Public Observation #2021-508

Submitted:
December 21, 2021 8:56 PM
Observation Date:
December 21, 2021
Zone or Region:
Central Cascades
Activity:
Skiing/Snowboarding
Location:
Sw century carpoolers
Did you observe any avalanches? 
Yes
Avalanche Type:
Soft Slab
Size:
D2: Could bury, injure, or kill a person
Elevation:
Aspect:
SE
Comments:
9600 feet. Lower lewis..south sister..natural slide most likely sometime on Monday?
Did you see shooting cracks? 
Yes
Did you experience collapsing or whumpfing? 
No
Riding around roads end of century.
Sunday was wet.. but it got colder and switched to snow come afternoon..storm intensified that night and went thru Monday day; and deposited roughly 10 to 18 inches in terrain above 6500k. Snow was wet Monday upon leaving but last night's cold air did the trick..when visibility broke today, we saw an impressive natural slide on South sister on the lower lewis glacier headwall. From a distance it looked like it slide 600 feet across and was probably d2 in size. This is a east, southeast aspect around 9600k that gets wind loaded and forms a cornice typically.
Saw evidence of a potential four inch windslab above the treeline on higher Alpine slopes (7800feet and above), but triggering seemed difficult. Most elevations you could feel this new storm snow fell on a thinner breakable rain crust from the Saturday event. Bonding seemed good and pack below treeline seemed very well bonded and right side up.
Sorryy for the spelling...