Jet Streams

A river of fast flowing air in the upper atmosphere is known as a jet stream. In the northern Hemisphere, the jet stream flows along the polar front and are generally 10-12 km high, with winds moving at 200-250mph. In the winter, jet streams bring stronger winds that dip further south.

If the jet stream is north of you, you experience warm temperatures.
If the jet stream is south of you, you will experience colder temperatures.