From rag + -y, rag being a dialectal (northern England) word for a fog or mist with drizzling rain, related to dialectal Danish rag (“sea vapour”). Compare roke, rawk, from a word for smoke (compare Swedish rök (“smoke”)), which may or may not be related.
Meanings
(Yorkshire, dialectal, especially, obsolete, possibly, qualifier:Lancashire) Foggy, misty (and typically cold), with drizzling rain.
It looks a bit rough wi' lyin' out thoose raggy neets. 1874 (edition of 1879), Waugh, Chim. Corner, page 157
It's been nobbut raggy weather up o' the moors this winter. 1892, David Grieve, Ward, III, book IV, vi:
raggy en · NOUN · etymology 3
Meanings
(alt-of, alternative, uncountable) Alternative form of ragi (“finger millet”).