Fall is the time of the year for drastic changes in the weather. The colder drier air associated with the Arctic Front is dipping farther south from Canada into the northern United States.
As this Arctic air moves south, it pushes the warm moist air from the Gulf further south into the mid-Atlantic states. This transition from warm moist air to colder, drier air continues well into December, when the Arctic Front positions itself over the central portion of the country.
On or about September 21, fall begins in the northern hemisphere. This is the time of the year when the Sun is directly over the equator. This is called the Autumnal Equinox. At this time, the daytime and nighttime are each 12 hours long throughout the world.
From September 21 each day becomes progressively shorter until on or about December 21. At that time, the Sun will be located over the Tropic of Capricorn in the southern hemisphere at 23' 27" south latitude. That time of the year will known as the (Winter Solstice).Winter begins in the northern hemisphere. Summer begins in the southern hemisphere.
When looking at the Sun, it appears to be moving in the sky. The Sun does not move, it is the Earth which is orbiting the Sun and changes its location daily in its relationship to the Sun. The Earth's speed is 66,000 mph in its orbit around the Sun.