Observation: Public
Observation Details
Name:
Gary BrillObservation Date:
February 24, 2021Submitted:
February 25, 2021Zone or Region:
East CentralActivity:
Skiing/SnowboardingLocation:
Blewett PassObserved Avalanches
Did you observe any avalanches?
YesAvalanche Type:
Hard SlabSize:
Size 3: Could bury and destroy a car, damage a truck, destroy a wood frame house, or break a few treesElevation:
5800-5400'Aspect:
NEComments:
This was the old avalanche I thought I saw two weeks ago, and despite recent snows and wind, the crown from 200 yards away still appeared to be about 2-1/2' thick. It began in a rocky area and presumably covered an entire bowl. The crown ran downslope along a ridge line for about 150 yards. Two more recent avalanches from the last storm were also visible; one rather small with likely a 12" crown from steep, rocky terrain, the second probably a Class 2 where the toe of the avalanche was still visible but the crown completely filled in.Signs of Unstable Snow
Observations
7" of surface snow was loose; the bond at lower elevations to a hard base layer fair with just about a cm or 2 of low to moderate density transition - this to about 5100', but with the hard layer gradually disappearing with altitude. Higher the bond appeared good with a good density profile in the top two feet or so where there was no evidence of recent windslab. In certain areas, possibly extensive, the windslab was up to 12-16" thick, probably 1F, and was largely unsupported with loose, Fist snow beneath for 5-10" inches. I never felt any sense of failure and tested one windroll by forcefully thrusting my skis and there was no failure. Nonetheless, with the poor structure beneath the windslab, and the possibility of buried surface hoar in protected areas, we avoided steep open slopes and gullies greater than about 32 degrees. The failure of either could have been catastrophic.
There was fresh surface hoar to 4-7mm on top of loose surface snow that likely did not ablate because there was almost no wind. The characteristic sheen of surface hoar could be widely seen well up into the higher elevations in this area.
Surface snow became moist with much sun exposure though we did not reach the ridgeline. Suncrust would be likely on solar aspects, especially with little wind yesterday.
I feel the bond to the hard layer would be suspect to whatever elevation it exists with much loading in coming storms. This latter observation may be pertinent along the east slopes of the Cascades away from the crest. The underlying snowpack at lower elevations is likely strong enough beneath the recent crust.