURDAY NIGHT: Cloudy with flurries bringing 5-15 cm of new snow. Strong southwest winds.

SUNDAY: Cloudy with continuing flurries bringing about another 5 cm of new snow, totalling 10-20 cm including overnight amounts, continuing overnight again. Strong to extreme southwest winds, easing only a bit overnight. Alpine high temperatures reaching about -2 as freezing levels jump to around 1700 metres.

MONDAY: Cloudy with continuing flurries bringing another 5-10 cm of new snow and 2-day snow totals to 20-30cm. Moderate to strong west winds. Alpine temperatures falling from about -7 to -12 over the day as freezing levels return to 1000 metres.

TUESDAY: Cloudy with flurries bringing about another 5 cm of new snow. Strong southwest winds. Alpine high temperatures around -10.

The North Rockies field team spent the day in Renshaw on Friday. Although visibility was limited, they were able to report evidence of at least one large (size 2) natural avalanche that ran in steep treeline terrain. It is suspected to have run on one of the mid-snowpack persistent weak layers described in our snowpack summary, found about 80-110 cm deep in this area. 

Saturday's improved visibility may bring similar reports of recent activity. Forecast new snow, wind, and warming ensure Sunday will be another active day for avalanches.

We have quite a few more recent reports of very concerning persistent slab avalanche activity in the region. This spooky report of large remote triggered avalanches came in Wednesday.

Widespread whumphing was reported Tuesday which is a clear sign of an unstable snowpack. More details in this MIN report.

There was likely a widespread natural avalanche cycle on Sunday and Monday as a result of heavy loading from snow and wind. We received numerous reports of touchy conditions as evidenced here and here. 

There was a fatal avalanche accident in the Hasler area last Saturday. The incident occurred on a northeast aspect between 1400 and 1600 m. The avalanche was a size 2.5. The fracture line was estimated to be 50-100 cm and is suspected to have been a persistent slab avalanche running on the late January weak layer of surface hoar described in our snowpack summary. Click here to link to a report on the incident.

Up to about 20 cm of new snow is expected to accumulate in the region by the end of the day on Sunday, with distribution that should be a bit more uniform than we saw with our last storm pulse, which brought about 30 cm to the south of the region and very little to the north.

These variable recent accumulations added to a previously wind-affected 40-60 cm of storm snow that fell through last weekend. This snow significantly increased the load overlying a couple of weak layers of faceted snow (and potentially surface hoar) from early and mid February, as well as another especially problematic, slightly deeper, widespread persistent weak layer from late January that consists of surface hoar. This layer is likely 80-120 cm deep near Renshaw and 60-100 cm deep around Torpy and further north.

Reports suggest this layer is most prevalent around treeline elevations, but likely reaches into the alpine and in openings below treeline too. It may sit above a crust below 1600 m. The likelihood of triggering this layer will likely to continue to increase under incremental loading from forecast snowfall. The consequences of triggering it are high.

• Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
• Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.