UK weather: Why has May been so wet?

More downpours expected in coming days

Matt Mathers@MattEm90
Wednesday 19 May 2021 15:14
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London and parts of southern England were hit with torrential downpours and thunder on Tuesday as this month's dire weather showed no signs of letting up.

More rain is expected in the coming days, in what forecasters have described as a wetter than average May.

According to the Met Office, May 2020 was the sunniest calendar month ever, with Britons enjoying 226 hours of sunshine, beating the previous record of 265 set in 1957.

It is now unlikely that we will hit those heights again this year. So why has May been so wet, and when is the weather likely to improve?

Not in the immediate future. Rain is expected to fall in vast swathes of England on Thursday and Friday and there is a chance of showers developing on Saturday.

April was described as “remarkably dry” but May appears to be making up for that deficit - in buckets.

BBC weather forecaster Ben Rich says the soggy conditions experienced so far in May can be attributed to the jet stream, a narrow zone of high-speed winds about 30,000 feet up in the earth's atmosphere.

"In April, the jet stream was weak, and remained well to the south of us," Mr Rich explains. "High pressure developed close to the UK and became persistent, blocking the progress of rain-bearing weather systems.

"But as April turned to May, that blocking area of high pressure drifted away and settled over eastern Europe."

As a result, the jet stream strengthened and shifted northwards, directing Atlantic low pressure systems across UK shores.

"At the same time, a dose of strong May sunshine has injected energy into the atmosphere - and combined with low pressure overhead that has led to very unstable conditions with air able to rise rapidly," Mr Rich adds.

"This has provided the perfect recipe for towering cumulonimbus storm clouds to bubble up, meaning the rainfall has often been intense and heavy, with hail and thunder mixed in."

Is the weather picture likely to improve towards the end of the month?

"As next week progresses there is a chance of more settled conditions to gradually become established," the Met Office says.

"Rain and showers are likely to clear away to the east, leaving drier and less windy conditions behind by the end of the week. Temperatures look likely to remain on the cool side, though feeling pleasant in the sunshine.

The Met’s 14-day forecast adds: "Night temperatures could become chilly, with late season frost in prone spots a possibility. As we move into the following week, things become more uncertain, but indications suggest a continuation of drier weather with the possibility of temperatures starting to increase slightly."

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