Avalanche Forecast

Issued: Jan 31st, 2018 5:55PM

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

ghelgeson, Avalanche Canada

Cariboos.

Take a cautious and curious approach to the mountains Thursday. We're on the heels of a large natural avalanche cycle, and we're uncertain as to how sensitive our deeply buried persistent weak layers are to human triggering.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain on Friday

Weather Forecast

Thursday is expected to be rather lackluster, but things get a lot more interesting as we head into the weekend. A rather bullish Arctic front is slowly moving south while a turbulent thrust of warm air is staging in the eastern Pacific. This clash of opposing systems should generate significant snow and wind, but the exact location and intensity is difficult if not impossible to pin down right now. The region could pick up 30 to 60 cm by Sunday evening. Stay tuned for more details. THURSDAY: Increasing cloud cover, freezing level at valley bottom, light to moderate southwest wind, trace of snow possible. FRIDAY: Overcast skies, freezing level at valley bottom, moderate to strong west/southwest wind, 10 to 20 cm of snow possible. SATURDAY: Overcast skies, freezing level at valley bottom, moderate to strong northwest wind, 10 to 20 cm of snow possible.

Avalanche Summary

On Tuesday natural avalanches to size 2.5 were reported on northwest facing slopes at 2200 m, running on the early January interface. A size 2.5 avalanche on a northeast facing slope at 1920 m resulted in a single fatality in Clemina Creek. More details available here. A natural storm slab avalanche cycle occurred on Monday with heavy snow and temperatures up to +2 C in some tree line locations. See this MIN report for a good example of the avalanche activity.

Snowpack Summary

25 to 50 cm of storm snow fell between Sunday and Tuesday night. Temperatures spiked to -2 C at tree line in the south of the region (and +2 C near Barkerville) on Monday afternoon. The new snow sits on a complex snowpack and there are three active weak layers we are monitoring:1) Down about 40-80 cm is a crust and/or surface hoar layer buried mid-January. The surface hoar is up to 10 mm in size, found at all elevation bands and very reactive on north east aspects between 1900-2600m.2) Deeper in the snowpack, the early-January persistent weak layer is found 50 to 100 cm below the surface. 3) Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 100 to 150 cm deep. It has been most problematic at and below tree line.See here for a good summary of snowpack test results.

Problems

Storm Slabs

Natural activity will likely diminish Thursday, but human triggered avalanches remain a concern. With all the recent storm snow, avalanches in motion could entrain significant mass, especially in bigger terrain features and avalanche paths.

The new snow could use a bit of time to settle and stabilize.Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.Caution with wind slabs, especially in steep unsupported and/or convex terrain features.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1.5 - 2.5

Persistent Slabs

As we move out of a storm and avalanche cycle there is a lot of uncertainty surrounding the triggerability of our deeply buried persistent weak layers. When we don't know, we have to scale our terrain choices accordingly.

Uncertainty is best managed through conservative terrain choices at this time.Storm slab avalanches have potential to step down and produce very large destructive avalanches.If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2.5 - 4

Valid until: Feb 1st, 2018 2:00PM