The mean temperature for December since 1900 in southern parts of London is around 5.2 degrees Celsius. In the last 20 years this figure has risen to 5.8 C. Whether this is part of a natural cycle or man-made climate change is a debate for another place. This mean temperature consists of an average maximum of 8.0 C (8.1) and an average minimum of 2.5 C (3.6) . The sources of information are from several semi-urban sites with similar soils and at similar heights above sea level. Inevitably there can be wide differences in temperatures over small distances, especially at night. The increasing urbanisation of south London during the early part of the 20th century, and the introduction of the Clean Air Act in the mid 1950s have also been factors in determining temperature levels.
In recent years, the talk has been more about mild Decembers than cold Decembers, and although there was over a week before Christmas last year (2009) with snow on the ground, the month as a whole was only ranked 29th coldest. The coldest so far this century was 2001, ranked 27th. December 1995 was a fairly wintry month, ranked 13th, but with snow only falling on 8 days and lying on just 5 days. One needs to go back a generation to find a real 'icy grip' December, but in the last 110 years there have been several of them.
Number 10= 1906 Mean Temperature 3.3 Celsius
November 1906 was quite mild and changeable and this unsettled theme continued into December. However, after some mild weather during the frst week it became colder. There were some sharp frosts, and towards the end of the month it became snowy. Around 5 to 10cm of snow fell on Christmas Day night and at first on Boxing Day, and this snow lasted for the remainder of the month. No exceptionally low temperatures occurred but the maximum stayed a degree below freezing on the 23rd, and a minimum of minus 5 C. was recorded early on the 26th. The rest of the winter was generally rather cold, dry and sunny.
Number 10= 1939 Mean Temperature 3.3 Celsius
The latter part of the autumn of 1939 was dull and wet. After a cold October, November ranked as the 8th mildest since 1900 with no air frosts until the 4th week of the month. December started mild and wet, and the maximum temperature on the 1st reached 13 C. However, the weather then became rather cold and mostly dry but often dull. Although there were several frosty nights, very cold conditions only set in during the last few days of the month. Early on the morning of the 30th the temperature was only minus 7 C, but for this winter worse was to come. January 1940 was snowy and bitterly cold. (ranked 2nd coldest since 1900). February was also fairly cold, but only ranked 20th coldest.
Number 9 1976 Mean Temperature 3.2 Celsius
The hot summer of '76 was legendary, but the chilly December that followed has been largely forgotten. November was changeable and fairly wet but with temperatures not far from average. December started in a similar vein but northerlies briefly produced lower temperatures and frosty nights around the middle of the first week. A wet and windy spell of weather at the end of the first week was followed by chilly northwest winds, and then mainly dry and cold anticyclonic conditions during the second week. Rain and sleet on the 17th was followed by several rather cold and damp days. However, after a mild start to Christmas week, it became colder again with some frosty nights but little in the way of snow. The end of the year was milder and although the following January was ranked 27th coldest (similar to January 2009) the remainder of the winter was mostly mild.
Number 8 1946 Mean Temperature 2.9 Celsius
November 1946 was frost-free and December began mild. However, the rest of the month produced a few mild and damp days, some cold and snowy days; but many crisp and,sunny days after sharp overnight frosts. A frosty spell after mid month resulted in a minimum temperature of minus 7 C early on the 21st, followed by a high of only minus 2 C during the day. The subsequent January was fairly dry and sunny, and although mild at times, particularly around mid month, the latter half became bitterly cold and snowy. The month was ranked 10th coldest, but February was far worse. There were frequent snowfalls, and in a month when maxima failed to rise above 5 C, it was generally bitterly cold and often windy. As a result, it was ranked as the coldest February since 1900.
Number 7 1916 Mean Temperature 2.8 Celsius
There were some cold days in a largely unsettled November with the changeable weather continuing into the early part of December. A cold spell around mid month gave some sharp frosts, and although it became milder for a while around Christmas, the temperature on the 27th failed to rise above minus 2 C. The end of the month was mild, and on New Year's Day the temperature rose to 12 C, but the following 4 months were cold and often snowy. January 1917 was ranked 11th coldest; February 1917 was ranked 10th coldest, but in, what proved to be, a very prolonged winter, March 1917 was ranked as 2nd coldest and April 1917 was the coldest of all the Aprils, thus ranked 1st.
Number 6= 1962 Mean Temperature 2.6 Celsius
March 1962 was the coldest on record and this began a long sequence of cold months only broken by a slightly milder than average October. The oft quoted cold winter of '62/'63 had some very cold, but foggy, weather during the first week. The fog was persistent and often freezing. The temperature on the 5th remained below freezing all day. Around mid month it became very mild, and although the early part of Christmas was cold, the snow held off until Boxing Day afternoon but then 20cm fell. Snow then covered the ground for the rest of the month. It was the start of a memorable winter with snow and ice covering most of the landscape until late February. January 1963 was ranked as the coldest since 1900 and February 1963 was ranked as the 4th coldest.
