A "blue norther" will lead to huge temperature drops this weekend. But what does the "blue" part mean, anyway?

As a cloud comes out from behind the dark clouds into a bright blue sky, it is edged with a silvery lining. Thus we are moving from relative darkness into bright light and the meaning of the idiom ...

The seven BE-4 engines roared — sending awed spectators into screams and cheers — as Blue Origin's New Glenn rocket ascended ...