North-east US braced for huge snowstorm
A "potentially historic blizzard" could dump up to 90cm (3ft) of snow on the US north-east coast, the National Weather Service (NWS) has warned.
New York Mayor Bill de Blasio said the storm could be the city's biggest ever, telling residents to "prepare for the worst".
Heavy snowfall is forecast from Philadelphia to Maine. More than 3,000 flights have already been cancelled.
A blizzard warning has been issued for New York and Boston from Monday afternoon until Tuesday.
BBC Weather's Sarah Keith-Lucas explains the causes of the expected adverse conditions.
26 Jan 2015