-- Many residents in the South woke up to freezing temperatures Thursday morning, as lingering cold weather stretched across most of the eastern U.S.
That's because the jet stream has dipped so far south that it has reached the Gulf Coast and cold air from northern states has been able to move south into tropical areas like Naples and West Palm Beach.
Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere that follow the boundaries between hot and cold air.
The winds in jet streams blow from west to east, but the flow often shifts to the north and south, according to the National Weather Service.
Storm paths often follow the jet streams on the surface.
If a storm is strong enough, it can grab the cold air from the north and bring it down south, even to the Gulf of Mexico, where it was so cold Wednesday that steam was seen rising from the water near Destin, Florida.
ABC News' Morgan Winsor contributed to this report.