Thursday, 21 October 2010

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.