Dry, but getting wetter!

The 23rd of May, the sun is shining, but rain over the weekend has reduced the Spring deficit and it remains uncertain whether the 'record dry Spring will become a reality. A mere 15mm will now take the 3 month total past that achieved in Spring 1976 but there are only 9 rain days left! Let's have a look at the latest charts. At the moment the radar shows a band of rain over Wales and that's forecast to weaken considerably as it moves southeast. Probably 1mm at most before it clears. Tomorrow (24th). Only an outside chance of a shower. 25th suggests a weak front late in the day or overnight, again less than 1mm. So, 6 days to go and 13mm. 26th will probably be showery, typically 2-5mm, with a ridge of high pressure helping to produce a dry day on the 27th. The 28th could well be a wet day 5-10mm, possibly more! Back to showers and around 2mm on the 29th followed by more substantial rain on the 30th (5-10mm) and then showers again on the 31st (about 2mm). Best estimate would suggest the record will be missed by close on 3mm. Bad news for the thrill-seeking statisticians. Great news for the gardeners!

Now it's seriously dry.

A few spots of rain fell this morning but now it's beginning to look very dry. The trees are losing their Spring lustre and the grass is turning increasingly brown. It's not surprising really. The total rainfall for this area since 1st March (66 days) is only 21.6 mm. To put that figure into context, the 20-year average fall for those 66 days in this area is 105mm, so the total this year is only just over 20% of the average. What of the rest of Spring? Will it beat the record? Interestingly, the average rainfall for the first 15 days of May is 15mm, but for the last 16 days of May the average is 29mm. Therefore, if 'average' rainfall occurs for the last 16 days of the month the record will not be broken! The total for the Spring would then be around 51mm which would rank this Spring as the 6th driest since 1900. However, if only 18mm of rain falls the record will be broken. In 4 of the last 20 years, and 21 of the last 110 years, there have been daily falls of over 20mm in this area during May. So, it only takes one big thunderstorm and that 'Dry Spring' record set in 1976 remains intact.....and by the way, the grass really did turn brown by the end of that Summer, all of it!

Not enough rain.....yet.

The heaths around London were tinder dry after weeks without significant rain, but west of London there were 9 or 10mm of rain during Saturday with parts of west Surrey having several millimetres more than that. Unfortunately most of east Surrey and south London had considerably less rain with typical totals 2 or 3 mm. In this part of south London the total rainfall since 1st March is only 21mm, still 19mm short of the 40mm that is needed to prevent Spring 2011 being the driest since before 1900. So, just 24 days left before 'Summer' arrives and will the record be broken. Obviously too early to say yet, and in showery weather totals can increase quickly. However, over the next few days it looks as if showers will be few and far between in this area, and although the further outlook remains generally unsettled, whilst the main area of cyclonic activity stays to the north of Britain, the prospect for substantial rain in south London stays small.

April 2011....a remarkable month

April 2011 was a sunny month, about the 15th sunniest since 1900. It was also a dry month, the 2nd driest since 1900 behind the April of 1938. It was also the driest early Spring (March/April combined) since 1938. However, the most remarkable feature about April 2011 was the temperature. It was the warmest April since reliable instrument records began in the 19th century, and in doing so beat the outstandingly warm April of 2007. To put the event into perspective statistically; the mean temperature for April 2007 was 13.0, which was a massive 1.4 Celsius higher than the previous record set in 1943. The mean temperature for April 2011 was 13.6! If the month was May instead of April it would have been ranked the 21st warmest May since 1900. The very dry ground aided overnight cooling, and although no air frosts occurred, the mean minimum temperature was only 2.5 Celsius above normal. The mean maximum temperature (19.3) was 4.9 Celsius above normal. This figure was truly incredible. Since 1900, there have only been 8 Mays with higher average maxima. None of these warmer Mays occurred between 1923 and 1988 inclusive. Not only were April 2011 days warmer than most May days, there were several summer months in recent years that have been cooler by day: namely the Junes of 1953,1954,1955,1956,1971,1972,1977,1978,1979,1980,1981,1985,1987,1988 and 1991: the Julys of 1954 and 1980; and the Augusts of 1956 and 1963. What next?

A mild February. Nature redresses the balance.

Although cold air continues to lurk uncomfortably close on the near continent, forecast charts for the remainder of the month generally suggest that mild weather will prevail. In fact the projected mean temperature in this area of 7.8 Celsius would rank February 2011 as the 4th mildest in the last 110 years, behind 2002, 1990 and 1961. In February 2002 there were no exceptionally mild days, but only 2 air frosts occurred in this snow-free month. In February 1990 there was sleet early on the afternoon of the 3rd, but only 1 air frost occurred and on the 23rd the afternoon temperature soared to a record-breaking 19.0 Celsius. In February 1961 there were several very mild, sunny days and the month was totally free of air frost and snow. Although this February is not going to be a record breaker it has certainly helped to redress the balance after the cold December.

The media snow circus has begun

The cold weather has arrived and journalists are posted in every corner of the land for the big chill. In reality, it may be the start of something big but in this area no records (yet!). A few flurries of snow around London are not unusual in November. Two years ago there was 1cm of lying snow on the morning of the 23rd. The last time we had a November day colder than today was 17 years ago, on the 22nd to be precise, when the maximum temperature was only 1.2 C. November 1993 was very different to November this year with plenty of cold weather and several very frosty nights with minima below minus 4 C. By the way, December 1993 was mild with only 4 slight frosts, and the lowest temperature only minus 1.2 C!

For snow and cold weather lovers late November 1890 was interesting. After an unremarkable early part to the month, the temperature at Kew exceeded 14 C on the 23rd. However, 5 days later the maximum was only

minus 3.6 C. The following December was the coldest on record. Although it was a relatively dry month, it was very dull with less than 1 hour of bright sunshine all month. Despite the extensive cloud cover, there were only 4 frost-free nights, and after a maximum temperature of minus 6 on the 14th, the minimum on the following night was minus 12 C, a value we haven't seen in this area since 1981!

Early sharp frost,but no record

The air temperature here fell to minus 2.7 Celsius last night.This was the lowest temperature in October since 28th October 2003 when a similar value was recorded. No monthly record was broken but the lowest temperatures have usually been logged during the last week of the month, and only on the 19th October 1926 has there been such a cold night in this area so early in the autumn during the last 110 years. At that time this area was given over to farmland!

The lowest temperatures measured in south London occurred relatively recently in October 1997. After a very dry September, some heavy rain occurred between 6th and 14th October and this took the monthly total above average. However, after mid month, rainfall totalled less than 2mm with sunshine helping to dry out the ground. The drying process accelerated during the last week as high pressure became established, the air descended and from the 28th until the end of the month the low-level inversion dissipated and all cloud, apart from some cirrus on the 30th, disappeared.

Very low humidities, light winds and dry soils combined to produce the perfect recipe for frost. Nature didn't disappoint with record-breaking low night-time temperatures on both the 28th/29th and 29th/30th. Wallington and Twickenham both recorded minus 5.2 Celsius on the 28th/29th, and here in Morden, after a minimum of minus 4.7 Celsius on the 28th/29th, the following night had a low of minus 5.0 Celsius. Perhaps more remarkable were the grass minima. Values of minus 13.2 and minus 12.8 over the 2 nights remain the lowest 2 consecutive grass minimum temperatures of ANY month since records began here in 1988. By the way, the grass minimum temperature last night was only minus 4.9 Celsius.