Temperatures are set to hit a sizzling 30C as the mid-summer sun bakes the county.
But forecasters say the hot weather will bring with it the risk of severe thunderstorms in the coming days with yellow weather warnings issued for both Friday and Saturday.
In Preston the mercury rose to 28C today and the thermometer yesterday and remained around 20C for most of the night.
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Britain recorded its hottest day of the year so far reaching 31C at Heathrow Airport. Lancashire was forecast to rise to 26C by 10am today to and above the 30C level by mid-afternoon.
People were being urged to stay cool and hydrated and not spend long in direct sunlight, with UV levels set to hit eight or possibly nine.
Met Office meteorologist Alex Burkill said: “That’s about as high as it gets in the UK.”
Shoppers queuing outside stores and supermarkets to maintain social distancing were being advised to take precautions as they could be exposed to the sun for a lengthy period.
Public Health England issued its own warning saying people who have been shielding, as well as old people, very young children and anyone with underlying health issues should take extra care. Others should make sure they check on vulnerable people through the hot spell.
The possible arrival of thunderstorms on Friday and Saturday could bring flash flooding and even cause damage to property, says the Met Office.
In Lancashire there is a 60 per cent chance of rain tomorrow. But the yellow weather warning means it could be heavy if it hits the county.
The downpours could lead to flooding and disruption, with lightning strikes, hail and strong winds also a possibility.
Temperatures are expected to drop to 24C tomorrow and then into the high teens on Saturday when more rain is forecast. By Sunday we could be back down to 16C.