A cold weather warning has been issued for Norfolk by the UK Health Security Agency.
The Met Office and the agency say a cold snap will hit the county between 6pm on Sunday and 6pm on Tuesday.
At night, temperatures could plunge as low as -3C in rural parts of Norfolk, but daytime temperatures are not expected to fall below mid-single figures during the chilly spell.
Toward the south of the county, Thetford and Diss are expected to fall to -2C on Monday night, whereas areas like Cromer and King's Lynn are likely to hit -1C.
Norwich is also likely to record -1C temperatures in the early hours of Tuesday morning, according to the Met Office.
Pensioners and people with underlying health conditions have been urged to keep their heating on at least 18C, while people should stay warm and look out for those who are most vulnerable in cold conditions.
Dr Agostinho Sousa, consultant in public health medicine at UKHSA, said: “Cold weather can have serious consequences for health, with older people and those with heart or lung conditions particularly at risk.
“It’s important to check in on family, friends and relatives who are more vulnerable to the cold weather.
"If you have a pre-existing medical condition or are over the age of 65, it is important to try and heat your home to at least 18C if you can.”
David Oliver, a deputy chief forecaster at the Met Office, said: “From Sunday and into early next week an area of high pressure will dominate the UK’s weather.
“This will bring some cold nights with a widespread frost across the country.
"However, by day temperatures will recover to around mid-single figures, near normal for the time of year.”
The UKHSA said if people can’t heat all the rooms they use, they should heat the living room during the day and the bedroom just before going to sleep.
People should wear several layers of thinner clothing rather than one thick jumper, it added.
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