The first three decades of the century showed a gradual warming trend. Things were about to change. 1940 will be best remembered for the phenomenal January, with low overall temperatures, and an amazing ice storm. The winter 1939-40 was a hard one, and the first of three severe War Winters. There was snow cover for more than 50 days in northern Britain. It was the third equal (with 1916-17) coldest winter of the century (after 46-47 and 62-63), with a CET of 1.5C. It was an interesting summer, too, with a very warm June, a wet July, and dry August. July was the start of the longest string of consecutive colder-than-average months this century (although beaten by November 1878 to January 1880): 11 in all, up to May 1941.
January. The coldest month of any kind since 1895 (-1.4C CET), and eventually the second coldest January of the century (after 1963). The month started with a northerly airstream, but early in the month the winds turned to the east, bringing very cold continental air. It was clear and sunny, with hard frosts at night and several frost days. There was a severe blizzard on the 16th. On the 17th, the Thames was frozen over for the first time since 1880. The morning of the 21st gave the lowest temperature of the month: -23.3C was recorded at Rhayader (Wales), the record lowest Welsh minimum, with many places continuously well beneath freezing (e.g. only -4C maximum at Boscombe Down, Wilts.). There were heavy snowfalls in Scotland, with many places cut off. By the third week the Atlantic westerlies tried to return, bringing some heavy snowfalls. Most remarkably, there was a great snow and Ice Storm during the 27-30th, peaking on the 28th, but continuing in parts into February. Mild air approaching behind warm fronts from the SW met the cold easterly all the way from Russia. There was heavy snow over the north; four feet of snow in Sheffield on the 26th, and 10' drifts reported in Bolton on the 29th. Further south the lower air was warming up and was too warm for snow, but the rain froze as it fell, coating everything with a thick layer of glaze. The effects of the freezing rain was one of the most extreme weather events of the century. The south was particularly badly affected. Everything was coated in a thick layer of ice: phone wires 1.5 mm thick were coated with a 300mm diameter sheath of ice - up to 15 times their weight. Many large tree trunks and power lines were brought down. The area affected by the glaze reached from Kent to Exmoor and the Cotswolds, and from Sussex to Cambridgeshire and the north Midlands. It was a week before all the ice thawed; some places had snow on top of the glaze, with both remaining until the 4th February. Heavy snow and a violent gale swept the southwest.
February. Very cold for the first three days. The melting of the effects of January's great Ice Storm on the 3rd led to widespread flooding on the 4th. Foggy between the 5th and 9th. Very cold between the 10th and 19th. Colder than average overall, and a dull month everywhere.
March. Dry and cold at first but unsettled later. Milder than average.
April. Dull. Dry in the east and north, but wet in Wales and the west and southwest.
May. Warm (12.5) and sunny.
June. The warmest June of the century in Scotland, and at 16.4 ºC CET the second warmest of the century over England and Wales. The month started warm, following on from a fine May. It was hottest in the first ten days of the month, peaking at 33C at Cranwell (Lincs.) on the 9th. Very sunny and dry, but less settled in the second half. Indeed, Boscombe Down (Wilts.) only made 13C on the 23rd. Mountstewart, Co. Down in Northern Ireland, had 298 hours of sunshine, the record highest monthly sunshine total for Northern Ireland. Perth recorded 31.7 ºC (89 ºF) on the 6th, the highest temperature in Scotland since 12th July 1911 when 90F was recorded at Perth.
July. Cool and very wet: the wettest of the century for Scotland. The 10th was a very wet day, with 25mm of rain widely, and over 50mm in places as far apart as Aberden and Berkshire; Scarborough recorded 106mm. Large hailstones at East Kirkby (Lincs.) smashed glass and flattened crops. On the 11th, 80mm more on the Brecon Beacons, and 90mm at Redcar on the 17th. Flooding in Cromarty on the 26th. The end of the month wasn't quite as wet as the rest as high pressure settled over the south of the country. The start of 11 consecutive colder-than-average months - the longest such run of the century.
August. Very dry - the second driest of the century for England and Wales so far, with 18% of the long-term normal. Calshott (Hants.) saw just 0.4 mm of rain all month. No thunder recorded all month. An anticyclone formed over southern England at the end of July and stayed put through most of August. Much of southern England recorded no rain all month. Although it was often sunny (particularly early and late in the day), as the wind direction was often N or NW, it wasn't particularly hot. Windier and cloudier 19-24th. There was a chilly night at the end with a grass minimum of -2.7C at Greenwich on the 27th (though note the air minimum was still several degrees above freezing, at +6.5C).
September. August's anticyclone and dry weather persisted for the first week, but it got warmer: 30.6C in London on the 4th. Then it was more unsettled, although some parts of the SE still didn't have any rain until the 19th.
October. Dull and unsettled.
November. Second wettest month this century, with an England and Wales average of 197 mm, and fourth wettest in the long-running weather rainfall records. It must have made the Blitz even more miserable.
December. Dry and mainly anticyclonic, and sunnier than average everywhere. There were strong winds on the 6th.