Rising temperatures in parts of Norfolk and Suffolk made it feel more like May than February.
At Santon Downham, in Suffolk, the temperature on Wednesday afternoon reached 18.4C - making it the warmest day of the year so far.
Dan Holley, from University of East Anglia-based Weatherquest said that was more than 10C above the February average of 7.8C.
He said: "We've only recorded 18C or higher during the month of February in six of the past 40 years."
Those years were 1990, 1998, 2004, 2012, 2019 and 2021.
Other highs in East Anglia on Wednesday afternoon included 17.9C at Weybourne, where the February average was 7.1C and 17.2C at Marham, where the February average was 7.4C.
Forecasters at Weatherquest said the weather on Thursday would start off cloudy, with a band of patchy light rain or drizzle spreading eastwards across the region.
It will turn drier from the west later, with spells of sunshine, with light to moderate west to southwesterly winds and a maximum temperature of 13C.
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