The Fog Myth

The fog which descended over parts of London and persisted through much of Sunday helped to fuel the myth that London is a foggy city. Certainly the pea-soupers that plagued the Capital in the past justifiably gave the city a bad reputation. The polluted fog of early December 1952 was probably responsible for over 4000 deaths in Greater London and this eventually led to the Clean Air Act of 1956 and a decline in the instances of choking fogs. Nowadays, the heat island of London helps to reduce the number of 'natural' fogs and the few fogs that do occur are usually confined to, or are at their worse in, low-lying suburban areas of London. The statistics for Morden show that since 1988 November, on average, has been the foggiest month. However, a day with fog (defined as a day when visibility is below 1000 metres at 0900 UTC) has only occurred on 19 occasions, and the highest number of foggy days in any month has only been 4. Thus the 'foggy London' tag has well and truly been laid to rest.

The end of the dry spell

After 17 days without measurable rain, the 0.2 millimetres that fell yesterday evening was enough to break the dry spell. Most years have a prolonged dry spell (15 days or longer) with Spring and Autumn months most likely to see one. September and the beginning of October have had 3 dry spells in recent years. 1997, 2002 and 2007 each had between 15 and 17 consecutive dry days, and back in 1969 only 3 millimetres of rain fell throughout September. The most prolonged autumn dry spell in the London area occurred from the 14th September to 9th October 1921 (26 days). However, there were several lengthy dry periods that began in August, notably 23rd August to 28th September 1929, and 15th August to 20th September 1959, both 37 days. In the extended good summer of 1959 there was a further 17 days of dry weather from the 23rd September until 9th October.

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'.

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.