Sunday, 4 October 2009

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.

Saturday, 22 August 2009

Not a vintage August.....but

In recent weeks there have been less grumblings about the poor summer. In fact, in the London area August has been a month of consistently warm weather. The temperature has reached, or exceeded, 20 Celsius on every afternoon since 20th July, a total of 30 days! If maxima reach 20 Celsius on each of the next 9 days, then this August will be record-breaking. Even in the hot Augusts of 1995 and 2003 there were days when the temperature failed to reach 20 Celsius, and further back the August of 1976 had some cool days during the last week. It remains to be seen if this month produces a record, but in this so-called poor summer there have been 72 days (including April and May) with highs of 20 or more. In the memorable summer of 2003 there were 117 warm days, including 22 maxima above 20 Celsius during September.

Tuesday, 4 August 2009

A barbecue summer

As the baying pack from the media continue to taunt the rather disingenuous attempt by the Met. Office to tell us it almost is a 'barbecue summer', let's find a few facts least for this part of the country where 15 million potential barbecuers live.
There is a reason why barbecues are more common in Mediterranean countries and the USA than here. They have warm and dry summers, and we don't. Up until the mid 70s plastic macs donned for a trip to the pub were more common than plastic plates and cups on the patio, but then the summer of '76 arrived. The general public realized that the sky didn't leak every day, and suddenly al fresco hit London. The barbecue grills rusted for a while in the late 70s and 80s, but from the end of the decade onwards a barbecue grill became a 'must have' along with the 4-wheel drive and a mobile phone. In many years the weather co-operated, but in this summer, like in its two predecessors, plastic mac days returned.
The official statistics put an emphasis on the mean temperature and the total rainfall, but if the nights are cloudy and windy they're often milder than after warm and sunny days. Perhaps more relevant are 'days' with rain falling and daily maximum temperatures, and these paint a poorer picture of the summer weather so far this year.

May, perhaps perceived as a tad early for a trip outside, did produce a few reasonable days during the last week, and June was a pleasant month in London. However, using maximum temperatures, it ranked cooler than the recent Junes of '76 , '89, '92, '96, '03, '04 and '06. Although rainfall totals were below average, the number of days when rain was recorded was above normal
For many people in Southeast England July was a poor month. After the 2nd, winds were from the southwest on nearly every day. The breezes were brisk at times and on the south coast they were often fresh or strong. The temperature has failed to rise above 21 Celsius since 3rd July on the Sussex coast, and although it has been somewhat warmer at times inland, in south London there have only been 4 cooler Julys (based on maximum temperatures) in the last 20 years! The other interesting statistic is with regard to rainfall. Okay, it was a wet month around London, but not exceptionally so. However, measurable rain fell on 20 days.....4 more than the previous July record during 20 years of observations, and what's more 6 of the remaining 11 days had some rain, but not enough to measure.
The Met. Office have 'revised' their forecast for the rest of the summer, but while they keep digging their hole, it remains to be seen if nature has the last laugh and produces a warm and dry August.

Friday, 19 June 2009

The Summer when the grass turned brown.

For many parts of southern England June looks like being the 4th consecutive month with below average rainfall, but at the moment the fields and gardens are as green as in the Emerald Isle. Not so in June 1976. March and April were both very dry in that year, with monthly rainfall totals in southwest London below 10 millimetres. May was slightly wetter, but still with a total rainfall more than 50% below average. It was a sunny Spring, but May was actually cooler than this May (2009). June 1976 began fairly cool and changeable. The temperature on the 1st only reached 19 Celsius and nearly 2 millimetres of rain fell overnight. The following 2 days were even cooler with highs of only 16 Celsius, but then pressure rose and so did the temperatures. The maximum on the 9th reached 30 Celsius, and although temperatures then fell closer to average, it remained largely dry with sunny spells. During the third week it was rather cool and changeable, and on the 20th nearly 7 millimetres of rain fell, but the last 10 days of the month were dry, hot and sunny. On the 22nd the temperature reached 27 Celsius, but then daily maxima read:- 30,31,33,33,34,33,29 and 29. It came as no surprise that the grass turned brown. It was not even a surprise that pubs around London ran out of beer. The Summer of '76, a record-breaker.

Sunday, 7 June 2009

It Never Rains but it Pours

The proverbial phrase in the title must be going through the minds of many members of the Labour Party, and is probably reinforced by the real thing falling from above.
As further storm clouds build, it's interesting to reflect on how bad June can be, meteorologically speaking of course.
The June of 1972 is often quoted as a bad one, but although it was very cool, the coolest in London since before 1900, it was also dry and not unduly dull.
The majority of very cool Junes have been wet, but given the thundery nature of rain in some summer months, wet Junes are not neccessarily cool. In June 1971 it was cool, very wet and also fairly dull, but for overall unpleasantness 1916 is probably the June winner. Apart from occurring in the middle of the 'Great War' this month was notable for persistently low temperatures and a huge sunshine deficit.
Last June (2008) was not too exciting, but since the cool 1991 June, the month has generally been noted for high temperatures (4 in the all-time top 10) and with only 1998 in the top 10 for high rainfall (90mm and placed at number 10!). It remains to be seen what the rest of this month brings, but even if it is as poor as 1991, there is hope. The storm clouds cleared in that year and gave a very uplifting July, August and September.

Tuesday, 12 May 2009

That magic 70 mark

April was the 3rd warmest in this area since before 1900, BUT, the temperature failed to reach 70 Fahrenheit (21.1 Celsius), the much quoted value favoured by the tabloid media. So far, the maxima have not exceeded 21 Celsius this month either, and that is more unusual. In 20 years of records in Morden, the temperature had always reached 21 Celsius by this time of year. As the blustery northeast wind continues to bend the trees under cloudy skies, there seems little prospect of higher temperatures in the immediate future. A scan through the records reveals 1975 as the last year when the temperature stayed below 21.1 Celsius until the end of May but, after a cold start to June, that Summer became very good. Prior to that, the year 1972 had no maxima above 21 Celsius by the end of May, but the June of that year also had no highs above 21 Celsius! The June of 1972 was the coldest of the century, and the rest of the Summer, although dry, was unpleasantly cool.

Tuesday, 24 March 2009

Yes, it's Spring

Yesterday, the first significant rain since the 10th March occurred. It marked the end of a very sunny, and mild, spell of weather that has helped to push Spring briskly forward after the relatively cold Winter. In Morden, March is, on average, the driest month of the year. There have been 10 Marchs in the last 100 years when less than 10mm of rain were recorded in the area, the most recent being in 1990 when 5mm fell. The driest March was in 1929 when just 1mm of rain was measured. By way of a contrast, the cold and snowy February of 1947 was followed by a very wet March with 118mm of rain falling in southwest London. It remains to be seen at what end of the rainfall statistics spectrum the final figure for this March will lie.

Monday, 2 March 2009

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?, 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.

Saturday, 14 February 2009

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'.

Tuesday, 10 February 2009

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.

Monday, 2 February 2009

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, 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!

Monday, 5 January 2009

'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, central London had no measurable rain from the 24th January to 20th February, a total of 28 days.