Weather updates from site founder Brian Gaze that keep you in the know.
Posted Mon 21st May 13:47
Warm weather continues in the approach to the Bank Holiday weekend but will be a risk of downpours and thunderstorms in the south. Next week the mercury may climb even further.
Upper air level temperatures over the UK are significantly above the 30 year average and that likely to remain the case throughout the next 16 days. That's an impressive run and there are signs of it becoming even warmer next week.
The London GEFS 6z plot below shows the 850hPa temperature mean of between 5C and 10C in the short term but it climbs above 10C next week. A few of the individual runs have values approaching 15C and if that happens we could see temperatures pushing up towards 30C (86F) at the surface level in southern regions if there's enough sun. The word "heatwave" would need dusting down.
Despite the warmth it's not necessarily going to be dry all of the time. High pressure is centred to the north of the UK and areas or low pressure remain over France. Therefore showers and thunderstorms could be an ongoing risk.
Today's GFS 6z shows one of the warmer outcomes on offer. The chart below is for Sunday 27th May and although it's warm the real heat is sitting to our south. The 10C 850hPa border is just to the south of London. As a rough guide you can add 15C to calculate temperatures possible at the surface level in sunny periods, but during cloudier or wetter spells the difference becomes less.
By Tuesday the warm air mass has pushed northwards and the 15C 850hPa line edges into the south eastern corner. The GFS 6z run has core of the heat just to the east of British isles but it wouldn't take much adjustment to see our weather moving from the warm / very warm category into the hot one.
The set-up is quite unusual for the UK. Allegedly King George II said "the British summer is three fine days and a thunderstorm". That is usually not a bad characterisation but on this occasion it looks as though thunderstorms won't mark the end of the warm spell.
A lot of warm weather is expected in the run up the Bank Holiday. Next week temperatures could rise further as a "blowtorch" pattern sets-up and a plume of air southern Europe pushes northwards. However thunderstorms may continue to break out during the days in southern and central Britain.
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