ne'er cast a clout till May be out
Etymology
Ne’er is a contraction of never; while clout is an archaic or dialectal word for a (worthless) piece of cloth or a rag, and is used to refer to clothing in a derogatory manner.
Proverb
ne'er cast a clout till May be out
(UK, dialectal) Do not change from winter clothes to summer clothes until June, as there is often a sudden cold snap in May.