April mini heatwave 2018 - how long we can expect warm British weather to last
Temperatures are set to soar to 28C (82F) in some parts on Thursday, making it the warmest April day in nearly 70 years.
The South East will enjoy the best of the weather, while most of England and Wales should see the temperature rise into at least the low 20s, the Met Office said.
Conditions will be mild across the UK, with Northern Ireland likely to push 19C (66F) in some parts and a peak of 20C (68F) possible in Aberdeenshire in Scotland, the forecaster said.
The hot weather far surpasses the average maximum temperature for April, which sits at 11.4C (53F).
The summery spell comes as a result of warm air from the Azores, off the coast of Portugal, being dragged up towards the UK by the combined efforts of an area of low pressure over the Atlantic and high pressure over western Europe.
The highest temperature of the year so far was recorded as 25.7C at Heathrow Airport on Thursday.
Met Office forecaster Graham Madge said the mercury was expected to soar past that later, pointing out that Wednesday's peak temperature was recorded at around 3pm.
He said: "We are not expecting that that is the maximum temperature - it will go higher than that. It is already warmer than any April temperature last year."
When was the previous warmest April day?
A high of 28C would beat the 2001 April high of 27.8C (82F), the Met Office said.
The warmest April day on record was 29.4C (85F) in 1949.
Meteorologist Alex Burkill said: "There's a fairly good chance of 28C, there's about a 60 per cent chance.
"Quite widely we are going to see low 20s, and for many it will be a little warmer than Wednesday."
Temperatures will climb even further tomorrow in the #sunshine, with possibly 27 ºC being reached somewhere in SE England, which will make it the #warmestdayoftheyear so far...again! pic.twitter.com/RBgPggGEf0
— Met Office (@metoffice) April 18, 2018
A high of 25.3C (78F) was recorded in St James' Park in London on Wednesday, making it the hottest day of the year so far.
How long will the warm temperatures last?
Thursday is expected to be the hottest day of the warm spell, with weekend temperatures dipping slightly before showery outbreaks on Sunday.
Competitors in the London Marathon can expect hot and humid conditions with a forecast of between 21C (70F) and 23C (73F), Mr Burkill said.
"There could be a shower but it's not very likely. It's not great conditions for running. In fact if any showers do come they might be very welcome," he said.
Hayfever sufferers hit by high pollen counts
Some hayfever sufferers could be affected by high pollen counts, he added.
Mr Burkill said: "For anyone who suffers from tree pollen they will probably be feeling the effects, but that's only about 20 per cent of hayfever sufferers. Grass pollen season comes later in summer."
Whilst pollen levels will be high across much of the UK, only hay fever sufferers who are affected by birch and ash tree pollen will feel the impacts �� pic.twitter.com/2vUHiqgtG7
— Met Office (@metoffice) April 19, 2018
Weather forecast for Thursday and the week ahead
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