Answer:
a jet stream that brings alternating warm and cold periods
Explanation:
Jet streams are known as a composition of powerful wind that normally moves from west to east all over the world.
According to various research, it is considered strongest in winter, specifically showing a strong effect on weather in North America.
A jet stream at a normal pace is associated with normal cold and occasional warms, but at a strong pace, it usually creates heavy cold moving and warmth from north to south and vice versa. This is known as Rossby waves.
Hence, in North America, a winter weather change that might be associated with large amplitude Rossby waves is " a jet stream that brings alternating warm and cold period"