The month was one of the warmest, wettest and stormiest Decembers since 1950.
With S/SW winds dominating, there was very little cold weather and, along with 2011, it was the sixth warmest December since 1950. The days were particularly mild with only three in the first week having a max below average. The max of 55F (12.6C) on Monday the 16th was the highest for that date since 1956. At night, there were only three slight air frosts, the lowest number in December since 1974. The mean max (5F above average) has only been higher in 1974 and 1953. With high pressure over the Continent the first 12 days were dry.
Then a very strong jet stream led a series of unusually deep depressions across the Atlantic to the NW of the UK. Their active fronts crossed the UK giving copious rainfall accompanied by frequent strong winds.
With the pressure in a Low in the Atlantic down to 27.5 inches (935mb) on the 24th, the wettest and stormiest period was from the 21st to 24th. There was an inch of rain (25mm) on the 21st and nearly two inches (45mm) on the 23rd/24th. Starting in the evening of the 23rd and through the early hours of Christmas Eve, the heavy rain was accompanied by a major gale. For eight hours or so there were frequent gusts of over 60mph and the Middy reported many trees down, homes suffering from prolonged power cuts and local flooding in Mid-Sussex.
The situation was broadly comparable to Christmas Eve in 1999. The Middy then reported, “Emergency services had one of their busiest nights ever as storms lashed Mid-Sussex on Christmas Eve.” Then, the emphasis was on the flooding, this time on the effect of the strong winds with the power cuts.
Winds were also strong enough to cause problems on the evening of the 18th and mornings of the 27th and 30th.
From Friday the 13th to Tuesday the 31st, rain or showers fell every day. Eight days had over half an inch of rain and the month’s total of 8 inches (204mm) made it the second wetttest December since 1950 after 1959 and the seventh wetttest of any month since 1950. As a prolonged wet spell it has now only been matched in October 1987, around the time of the Great Storm, and in October 2000, at the time of the exceptional autumn floods.
Although there were 12 sunless days, sunshine was 16% above average, as there were sunny days, such as Boxing Day, between the rain bands.
The Year 2013 was an eventful one. The year was memorable for the cold early months, the seventh best summer since 1950 and the wet, stormy weather of the final three months.
The cold first half of the year meant that the annual mean temperature was a little below average. With 1635 hours of sunshine, it was the dullest year since 2000, while 37 inches of rain (940mm) made it the second wet year in succession with rainfall 7% above average.