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curdled sky is the same as
curdled sky is the same as buttermilk sky - that was one of the ways my grandfather watched for rain. Curdled/Buttermilk sky is usually altocumulus clouds -usually on a warm and humid summer morning & usually followed by thunderstorms. We dont have mackerels in this area so I guess that mackerel sky never became a catch phrase down in my neck of the woods.