Tomorrow at 2:21 p.m. Central, is the moment of the Autumnal Equinox. At this moment, the sun will be directly above Earth's equator, moving from north to south. Day and night are approximately of the same length all over the world. Day length has been steadily shortening and at an increasing rate, since the Summer solstice back in June. From this point until the Winter Solstice on Dec. 21, the length of daylight will continue to decrease each day, but at a slowly decreasing rate.
The decrease in solar radiation will result in colder and colder weather, although the temperature drop through the fall season is never a steady drop owing to the natural variability produced by weather systems. Other than the gradual, irregular descent into winter, there is no actual weather specifically related to the Autumnal Equinox.