Tornado and storm researchers have issued a severe weather warning for Hertfordshire tonight.

The Tornado and Storm Research Organisation (TORRO) said weather cells overnight between Tuesday, September 6 and Wednesday, September 7 have a "chance of producing one or two brief tornadoes" in the southern portion of England.

TORRO's weather warning - which also forecasts cloud-to-ground lightning and hail measuring up to 15-20mm in diameter - covers all of East Anglia, the South East, the South West and Wales.

It also includes the East and West Midlands, Hull, Manchester and Liverpool.

The TORRO forecast reads: "A messy picture for Tuesday and Tuesday night, with a vertically-stacked low close to south-west Ireland."

A vertically-stacked low means the pressure is low at all levels in the atmosphere, which can cause "severe weather".

It adds: "Several shortwave troughs will affect the area through the period - one is moving into south-west England now and will move north-north-east, and another should cross at least central and southern parts of this area into this evening.

"Each of these will enhance the convection, perhaps introducing lines of showers and thunderstorms.

"Stronger cells have the chance of producing one or two brief tornadoes, especially for the southern half of the area. Cloud-to-ground lightning or marginally severe hail are potential hazards.

"Brief heavy rain is likely, too."

Another forecaster, the Met Office, has not issued any weather warnings for Hertfordshire.

Instead, a yellow thunderstorms warning is in place overnight in eastern Scotland, over Inverness, Aberdeen, Dundee, Edinburgh and Glasgow.

The Met Office's forecast features sunshine and cloud in Hertfordshire on Wednesday, and stormy weather in the county on Thursday.

Friday is set to bring some rain before a return to slightly drier conditions on the weekend.

The Met Office long-range forecast for the period Sunday, September 11 until Tuesday, September 20 reads: "Fine and dry for many areas to start.

"A band of cloud and rain is likely to move eastwards over the far southwest of the UK on Sunday, bringing some stronger winds here.

"Becoming more changeable again at the start of next week, particularly in the south and west, with cloud and spells of rain.

"Drier and brighter weather likely across the north, though rain is still possible here at times.

"Towards the end of the period, high pressure building from the southwest could gradually replace low pressure centred near the south of the UK.

"This would result in a mixture of showers or longer spells of rain and sunny periods.

"Temperatures largely near normal throughout but locally warm in parts of the south."