The timing and intensity of solar radiation on Friday is uncertain. If the sun makes an appearance, the snowpack could destabilize quickly and the Avalanche Danger may be HIGH.
Summary
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Friday
Weather Forecast
A ridge of high pressure will keep the region mainly dry and sunny for the early part of Friday. Over the weekend a series of frontal systems will make their way across the region bringing 5-15cm of new snow each day. Ridgetop winds will be light on Friday, increasing to moderate and southwesterly for the weekend. Freezing levels will hover around 1500m on Friday, climb to about 1800m on Saturday, and then drop to about 1500m by Sunday.
Avalanche Summary
At the beginning of the week, several slab avalanches were noted on solar aspects in recent storm snow, including one very large size 3 that started on a hanging convex feature at 2400 m and ran all the way to valley bottom. Most of these avalanches appeared to be initiating in a layer of surface hoar buried on February 27. On Wednesday another naturally triggered persistent slab avalanche was observed failing on the February 27th surface hoar. It started as a size 2.5 slab on an east aspect at 2600m and ran to valley bottom (triggering other slabs to size 3 en route). On Sunday, there was a fatal avalanche near Sicamous that occurred on a north aspect at 2025 m that most likely ran on the Feb-27 surface hoar layer. I'm sure there was a good round of wind/storm slab activity in response to new snow and strong winds on Thursday. I also expect ongoing potential for human triggering on Friday. Sun may also be the driver for avalanche activity on Friday. With that, you can add cornices and loose wet avalanches to the mix. Solar warming will also increase the likelihood of avalanches failing on deeper persistent layers.
Snowpack Summary
Snowfall accumulations on Thursday were in the 10-20cm range. Strong southerly winds redistributed these accumulations into touchy wind slabs at treeline and in the alpine. Approximately 70 cm below the surface lies a variable interface that comprises surface hoar, facets, a crust, or some combination of all three. This layer was buried on or around Feb-27 and has been very active since the weekend. I anticipate this layer will continue to be reactive to sled or skier traffic and/or additional loading from new snow. A previous surface hoar/crust layer buried Feb-10 is now down over a metre. This layer has become less likely to trigger, but continues to be discussed as a possible failure plane by commercial operations. Its presence keeps open the possibility of very large avalanches, as a small surface slide could step down into this deeper layer.
jlammers,
Avalanche Canada
