Not all Junes in southern England have been as warm, dry and sunny as this month. Exactly 100 years ago there was a prolonged downpour and flood without precedent in London's meteorological history. In over 300 years of rainfall recording in the capital June 1903 ranks as the wettest individual month, yet there was no rain at all during the first week, nor during the last ten days. In other parts of the UK it was a very dry month with less than 25mm of rain in parts of the north Midlands, Lincolnshire, western and northern Scotland, and Northern Ireland.

The wetness of a wet June, at least in lowland Britain, usually derives from torrential short-lived dowpours, often localised and thundery, and frequently accompanied by great heat. In 1903, by contrast, June's wetness was a consequence of long-continued steady rain lasting for many hours at a time, unaccompanied by thunder, and associated with unseasonably low temperature. It was the sort of rain more appropriate to autumn than to midsummer.

At Kew Observatory 183mm of rain fell during the middle fortnight of the month - over three times the normal amount for June, and nearly 30mm more than the next wettest. Even more rain fell in north and central Surrey, including 197mm at Waddon New Road in Croydon, 204mm at Addington, 206mm at Brimstone Barn, near Croydon, and 226mm at Carshalton. It is estimated that the rainfall averaged over what now constitutes Greater London was approximately 161mm, which converts to 288 million tons or 64 billion gallons of water, and that is more than 10,000 gallons per person.

Throughout the period a complex depression lay over France, southern Britain and the Low Countries, while high pressure was centred between Scotland and Iceland. The resulting north-easterly airflow fed very moist but very cool air from the southern North Sea across southeast England, so daytime temperatures rose little above 10C on the wettest days. During the middle of the wet period, from lunchtime on the 13th until late evening on the 15th, it rained continuously in central London for a period of almost 59 hours. This is the longest period of unbroken rain ever recorded in a populated part of the United Kingdom.