Today is set to be the hottest day of the year so far, with temperatures “well above average” the Met Office has said.
After a warm spell earlier this month, the weather took a chillier turn.
But later today temperatures look like they could rise as high as 21C (70F) in places.
Check the forecast where you are
Sky News weather producer Jo Robinson said: “It’s the spring equinox – the first day of the astronomical spring – and it’s likely to be the warmest day of the year so far.
“It’ll be warm and sunny just about everywhere Thursday afternoon, with 21C (70F) possible in the south.
“There’s a small chance that 22C (72F) could be seen.
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“London, the Home Counties, the south Midlands, western areas of East Anglia and parts of the West Country look most favoured to see temperatures above 20C (68F) today, perhaps even the west coast of Wales.
“Anything above 19.7C would be the highest temperature of the year so far.”
Parts of the country are expected to be hotter than Barcelona in Spain and Athens in Greece – with highs of 15C and 12C expected respectively.
The highest recorded UK spring equinox temperature was 21.5C (70.7F) in 1972.
Earlier, people gathered at Stonehenge at sunrise to mark the equinox.
The warm weather is down to a high-pressure system to the east of the UK which is currently helping draw warmer air north across the country.
Thursday’s sunshine could be broken by some cloud in central parts of England.
A wetter weekend
Moving into Friday and the weekend, the weather is expected to be more unsettled.
While the last day of the working week will remain warm for many, some will experience rain moving in from the southwest.
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Sky News weather producer Jo Robinson added: “Friday will bring some rain to the west, but the warmth will hold on across much of Britain.
“More cloud and a strengthening wind mean temperatures probably won’t be quite as high as today, but 20C (68F) is still possible somewhere across an area from northwest Scotland to southeast England.”
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She added: “The weekend will bring more widely unsettled conditions, with temperatures lower than previous days, but perhaps still a little above average.
“There’ll be some milder nights too, with only a limited frost.”
Meteorological spring always starts on 1 March while astronomical spring begins around 20 March each year.
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The former is based on the annual temperature cycle and the latter is based on the Earth’s position in relation to the Sun.