Avalanche Forecast
North Columbia
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
- Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
- Avalanche hazard is expected to continue to increase Saturday, think carefully about your egress.
- Stick to simple terrain features and be certain your location isn't threatened by overhead hazard.
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
- You need to anticipate very large and destructive full path avalanches as you craft travel plans.
- Uncertainty is best managed through conservative terrain choices at this time.
- Storm slabs in motion are likely to step down and initiate very large avalanches.
Avalanche Summary
On Thursday explosive control work produced avalanches to size 3.5 on a variety of aspects above 2100 m. Failure planes included mid-January, mid-December and late-November. Natural avalanches to size 2 were observed on east facing slopes near 1900 m.
Wednesday included further observations of recent activity showing storm slabs releasing naturally, from size 2 to 3, on all aspects and elevations. South aspects were especially active where solar warming served as a trigger. Explosive control also yielded numerous persistent slab results from size 2 to 3.5 on all aspects/elevations. All our persistent weak layers of concern were active, with the possible exception of the early January layer. The mid-December layer is also suspected in two natural size 4 releases in and near the Glacier National Park area.
On Tuesday, natural avalanche activity was widespread, running on all aspects and elevations. Storm and wind slabs reached size 3 while persistent slab avalanches failing on the mid-December layer ran to size 3.5. A size 2.5 avalanche on a northeast facing slope at 1920 m resulted in a single fatality. More details are available here.
Snowpack Summary
20 to 50 cm of new snow fell Thursday and Friday. This rests on up to a meter of new snow that fell last week which has settled into a slab aided by a warming event on Monday the 29th and strong to extreme southerly winds on January 29th and 30th.
Four active weak layers are now quite deep in our snowpack:
1) 80 to 160 cm of storm snow sits on a crust and/or surface hoar layer from mid-January. The crust is reportedly widespread, with the possible exception of high elevation north aspects. The mid-January surface hoar is 5 to 20 mm in size and was reported at tree line elevations and possibly higher.
2) Deeper in the snowpack, the early-January persistent weak layer is 150 to 175 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is found at all elevation bands.
3) Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried up to 200 cm below the surface. It is most problematic at and below tree line.
4) A crust/facet layer from late November is yet another failure plane responsible for very large recent avalanches.
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 the weekend. 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 do not bet the house on them.
(FRIDAY: 10 to 30 cm, strong west wind)
FRIDAY NIGHT: Freezing level around 1300 m, strong west/northwest wind, 15 to 40 cm of snow.
SATURDAY: Overcast, clearing in the evening, freezing level at valley bottom, moderate to strong west/northwest wind, 10 to 20 cm of snow.
SUNDAY: Overcast, freezing level at valley bottom, light to moderate west/southwest wind, 5 to 15 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.