Avalanche Forecast
South Columbia
The snowpack is complex and there are many unanswered questions. Three active weak layers remain sensitive to human triggering. The easy solution is to choose simple terrain free of overhead hazard as the snowpack adjusts.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- The new snow will require several days to settle and stabilize.
- Carefully investigate the bond of the new snow before stepping out into more challenging terrain.
- Be very cautious as you transition into wind affected terrain, wind slabs may be deep and touchy.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
The riding conditions may be great, but we can't forget about the persistent weak layers lurking in our snowpack that remain quite capable of producing very large avalanches. Keep the terrain choices reined in as the snowpack adjusts to the new load.
Travel and Terrain Advice
- Good day to make conservative terrain choices and watch for clues of instability.
- Storm slabs in motion may step down producing large destructive avalanches.
- Numerous large avalanches have run on these layers in well supported, treed terrain.
Avalanche Summary
On Wednesday wind slab avalanches to size 1.5 were human triggered on northwest, north and northeast facing features between 2000 m and 2150 m. A size 2.0 persistent slab avalanche was human triggered on a northeast facing feature at 2200 m, this slab failed on the early January weak layer. There was also a natural size 2.5 glide crack failure on a southeast/east facing feature at 1600 m. Bear in mind that this activity occurred before the storm.
Tuesday was much more quiet. Explosive control work produced cornice failures to size 2 on north and northeast facing ridge lines. A "tree bomb" initiated a size 1.5 persistent slab avalanche on an east facing feature at 2200 m.
On Monday warm temperatures and direct solar induced natural avalanches to size 3.0 on solar aspects, the largest ran on a steep south/southwest face in the alpine. Human triggered avalanches to size 1.5 were reported on north and northeast facing terrain above 2000 m, likely running on the early January interface.
Snowpack Summary
The current snowpack is complex, we now have three active Persistent Weak Layers (PWL) that we are monitoring.
Wednesday and Thursday's highly convective storm left 10 to 25 cm in its wake. This snow buried the mid-January PWL which is a crust and/or surface hoar interface. Prior to Wednesday's storm the crust was reportedly widespread, high elevation north is likely one of the few crust-free zones. The now buried surface hoar is 4 to 20 mm in size and was present to at least 2100 m, possibly higher.
The second PWL is known as the early January interface, it is 40 to 80 cm below the surface. It is composed of surface hoar on sheltered slopes as well as sun crust on steep solar aspects and is present at all elevation bands. Recent snowpack tests have shown sudden results with moderate loads.
The third PWL is the mid-December facet/surface hoar/crust combination that is now buried 70 to 150 cm deep and is most problematic at and below treeline. This interface is not thought to be present in the alpine.
The November rain crust down 150 to 200 cm is thought to have gone dormant for the time being.
Weather Forecast
The low that recently delivered significant wind, snow and rain to the interior is expected to weaken on Friday resulting in less frequent and less intense convective flurries. Saturday offers a brief lull in the action before another system takes aim at the interior Sunday.
FRIDAY: Overcast, freezing level beginning at valley bottom rising to around 900 m in the afternoon, moderate west/southwest wind, 5 to 10 cm of snow possible.
SATURDAY: Overcast, freezing level beginning at valley bottom rising to around 1000 m in the afternoon, light to moderate west/southwest wind, 1 to 5 cm of snow possible.
SUNDAY: Overcast, freezing level beginning at valley bottom rising to around 1000 m in the afternoon, moderate to strong southwest wind, 5 to 15 cm of snow possible.
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By Friday a slab 10 to 30 cm in depth will rest on a nasty combination of crust and surface hoar. The slab will be much deeper in wind exposed features and is expected to remain quite sensitive to human triggering.