Watch for fresh wind slabs in upper elevation terrain. Natural persistent slab activity has slowed way down, but large avalanches may still be sensitive to human triggering. If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.
A bit of new snow and wind out of both the southwest and northwest Thursday night into Friday is likely to form fresh wind slabs in exposed terrain features.
All of the old storm snow is slowly settling into a slab which rests on weak surface hoar 100 to 160 cm below the surface. Natural avalanche activity has waned, but human triggering may still be possible, especially in more challenging/complex terrain. This isn't the kind of avalanche problem you can feel under your skis, track or feet, it's far too deep for that. The answer lies in terrain selection.
The North Columbias received upwards of 80 cm from last weekend's big storm which is slowly settling into a slab. There is now a great deal of uncertainty as to how quickly the snowpack is regaining strength. Anywhere from 100 to 160 cm of snow is now resting on a widespread layer of large, feathery, surface hoar which we're calling the "December 11th Surface Hoar." Activity on this interface has really tapered off, but this layer produced some very large natural avalanches during and just after the storm.
A combination of surface hoar, crust & facets formed in late November is now over 170 cm deep. This layer is likely trending toward dormancy.
It’s mostly dribs and drabs of snow for the next few days with increased wind in the higher alpine terrain features. A bigger storm is on the horizon as we enter the New Year.
THURSDAY NIGHT: Freezing level at valley bottom, moderate to strong south/southwest wind in the alpine, potential for 4 to 12 cm by Friday morning.
FRIDAY: Overcast, freezing level at valley bottom, light variable wind at most elevations, moderate to strong northwest wind in high elevation alpine terrain, 1 to 5 cm of snow possible during the day.
SATURDAY: Broken cloud cover, freezing level at valley bottom, light variable wind at most elevations, moderate to strong west/northwest wind in high elevation alpine terrain, no significant precipitation expected.
SUNDAY: Scattered cloud cover, freezing level at valley bottom, light variable wind, no significant precipitation expected.
On Wednesday control work produced some size 2.5 persistent slab avalanches on both north and south facing features between 2100 and 2400 m, crowns were up to 120 cm in depth. Natural avalanches size 2.5 to 3 were also observed in the neighboring Glacier National Park in steep terrain, these avalanches were running to the top or middle of runnouts.
Avalanche activity has really tapered off, but avalanches during and just after the storm were spectacularly large and destructive. On Tuesday some natural avalanches up to size 2 were observed in ridge top start zones on a northwest facing slope around 2100 m. There were also some rather spooky size 2 storm slabs on east/southeast facing slopes down in the trees at 1900 m. On Monday natural avalanche activity from size 2 to 3 was observed on a variety of aspects above 2100 m. Control work produced avalanches from size 2 to 4 that involved all elevation bands, some mature timber was taken out by very large avalanches.
