Typically, such storms originate as a low-pressure area that forms within of the shore between North Carolina and Massachusetts. The precipitation pattern is similar to that of other extratropical storms. Nor'easters are usually accompanied by heavy rain or snow, and can cause severe coastal flooding, coastal erosion, hurricane-force winds, or blizzard conditions. Nor'easters are usually most intense during winter in New England and Atlantic Canada. They thrive on converging air masses—the cold polar air mass and the warmer air over the water—and are more severe in winter when the difference in temperature between these air masses is greater.