Last of the Summer Days?

Time to get the potatoes in before Autumn truly arrives. Although temperatures above 20 Celsius in October are not unusual, after the disappointingly cool September in London, this short warm spell is much welcomed. The maximum temperature of 22.2 Celsius today is over 1 degree warmer than any maxima recorded during September, and is the highest this late in October since 2001. There were only 4 days during August that were warmer, 13 days in July and 7 in June. In October 1921, the first 11 days of the month had maximum temperatures above 21 Celsius, and on the 5th and 6th of October in that year the high was close on 29 Celsius at several places in London, including Kensington Palace, Greenwich, Camden Square and St James's Park.

Although rain threatens for the next couple of days, it's now 11 days since any measurable rain fell in Morden. With little, if any, rain likely during the last week, it looks as if September is going to be another dry month. That will make 3 out of the last 4 months with below average rainfall; and 6 out of the last 7 months have had temperatures below the 20 year average. The scientific community regularly assure us that the very wet weather (but not everywhere!) is part of global warming, and the El Nino is responsible for the lower temperatures. Of course, the threat of Global Warming cannot be ignored, but perhaps the trend towards sixties fashions has been followed by a return to sixties weather. Let's hope not. Apart from the severe winter of '62/63 most of the weather was instantly forgettable. Some of the fashions and much of the music appear to have lasted in the memory somewhat longer.

The Screen has a make over.

Every now and again the screen housing the thermometers needs renovating. With no spare available, a little improvisation is called for to maintain reliable temperature readings. The 'Official' box, temporarily absent for repair, spent many years housing thermometers on State House, a high-rise office block in High Holborn, London. The block succumbed to concrete rot and has since been replaced, and the 'London Weather Centre' that used to take readings from it's base opposite in Penderel House has long since moved on. The Stevenson Screen, the official name for the louvred 'bee-hive' box was invented by Thomas Stevenson in 1864. He was a civil engineer responsible for the design of many lighthouses but the screen is maybe his enduring legacy. The World Meteorological Organisation recognize the Stevenson Screen as the standard housing for meteorological instruments. It has to be in an open area between 1.25 and 2 metres above the ground. Originally this screen was around 80 metres above street level. It has led a Jeckyll and Hyde existence, perhaps appropriate considering the inventor was the father of Robert Louis Stevenson, the author of The Strange Case of Dr Jekyll and Mr Hyde

To put it simply, there are 3 main types of thunderstorm in this country. The most common of these is the all-year-round storm which starts with a build up of cloud during the morning, a couple of rumbles from a cumulonimbus cloud in the afternoon, followed by a fine evening. In the winter months this type of storm is usually found on windward coasts. The second type is formed by the destabilisation of the air well above the surface, usually 6,000 feet AMSL or higher. This commonly occurs when cool Atlantic air is about to bring an end to a hot spell. In recent years this form of storm has been fairly uncommon, although one occurred here on the 28th July. The first sign of these type of storms is usually several afternoon reports of thunder from Brittany, followed by a quick migration northeastwards, reaching Southampton in the early evening and London bewtween 9 and 10 pm. For the good folk of Kent last night's storms were closest to the second category. Although very little surface wind blew in association with the storms, it was certainly not true that they were slow moving. In fact the storm clouds were moving at around 35 knots. Rather than one storm lasting a long time, it was a series of storms generating within a band that ran from the East Sussex coast towards Essex. Now, the third type of storm is the 'swing-seat' one. This occurs on a warm summer's evening when several storms develop or move into the area, produce a vivid display of lightning, numerous rumbles of thunder, but are never overhead. Thus, it remains dry and warm, and a free display of nature's power can be observed accompanied by a glass of claret and a packet of peanuts. That was the thunderstorm that occurred over this part of South London yesterday evening.

Where is the Summer Heat?

Yesterday (Thursday) was the warmest day of the 'Summer' so far. Here in Morden, the temperature reached 27.6 Celsius, central London and and Northolt reached 27.5 Celsius, and Heathrow Airport managed 28.2 Celsius. Today is less warm, but humid, and over the next few days it looks like being warm but probably not hot. In the London area there is usually at least one day in the Summer when 28 Celsius is comfortably exceeded, and, of course, there is still plenty of time for high temperatures. In recent years, some record-breaking maxima have occurred during August. However, if the 27.6 Celsius should prove to be the highest maximum, it would then be the lowest yearly maximum since 1978!

Not Another Wet July!

The first rain of the month has just fallen but there's a long, long way to go before we reach last July's total of 124mm. It was the second wettest July for at least 100 years in South London, with only July 1956 wetter. Perhaps surprisingly, none of the top 10 wettest Julys correlate with the top 10 coolest Julys. During the wet Julys, rain is often of a thundery nature, and although the weather may be cyclonic, there are often spells of warm sunshine between the downpours. However, out of the 9 Julys when 100mm was exceeded, only the Julys of 1925 and 1941 could be described as rather warm. In association with all the wet Julys, the following Augusts were cool, and sometimes very cool. Let's hope it's not another wet July this year.

Cool Junes

The last time that temperatures were below normal during June across south London was in 1991, so statistically we are well overdue for a cool June. To add to the statistical woes, 3 out of the last 5 Junes have been 'top ten' Junes. In other words, amongst the 10 warmest Junes since 1900.

During the '70s and '80s poor Junes were in the majority. In fact, only 2 Junes in each decade could be described as warm; those of 1970, 1976, 1982 and 1989. This early summer month was particularly poor in 1971 and 1977, but in 1972 the coldest June of the century occurred with the the temperature failed to rise above 20 Celsius all month. The 3 disappointing Junes in the '70s were all dull, and 1971 produced the second wettest June of the century. Rainfall was above average in June 1977, but perhaps surprisingly, June 1972 was a very dry month in South London. Looking at the synoptic charts for the month, it certainly appeared very unsettled, but Atlantic rain bands only yielded small amounts of rain, and the 'showery' air behind the fronts only produced limited amounts of convection. However, after a sunny start to these days, cloud developed during the mornings and spread across the sky to produce gloomy, but mainly dry, afternoons, the worst type of summer weather.