By Philip Eden
May began with a week of dry, sunny and rather warm weather, but thereafter there were several short unsettled spells with widespread rain and low temperatures. The mean sea-level pressure chart for May shows and low centre of 1008 mbar near the Faeroes, a very prominent high of 1028 mbar just northwest of the Azores, and a moderate northwesterly airflow over the UK. It was the 18th most northerly May in 141 years of records.
Mean maximum temperature during May ranged from 16.2°C at St James's Park (London) to 9.3°C at Fair Isle (between Orkney and Shetland), while mean minimum temperature varied between 8.9°C at St Mary's (Isles of Scilly) and 3.4°C at Loch Glascarnoch (Wester Ross). Both daytime and night-time temperatures were between 0.5 and 1.5 °C below the 1981-2010 normal in nearly all regions. The Central England Temperature (CET) of 10.3°C was 1.4 °C below the long-term mean - the lowest in May since 1996. In the last 100 years there were 12 colder Mays, four with the same mean temperature, while 84 were warmer.
The highest maximum at a standard site (i.e excluding rooftop and mountain sites) in the UK was 23.7°C recorded at Crosby (Merseyside) on the 7th and also at St James's Park (London) on the 31st, while the lowest minimum was minus 4.8°C at Tulloch Bridge (Lochaber) early on the 2nd. The lowest daytime maximum was 4.1°C at Braemar (Aberdeenshire) on the 23rd, while the warmest night was that of the 20th/21st with a minimum of 14.4°C at Thorney Island (West Sussex).
Rainfall averaged over England and Wales during May was 74mm which is 114 per cent of the average for the standard reference period 1981-2010. Averaged nationally it was somewhat wetter than the last four Mays, but marginally drier than that of 2008; in the last 100 years 27 Mays were wetter while 73 were wetter. The equivalent figures for Scotland were 74mm and 123 per cent of the normal amount, and for Northern Ireland 78mm and 139 per cent. Monthly totals at routinely-available sites varied between 265mm at Achnagart (Wester Ross) and 31mm at Shoeburyness (Essex). The heaviest daily fall was 72mm on the 14th at Pembrey Sands (Carmarthenshire).
Sunshine averaged over England and Wales during May was 202 hours which is 100 per cent of the 1981-2010 mean, rather less sunny than each of the last five Mays, but sunnier than May 2007. In the last 100 years, 52 Mays were sunnier while 48 were duller. The equivalent figures for Scotland were 176 hours and 99 per cent, and for Northern Ireland 184 hours and 90 per cent. Largest total in the UK was 247 hours at Guernsey (Channel Is) and the smallest was 119 hours at Eskdalemuir (Dumfriesshire).
Strongest winds during May occurred between the 9th and 14th with gusts to 62 knots at Mumbles (near Swansea) on the 9th.
By Philip Eden