During Christmas 1927, heavy snow fell in the Cotswolds in central England, where the Thames has its source. A sudden thaw occurred over the New Year's Eve of 1928, followed by unusually heavy rain, doubling the volume of water coming down the river. The sudden rise in water level coincided with a high spring tide and a storm surge caused by a major extra-tropical cyclone in the North Sea. The storm surge raised the water levels in the Thames Estuary, measured at Southend, to 1.5 metres (4 ft) above normal.