Why does the flight time vary at different times of the year?
Flight times vary by season because atmospheric conditions, in particular wind speeds, effect flight times. The jet stream is an upper-atmosphere wind stream that blows from west to east. During the winter, the wind speed is much faster than during the summer months. As a result, traveling from east to west during the winter months will take longer than similar travel during the summer. In the reverse, traveling west to east in the winter months will be much shorter than during the summer.
