There are almost innumerable sites (ask Google) who will explain to you what “N’ere cast a clout till May is out” means. Just in case you’re wondering it means “Don’t put your warm underwear away until the weather warms up”.
Most explanations focus on the problem identifying May. Is it May the month, or is it May the blossom. A lot of people feel that waiting until June – i.e. the end of May is being a bit too cautious and anyway June 21st. is the northern hemisphere’s summer solstice, so if you’re still wearing your long-johns by then you might as well keep them on ready for next winter. The May blossom, on the other hand, often appears by the end of April (not this year though) and April showers can easily turn into nasty mean, vicious hail, sleet and snow storms.
That very nasty cold April wind is, at the moment, blowing around large clumps of cast off fleece. Many of the sheep are looking decidedly tatty as they shed their winter underwear in large handfuls against any hedge or fence they lean on.
They’ll be sorry! The May blossom, let alone May, isn’t out yet.