A Lively Day!
On Tuesday 13th May, much of England and parts of Wales experienced a thunderstorm outbreak on a scale not seen so far this year. Showers in the south of England during the morning quickly developed widely by midday, thus by early afternoon very few locations across England were not seeing large cumulonimbus clouds on the horizon. But it was by late afternoon and towards evening that the real activity fired up!

A rash of torrential downpours aligned themselves and joined forces, with one such band spreading eastwards across East Anglia, and another becoming slow moving over the M4 corridor between Bristol and London. Thunderstorms also broke out across south-east England, and an isolated yet vigorous cell struck Cardiff. The latter produced hail in the region of 15-20mm in diameter, large enough according to one eye-witness report to set off whole streets of car alarms! At the same time, hail was observed stripping vegetation from trees near to Ipswich and localised flooding was affecting towns throughout the Midlands. Several small waterspouts were spotted off the coast of the Isle of Wight, and numerous sightings of funnel clouds were reported from other regions.

Perhaps the most striking region of storms developed from about 3pm from the south Midlands, stretching into south-east England. A dozen or so cells merged as a trough-like feature, moving slowly southwards and pivoting about the Bracknell region for 2-3 hours. Rainfall amounts exceeded 50mm/hr at times, and at one point the entire stretch of the M4 motorway disappeared beneath shoulder to shoulder thunderstorms. Many reports of cloud-to-ground (CG) lightning were amid the chaos, and traffic on the roads around Reading came to a standstill. Large hail was also reported from this band of storms, the image to the left showing 10mm diameter hail in Bracknell (courtesy of L. Gilchrist). Some locations saw hail accumulate to depths of almost an inch, resembling a winter scene in the storms' wake. Wednesday is set to be more settled in general, although storms may develop in eastern parts later.