Quite a shock is on the way this weekend. After a very pleasant spell the past few days, bitterly cold raw winds will sweep down from deep inside the Arctic. That could bring snow to Scotland, eastern England and even as far south as London. So much for springtime.

Much of the blame for this flip lies with the jet stream, a ribbon of wind a few miles high, which marks the boundary between cold Arctic air and warm sub-tropical air. At this time of year, the path of the jet stream tends to wobble around and, when it passes to the north of the UK, allows warm air to flow in. But this weekend it is taking a more southerly track, delivering cold air.

Wintry weather in April is not unusual, though. On April 26, 1950, a blizzard struck England especially hard in the South. Deep snowfalls brought roads to a standstill and Sevenoaks, Kent, was completely marooned. The snow was particularly damaging because it was wet. Telephone cables and poles collapsed, and a garage roof in Kent collapsed under the mass of snow, crushing several cars inside. But when a rapid thaw set in, many people had narrow escapes when melting snow slid off roofs in miniature avalanches.