When will a cold month signify global warming?

Spring has been rapidly catching up during the recent mild spell, but although February temperatures were below average it was only the coldest for 3 years! Interestingly, the temperatures have been below average in all bar 2 of the last 12 months. A worrying trend towards global cooling? ....er, no. Firstly let's look at these statistics. They relate to a garden in south London and cover the values since 1988, a mere 20 years. Official climatological statistics cover a period of 30 years. The current period that is frequently alluded to by the media covers the years 1971 to 2000. It could be argued that the temperatures derived from these data sets are anomalously high, containing, as they do, more than their fair share of both mild winters and warm summers. However, when figures for the years 1941 to 1971 are compared to those from 1971 to 2000 they show considerable warming, a point not lost to advocates of global warming. In 2 years time the latest set of averages will appear, and they will probably show further warming. The tyres on the global warming bandwagon may then begin to deflate as monthly comparisons with the new figures are increasingly likely to show 'cooler' months unless there is a consistent temperature rise. It could become a very frustrating time for politicians trying to persuade a sceptical public that a 'cold' month would have been defined as a 'warm' month 30 years ago!! By the way, the period February 1900 to December 1902, a total of 35 months, only produced 6 months with above average temperatures.......but that was long before global warming.

The worst winter in living memory (depending on age!)

It has probably been the worst winter for reporting weather facts since records began, but what about some real statistics. Okay, that's boring, but with the media telling us that the 'Big Freeze' is over it may be time to put some sobering thoughts together. Comments at the local bus stop range from 'Don't remember a winter like it' to 'Winters were often like this when I was young'. Well, yes, both statements could be true, depending on age. The Met. Office defines 'winter' as the three months December, January and February. In this winter, none of the months have been record-breaking in this area. December was the coldest since 2001, January was the coldest since 1997, and this month, although the coldest since 1986 at the moment, will probably end up as the coldest since 1991 or perhaps 1996. So, certainly no extremes there. The 'winter' started early for the media with October snow around London, and further snow fell in November, although that month, as a whole, was milder than average. Of interest, is the fact that the three winter months (unless the rest of February becomes very mild indeed!) have all been colder than average and the mean temperature is comparably cold with only 3 winters during the last 30 years. There is no way (famous last words!!) that this winter will be as cold as that of 1978/79, but it will probably be the coldest since 1995/96, perhaps the coldest since 1990/91, and maybe the coldest since 1985/86. If colder weather returns at the end of the month, then it will be the coldest winter in this area for 30 years, and for many, many people that's outside of 'living memory'.

A Rare 'Since Records Began'.

After 20 years of noting the daily weather, it becomes increasingly rare for new records to appear. Yesterday was one of those record-breaking days. The rainfall total, 22.0mm, beat the existing February record, set on the 24th in 2000, when 21.1mm fell. High daily rainfall during February is quite unusual, and in this area a total of 20mm appears to have been exceeded on only 3 more occasions. Namely, in the years

1925, 1933 and 1951. The wettest day was the 13th February 1925 when between 25 and 30mm of rain fell locally. Of interest, but not statistically significant so early in the month, a wet February in this area, with rainfall over 70mm, has only been accompanied by a cold February, with a mean temperature below 4.0 C, on one occasion since 1890, and that was in 1900! Another 18mm is needed to keep the rainfall part of the record at this site, and with a mean temperature of 1.3C, some mild days (and nights) are needed to spoil the other half of the potentially record-breaking equation.

The heaviest snow in South London since.....

The 19 centimetres of snow that fell yesterday and overnight has got us trawling through the record books. 'The snowiest since February 1991' is a typical quote from the media, but in that month, the Morden area only had 16 centimetres of level snow. Back in January 1987, it was bitterly cold and there were some deep drifts, but again the level snow was only 16 centimetres. Snow stayed on the ground for a while in the winter of '81/82 but not particularly deep, and then it's back to the 'winter of discontent' - 1978/79. Certainly on hills, and particularly in north London, snow depths exceeded 20 centimetres, but not in Morden. Early March produced depths close to 15 centimetres, but December 1962 had heavy snow on Boxing Day http://www.london-weather.eu/article.102.html, followed by further significant falls later in the month. The resulting depth was 25 to 30 centimetres. That's where the record lies.... so far!

'Snow Breaks the Drought'... but not any more

The light snow that fell overnight and early this morning marked the end of a 16-day period without measurable rain. In the old days, when City gents wore bowler hats and Christmas crackers only came from Woolworths, a spell of 15 days, or more, without 'significant' rain (less than 0.01 inches, or 0.25 millimetres) was known universally as a 'drought'. It was a term reluctantly used by meteorologists but regularly dug up by the media. Fortunately, since the real droughts, especially in Africa and Australia, have been vividly portrayed on our television screens, a lack of rainfall has been taken more seriously. However, to get back to the quirky old 'drought'. There have only been 3 occasions during the last 20 years in this part of London when a 15-day dry spell has encompassed the winter months (December, January and February) and not at all when the majority of dry days occurred during December! The 16 consecutive 'dry' days is nowhere near a record. In 1959, http://www.london-weather.eu/article.99.html central London had no measurable rain from the 24th January to 20th February, a total of 28 days.

Wettest day of the year in London?

Yesterday was the wettest day of the year with 25.4mm (exactly 1 inch) of rain falling in the 'Rain day' that stretches from 09 to 09 GMT. It was not a record breaker, nearly 32mm fell in December 2002 and almost 30mm fell in 1995. Boxing Day 1886 appears to have been the wettest December day, but as some of the totals included melted snow a cynic may question the validity of the readings. The numbers for that day included 46mm for Kensington and Brixton and 60mm for Hampstead. In recent years, 34mm fell in parts of southwest London during December 1979. Interestingly, the whole rainfall event this December covered 2 'Rain days' and the total came to nearly 36mm. It commenced around 0100 hours on the 13th and then rained continuously until 2300 hours, a total of 22 hours. That in itself is not a record. During June 1903 parts of north London had over 58 hours of continuous rain. By the way, a few days after that rain a three week 'drought' commenced!

Sunny Weather in London

After 3 dull days the sunshine that arrived today was to be welcomed. If it wasn't for a few minutes of low cloud at either end of the day the sunshine could have been unbroken. The 1st of December is potentially the sunniest day of the month with the daylight fractionally longer than on any other December day. This potential is seldom realised of course, but in 1954, a mild and sunny December occurred, and there were 7 hours of sunshine on the opening day. Two years later it was also mild during December but there were only 9 hours of sunshine all month. The Clean Air Act of 1956 helped to reduce pollution in London and smog is now almost unheard of. Fog is also a rarity now in Greater London, and the dreadfully dismal months of the 19th and early 20th centuries are behind us. There will probably never be a repeat of December 1890 when much of London had less than 30 minutes of sunshine all month, and parts of the West End remained completely sunless.