By Ian Currie - Editor of Weather Eye magazine, for all fascinated by our weather.
Average May maximum temperatures across the UK such as Birmingham, York, Cardiff and London average between 16C to 18C though in the northern Isles of Scotland at Lerwick a chillier 12C so certainly a vest needed here. At night temperature values drop to around 8C in London but more like 6C in Edinburgh.
The month of May is also associated with the Hawthorn or May tree and its familiar white flowers. The word hawthorn comes from the old English haga meaning enclosure as the hawthorn is used for hedging and its flowers are synonymous with the coming of summer. It was thought to ward off evil and was hung about doors and windows.
The average date of its flowering is just after the first week in the south of England and near to the middle of the month in the Midlands northwards. This date over the past 30 years or so is getting earlier and nowadays it is becoming increasingly common for it to blossom in April. For most places after the middle of May there is a much reduced risk of an air frost. So for most places damaging frost is much less likely after the middle of May and at my Surrey weather station I have not recorded an air frost during the second half of the month in 36 years of records.
However sharp air frosts have occurred even late in the month. May is a sensitive time of year with so much young growth and harsh frosts can do great damage such as in 1941 when the temperature dropped to minus 9C in Norfolk.
At the well known frost hollow at Rickmansworth in Hertfordshire minus 4.4C was recorded as late as the 29th during 1936. The previous year it measured minus 8.3C on the 17th May and other prone areas such as Braemar in the Dee valley within the Highlands and the valleys in Clwyd, west of Denbigh in north Wales have experienced minus 5C or below during the last few days of May.
The lines from F K Robertson’s Whitby Gazette of 1855 spring to mind when cool weather occurs during the month:,
The wind at North and East
Was never good for man nor beast
So never think to cast a clout
Until the month of May be out.
So to be really safe wait until June.
There is one last definition to our May saying. It concerned an apocryphal 18th century lady of ill repute nicknamed `Lady May' who was often arrested in November when it became cold and spent the rest of the winter incarcerated out of the weather. She inveigled herself out of jail when it turned warmer in May. The expression arose `Don't cast a clout 'til Lady May be out'.
Metcheck would like to thank Ian Currie for contributing this article to our blog and recommend taking a look at www.frostedearth.com, a fantastic resource for all weather enthusiasts.