DAY 1 CONVECTIVE / THUNDERSTORM FORECAST - MON 20 MAY 2019
Like Sunday, a broad upper trough will extend SE into Europe from the far N Atlantic on Monday with the UK under the trough axis. A slack flow will cover the UK, with surface breeze convergence zones triggering heavy showers and a few weak thunderstorms.
... E SCOTLAND, N, CENTRAL & E ENGLAND ...
Cold mid-level temperatures below -20C at 500mb, in association with upper trough overspreading the UK, along with surface heating of moist airmass pooling across the above areas, will create steep lapse rates that will yield 200-500 j/kg CAPE with peak heating this afternoon. Surface breeze convergence inland from E Scotland down through Northern, parts of central and eastern England towards the south coast today will be the focus for stronger updrafts with isolated risk of thunder amongst scattered showers, some heavy, developing across the above areas this afternoon. Cells will be slow-moving due to slack winds, so there is potential for some localised flooding where heavy rainfall persists.
Issued by the Netweather forecast team whenever there is a risk of storms or severe convective weather, these discussion based and in depth forecasts will highlight the areas at risk and give an in depth description of the risk and the factors surrounding it.
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.