Upper and collocated surface lows across eastern England will slowly drift east across the N Sea during the evening. An unstable Wly veerying NWly to Nly flow will cover England and Wales.
… ENGLAND and WALES …
Cold mid-level temperatures of upper low atop moist diurnally heated surface airmass will create steep lapse rates which will support the re-development of scattered heavy showers and thunderstorms today. A zone of wind convergence shifting southeast across England and Wales during the day could be the focus for storms to organise and train along, bringing a threat of localised flooding where they do organise. Otherwise weak vertical shear will mean showers and storms that develop will be dis-organised and pulse-type and will limit the potential for severe weather. Any showers/storms may produce hail and, like yesterday, there could be a few funnels or even brief weak tornadoes / waterspouts – especially where surface convergence combines with buoyant and strong updrafts.
What do the risk levels mean?
Thunderstorms - Severe thunderstorms unlikely to occur, slight risk of hail, gusting winds and localised flooding.
Slight Risk - A slight risk of severe convective weather exists. Hail >2.0cm diameter, wind gusts exceeding 50mph or 5-10% risk of a tornado within 50 miles of a point, or > 30% risk of localised flooding.
Moderate Risk - A moderate risk of severe convective weather exists. Hail 4-5cm in diameter, or wind gusts of 60-70mph, or a 10-15% chance of a tornado within 50 miles of a point, or >50% risk of localised flooding.
High Risk - A high risk of severe convective weather exists. Rarely, if ever used on the UK. Hail >5cm, or wind gusts in excess of 80mph, or >20% risk of a tornado within 50 miles of a point, or >70% risk of localised flooding.