Avalanche Forecast
South 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
- 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 both natural and human triggered avalanches to size 1.5 were triggered on north and northeast facing slopes above 1700 m. A rather spooky size 2.5 avalanche was triggered by a professional releasing a cornice onto a north facing slope at 1900 m.
Reports from the north of the region on Wednesday included an observation of a size 2.5 wind slab triggering remotely from 300 metres away on a low angle slope at 2300 metres. Elsewhere, storm slabs were observed running naturally and with explosives from size 1.5-3. South aspects were especially active where solar warming served as a trigger.
Explosives control in the adjacent North Columbias yielded numerous persistent Slab results from size 2-3.5 on all aspects at all elevations. The deep mid-December layer and an even deeper layer from November were both frequent failure planes. The mid December layer is also suspected in two natural size 4 releases in and near the Glacier National Park area.
Snowpack Summary
20 to 30 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.
Three active weak layers are now quite deep in our snowpack:
1) 70 to 140 cm of 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 130 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.
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. While the epicenter of this engagement is north of the region, 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 don't bet the house on them.
(FRIDAY: 15 to 40 cm, strong west wind.)
FRIDAY NIGHT: Freezing level around 1300 m, strong west/northwest wind, 10 to 35 cm of snow.
SATURDAY: Overcast, freezing level rising to around 1500 m, moderate to strong west/northwest wind, 15 to 30 cm of snow.
SUNDAY: Overcast, freezing level rising to around 1500 m, moderate to strong west/southwest wind, 5 to 15 cm of snow.
MONDAY: Scattered cloud cover, freezing level at valley bottom, light to moderate northwest wind, 1 to 5 cm of snow.
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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.