Weather experts said that the snowfall that settled on Central London yesterday came after a week of cool winds had countered the city’s naturally warmer microclimate, known as an urban heat island.

The capital has also been without the “duvet” of nightime cloud cover during the period, which normally contains the extra heat that the city generates from energy usage. Instead, the heat has escaped out into space, leaving cooler conditions more suited to settling snow.

Brian Hoskins, a Royal Society research professor based at the University of Reading’s department of meteorology, said that various factors had conspired to create the uncharacteristic snowfall.

He said that a particularly stubborn high-pressure system, which is sitting over the country, was blocking the warm, moist winds from the subtropical Atlantic from reaching Britain. Instead the high pressure was drawing icy winds down from Russia through the Baltic, sending the temperatures plummeting.

Professor Hoskins said that the winds had “equalised” London’s status as an urban heat island, and had left it with temperatures little different from neighbouring areas of the country.

“A city like London gets heat from all the activities that occur, such as traffic and the energy used to warm all the houses,” he said. “It all goes into heat, which warms up the surroundings.

“But London now is not very different from the surrounding country. It has been made cold enough by the wind over the last week. The ground has been cooled down. Normally if the ground is slightly above freezing then the snow would hit it and turn to slush very quickly.

“Instead the ground has been cold enough to allow the snow to settle as snow.”

The urban heat island effect, which can make a city up to four degrees warmer than other areas in the country, is most pronounced when winds are low.

Meteorological phenomena associated with the heat islands include summer storms, when the extra heat can be enough to trigger thunder and heavy rain.

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