A major lake-effect snow event has hit the Great Lakes region of the US, causing intense and paralysing snowfall. It started on Wednesday evening, and will probably carry on until the end of the weekend with the worst-affected places being Buffalo City on the eastern edges of Lake Erie, and areas around Watertown on Lake Ontario. Lake-effect snow occurs when cold air blows across an unfrozen lake that is relatively warm, heating the cold air from below and creating heavy snow showers. These showers often form in narrow quasi-stationary bands causing significant amounts of snow to fall over a small area. This current event is caused by cold air sourced from Canada, blowing cyclonically around low-pressure located above the Great Lakes, becoming a returning south-westerly or westerly flow depending on location. One region commonly affected by lake-effect events is Buffalo, New York, and its surrounding area. Buffalo is located at the north-east end of Lake Erie, where these narrow trains of heavy snow showers, or even thunderstorms, often reach. Usually these snow showers are quite intense with the heaviest snowfall producing as much as 3-4in (7-10cm) an hour. So far, areas to the south of Buffalo have received 10-12in of snow by midday on Thursday. By the end of the weekend, these areas could see up to 4ft-6ft of snow. Coincidentally this snowfall event is likely to be the biggest since almost exactly eight years ago to the day, where Buffalo received 5ft of snow. Over the whole event, the affects will be more widespread than just the eastern flanks of Lakes Erie and Ontario, with heavy snowfall also being expected on the eastern flank of Lakes Michigan and Huron. In the UK, the low-pressure system that brought heavy rain and subsequent flooding in the past couple of days has also been responsible for high wind speeds in northern parts of France. As the system propagated to the north-east through the Channel, the strongest winds were recorded at Boulogne-sur-Mer, approximately 35km (21 miles) south-west of Calais, with a maximum gust of 70mph.