Number 6= 1927 Mean Temperature 2.6 Celsius
The autumn of 1927 was generally rather cold and often wet. After a mild start to the month, December became cold after mid month with occasional sleet or snow. On the 18th, the temperature only reached minus 2 C, but an incursion of mild air resulted in heavy rain on Christmas Day. This was followed by sleet, then wet snow, on Boxing Day. Further snow blanketed the ground on the 27th and a deep layer of snow remained for the rest of the month. January 1928 was a very unsettled month with strong winds, heavy rain and above average temperatures. There were sunny spells between rain bands, and in February sunshine became abundant. It was was often warm sunshine, and February 1928 was the 15th mildest since 1900.
Number 4 1917 Mean Temperature 2.4 Celsius
After a dry, but mild, end to the autumn, December began mild and sunny. The sunshine frequently returned during this dry month, but it was often cold with very few frost-free nights. There was some very cold weather in the week before Christmas, and on the 19th a maximum temperature of minus 2 C was recorded with minus 5 observed on the following night. However, snow amounts were small, and fears of a repeat of the previous cold winter proved groundless. January 1918 was changeable, but often sunny, and with temperatures close to average. Some snow occurred during the second week and the end of the month was fairly cold. However, after a cold day on the 1st, February was a mild and dry month.
Number 3 1950 Mean Temperature 2.0 Celsius
There was a chilly end to November in 1950. The maximum temperature on the 26th was only 2 C. December started mild with a high on the 1st of 11 C. However, the first fortnight of the month alternated between cold and rather mild weather. On the 13th the temperature fell to minus 4 C, but nights were often too breezy or cloudy for sharp frosts. The temperature barely rose above 1 C on the 15th, but in a month when sleet or snow fell on nearly every other day, the coldest weather generally occurred during the second half of December. Even though wintry precipitation was a frequent visitor, there was very little lying snow. The remainder of the winter was very changeable. It was rather mild in January 1951, and temperatures were close to average in February. Both months were wet, and although both sleet and snow were observed, they were transitory features with lying snow largely absent.
Number 2 1933 Mean Temperature 1.8 Celsius
Although this month is ranked 2nd coldest, it was neither snowy nor bitterly cold. The year had been notably dry and sunny, and the latter part of the autumn was dry. The mostly dry weather continued through December with rain (including a little snow) recorded on only 5 days. However, it was the persistence of the cold that was remarkable. The highest temperature recorded during the month was only 7 C., but on each day the temperature rose above freezing. However, the maximum on the 14th was only 0.1 C., and even though night-time temperatures failed to dip below minus 4 C, air frost was observed on 25 nights. The remainder of the winter was dry, particularly during February 1934. Temperatures were close to average during January, and although February was rather cold, frost,y nights rather than snow, continued to be the main weather feature.
Number 1 1981 Mean Temperature 1.6 Celsius
The coldest December since 1900 would only have ranked 8th and 7th if it had been either a January or a February respectively. Nevertheless, this month had some truly wintry weather. The preceding November was mild, and December began fairly mild as weak weather systems moved southeast around an area of high pressure anchored to the west of the British Isles. During the 7th, a series of depressions tracked southeast across central Britain with substantal amounts of snow over Scotland. On the following day rain turned to snow across London as very cold air encroached from the north, and the maximum temperature was 2 C. Several day of cold and rather cloudy weather followed, although sufficient cloud breaks occurred to give some sharp frosts. On the 11th, a depression moved east along the English Channel and heavy wet snow fell on its northern flank. In South London, 15cm was measured and the maximum temperature for the day was 1 C. Cold and frosty weather then returned, but on the 13th another depression moved east but this time it was further north. Snow turned to rain, and the temperature on the 14th rose to 8 C. The cold conditions featured again from the 15th with some cold nights in particular. On the 20th, rain, preceded by sleet and snow, spread from the west, but the mild air was repelled and snow returned from the east during the 21st. Further snow fell at times around Christmas and some severe frosts occurred. The last few days of the month were milder, though, and the maximum temperature on the 30th was 11 C. Further bitterly cold weather occurred during the first half of January otherwise the rest of the winter was mainly mild and changeable.
The coldest December of them all
There were several Decembers between the mid 17th century and the beginning of the 20th century that were colder than 1981. The Decembers of 1676, 1788, 1796 and 1878 were notable, but it was the December of 1890 that stood out. Firstly, there was less than 1 hour of sunshine all month, and secondly the severe weather was preceded by intense cold at the end of November. On the 23rd of November the temperature exceeded 14 C., but on the 28th the maximum was only minus 4 C. with overnight minima around minus 6 C. At the beginning of December it was fairly mild for a while,
and the temperature on the 4th almost reached 7 C. However, the second week turned cold and bitter easterlies arrived with snow, and although quantities were not great, snow was observed on 12 days. From the 10th to the 19th temperatures remained below freezing day and night. and included a maximum of minus 6 C on the 14th. The minimum on the night of the 21st/22nd was minus 12 C and the very cold weather persisted until the middle of January 1891. It became sunny, though, and February, although rather cold, was extremely dry.
.........and now December 2010
It was the coldest since 1890 with a mean temperature in South London of 1.2 C!