Avalanche Forecast
Cariboos
Intense snowfall and strong wind will almost certainly initiate a very large and destructive natural avalanche cycle on Saturday. Only the most simple avalanche terrain free of overhead hazard is appropriate at this time.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Stick to simple terrain features and be certain your location isn't threatened by overhead hazard.
- Avalanche hazard is expected to continue to increase Saturday, think carefully about your egress.
- Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Several deeply buried weak layers are persisting in the snowpack and continue to produce very large avalanches, especially with heavy triggers. This is a time to carefully measure your exposure to avalanche terrain and to avoid overhead hazards.
Travel and Terrain Advice
- Storm slabs in motion are likely to step down and initiate very large avalanches.
- Uncertainty is best managed through conservative terrain choices at this time.
- You need to anticipate very large and destructive full path avalanches as you craft travel plans.
Avalanche Summary
On Thursday explosive control work produced avalanches to size 2.5 failing on both the mid and early January interfaces. These avalanches ran on north, northeast, east and southeast facing features between 1600 and 2600 m. A cornice failure resulted in a size 2 wind slab avalanche on a steep north facing terrain feature at 2100 m.
Reports from Wednesday included more observations of widespread natural activity that took place over the previous few days. Numerous recent size 2-3 releases were observed on all aspects at all elevations and several avalanches reached size 4. Subsequent explosives control yielded storm slab and wind slab releases from size 2-2.5 and persistent slab results generally from size 2.5-3. The early January persistent weak layer was named as the primary failure plane for persistent slab releases, although several larger releases stepped down to the mid-December layer.
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.
Snowpack Summary
25-50 cm of storm snow fell between Sunday and Tuesday night. Temperatures reached -2 C at treeline in the south of the region (and +2 C near Barkerville) on Monday afternoon. The new snow sits on an unstable snowpack with three active weak layers we are monitoring:
1) Down about 40-80 cm is a crust and/or surface hoar layer that was buried in mid-January. The surface hoar is up to 10 mm in size, found at all elevation bands and has been very reactive on north through east aspects between 1900-2600 m.
2) Deeper in the snowpack, the early-January persistent weak layer is found 50 to 100 cm below the surface. This layer has been reported as the most active persistent weak layer during a recent natural avalanche cycle that took place in the region. It has also been the most reactive to recent explosives control.
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. Many avalanches that failed at shallower weak layers 'stepped down' to this interface during the recent avalanche cycle and in recent explosives control.
Weather Forecast
The provincial weather pattern features a clash of titans as juicy warm air streams into the northern interior and then smashes into a rather bullish Arctic front. The Cariboos and North Columbias are expected to see the most action from this engagement, strong snow and wind are expected through Friday night before a brief drying trend takes hold Saturday. We know that weather models do not capture these kinds of events well, there could be more snow and wind than forecast, and there is increased potential for very heavy snowfall locally. Take the following ranges as a suggestion, but don't bet the house on them.
(FRIDAY: 15 to 30 cm, strong west wind)
FRIDAY NIGHT: Freezing level around 1300 m, strong west/northwest wind, 20 to 40 cm of snow.
SATURDAY: Overcast initially, clearing throughout the day, freezing level at valley bottom, strong northwest wind, 1 to 5 cm of snow possible in the morning.
SUNDAY: Overcast, freezing level at valley bottom, light to moderate west/southwest wind, 5 to 10 cm of snow possible.
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Uninterrupted heavy snowfall and strong wind will continue to add mass to the already robust and touchy storm slabs Saturday. Let's not overthink this scenario, we all need to retreat to simple terrain while the storm rages on.