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RegisterFeb 22nd, 2021–Feb 23rd, 2021
North Columbia.
As we head into a couple days of friendlier weather, resist the allure of bigger terrain and be especially wary of recently wind loaded features. Recent storm snow sits on a thick layer of weak, sugary facets and bonding at this interface may take some time.
MONDAY NIGHT: 5-15 cm new snow, northwest wind easing strong to moderate, freezing level dropping from 1500 m to valley bottom.
TUESDAY: Scattered flurries with sunny periods, light northwest wind, freezing level 800 m.
WEDNESDAY: Mix of sun and cloud, light to moderate southwest wind, freezing level 1000 m.
THURSDAY: 10-15 cm of new snow, moderate to strong southwest wind, freezing level 1000 m.
Reports from the highway corridor on Monday include explosive triggered storm slabs size 2-3, natural storm slabs size 1.5-2 on NW aspects and loose wet size 1 below 1000 m. We suspect that reports of more widespread natural activity will start to come in as the weather clears and visibility improves.
Last week, older winds slabs in cross and reverse-loaded terrain features surprised a number of skiers, triggering avalanches up to size 2.5.
Persistent slab avalanche activity has dwindled since the beginning of February but a conservative approach is critical as this storm begins to add weight to it. This old MIN report from Joss Mountain is a helpful example of the lower elevation slopes where the surface hoar has been preserved and may reactivate this weekend. This old MIN report from the Gorge is a helpful example of the lower elevation slopes where the surface hoar has been preserved and may see a resurgence of reactivity in the storm.
40-80 cm of recent snow has likely been blown around by strong to extreme westerly winds, forming thick, reactive slabs in lee features at upper elevations. At lower elevations, the new snow is likely settling and gaining slab property in the mild temperatures.
The recent snow sits on old, facetted and/or extensively wind affected snow that sat on the surface during the extended cold, windy drought period. There is uncertainty around how long it will take for this interface to bond.
We've now got 70 to 120 cm of snow above the late January persistent weak layer which is composed of surface hoar in openings in the trees and/ or a crust on steep solar aspects. We are awaiting reports of avalanche activity during the storm, specifically whether they indicate step- downs to this layer, to determine whether or not it continues to be a problem.