Avalanche Forecast
North Columbia
New snow is on the way which is GREAT, but a buried weak layer down 30 to 70 cm continues to produce large human triggered avalanches. The message may be getting repetitive, but conservative terrain selection remains a must.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Caution with open slopes and convex rolls below treeline where buried surface hoar may be preserved.
- Numerous large avalanches have run on these layers in well supported, treed terrain.
- Conservative terrain selection remains prudent in this time of change.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
A few cm of snow Tuesday night and then a few more cm late Wednesday will rest on a potpourri of old surfaces including crust and feathery surface hoar. Storm slabs should be small Wednesday, but by Thursday they could pack more of a punch.
Travel and Terrain Advice
- Carefully monitor the bond between the new snow and old surface, touchy slabs may form quickly.
- Sluffs will be easy to trigger in steep terrain that is sheltered from the wind
- Watch for rapidly changing conditions during periods of heavy loading from new snow, wind, or rain.
Avalanche Summary
On Monday the early January interface continued to produce both natural and human triggered avalanches to size 2.5 on a variety of aspects above 1700 m. Crown depths were 30 to 75 cm and a size 1.5 avalanche was triggered by a skier on a north facing slope with a 22 to 32 degree incline.
On Sunday there was a widespread natural avalanche cycle to size 3.5. These very large avalanches were running on southwest, south and southeast facing alpine features and were triggered by a combination of above freezing alpine temperatures and direct solar input. There was one report of a size 1.5 human triggered avalanche failing on the mid-December interface on a south facing slope at 1100 m. A second human triggered avalanche was reported from a gently inclined slope at 2100 m, aspect unknown. The size 2.5 avalanche ran on the early January weak layer.
On Saturday natural avalanches to size 3 were reported on northwest though south facing terrain between 1800 m and 2700 m.
Snowpack Summary
Spotty freezing rain Monday may have left a slight "glaze" on the surface which adds to the crust that is being widely reported from many locations, high elevation north is likely one of the few crust-free zones. Fresh surface hoar 3 to 10 mm in size has been reported to at least 2100 m, possibly higher. We can probably expect a touchy storm slab to form on this interface as storm totals exceed 10 cm.
This snowpack is currently quite complex; there are two active Persistent Weak Layers (PWL) that we are monitoring.
The first PWL is known as the early January interface, it is 30 to 70 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 second PWL is the mid-December facet/surface hoar/crust combination that is now buried 60 to 140 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 90 to 200 cm is thought to have gone dormant for the time being.
Weather Forecast
On Wednesday morning a strong winter storm will arrive on the BC coast. Rather warm air and precipitation is expected to spread into the interior Wednesday afternoon resulting in snowfall through Thursday evening. The freezing level should fall back towards valley bottom Thursday night. Friday and Saturday look cool and calm with another system set to move into the interior on Sunday.
WEDNESDAY: Broken cloud cover, freezing level rising to around 1000 m, moderate south/southwest wind, 2 to 6 cm of snow possible in the afternoon, 5 to 15 cm possible Wednesday night.
THURSDAY: Broken cloud cover, freezing level around 1500 m, moderate to strong southwest wind, 1 to 5 cm of snow possible.
FRIDAY: Scattered cloud cover, freezing level beginning at valley bottom rising to around 1200 m in the afternoon, light southwest wind, trace of snow possible.
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As new snow begins to fall we can't forget about the persistent weak layers lurking in our snowpack that continue to produce large human triggered avalanches. Keep the terrain choices reigned in as the snowpack adjusts to the new load.