The Tornado and Storm Research Organisation (TORRO) has issued a severe thunderstorm warning for Cornwall which could include tornadoes.

The Met Office has already issued yellow warnings of thunderstorms hitting Cornwall and the southwest this evening and the weekend.

However, TORRO has now issued a severe thunderstorm warning for the region and the south west.

It defines a severe thunderstorm as producing one or more of the following:

• one or more tornadoes and / or waterspouts

• hail with diameter of at least 20mm

• non-tornadic winds gusting to 55 mph or more at surface (but which are not part of synoptic-scale straight-line winds of such velocities)

It says thunder and lightning does not necessarily need to be present for any of the conditions listed above to occur.

“Showers and thunderstorms already across Kent/E Sussex will continue to move in a general westerly direction, and should develop further/expand in coverage into this afternoon, as diurnal heating erodes low clouds and allows 500-1000J/Kg of CAPE to evolve.

“Relatively low freezing levels may allow some marginally severe hail to develop in the stronger cores in and close to the depicted area, although coverage will - of course - be hit-and-miss.

“Rather humid low-levels should preclude too much in the way of strong wind gusts, but a few isolated gusts to 40-50mph are possible. Heavy rain is likely in places too.”

The Met Office says Friday and the weekend will see heavy showers and thunderstorms develop across southern areas, including Cornwall Yellow National Severe Weather Warnings for thunderstorms have been issued for Friday, Saturday and Sunday.

Met Office Chief Meteorologist, Jason Kelly said: “Thundery downpours have developed across parts of southern England, and will last into Friday evening, bringing frequent lightning, gusty winds, hail, and spells of heavy rain. The risk of thunderstorms persists into the weekend with potentially longer spells of heavy rain for some along with a continued risk of hail and lightning accompanying the most intense storms. Parts of the Midlands, southern England and east Wales appear at greatest risk of seeing these conditions.

“The warnings cover the areas of the country most at risk of seeing thunderstorms but not everyone within a warning area will experience a thunderstorm. For many much of the time it will remain dry.”

 

Met Office Deputy Chief Meteorologist Dan Harris added: “The area of persistent and at times heavy rain that we are expecting to have developed by the end of Sunday will most likely continue for some parts of southern UK through at least the first part of Monday, before starting to clear eastwards. By this time however, confidence falls sharply in terms of both its exact location, and rainfall amounts. We are keeping a further warning for Monday under review, so please keep up to date with the latest forecast for your area.”

This change to more unsettled weather will also see a downturn in temperatures beginning in the far north particularly as we head into the early part of next week.