US north-east shivers in snowstorms
The US north-east is reeling from the latest in a series of blizzards, with low temperatures - up to 17C below normal - exacerbated by strong winds.
A fourth major snowstorm in Boston, Massachusetts, made February the snowiest month in the city's history.
Almost 2,000 flights have been cancelled so far, mostly from airports in Boston and New York.
Heavy snow and freezing rain is also forecast further south, in the inland states of Indiana and Kentucky.
The separate weather system developing in that area is expected to travel eastwards this week, bringing further snow and sub-zero temperatures to the north-east.
Nearly 2ft (60cm) of snow was reported in parts of New England after the latest storm this weekend. Meanwhile, 13in (33cm) of snow was recorded in Boston.
It means Boston has been covered in 2.44m (95.7ins) of snow since the start of the winter, most of that in the last three weeks.
On Sunday , Mayor Marty Walsh said simply: "I don't know what to say to anybody anymore. Hopefully it will stop eventually."
The bitingly cold weather in the US north-east and Canada is expected to continue well into March.
According to Peter Sloss, duty forecaster at the BBC Weather Centre, the prolonged cold conditions are the result of a variation in the movement of the jet stream, a high-altitude ribbon of cold air that would usually be expected to travel from west to east.
This year, however, the jet stream has followed more of a north-south route, bringing Arctic air deeper into the US and Canada.