Fall officially starts at 9:49 a.m. CDT on Saturday, September 22, 2012, when the sun crosses directly over the equator as it heads south to its winter solstice position. The sun crosses the equator twice a year- on the autumnal equinox and spring equinox.
In Chicago, it's felt like fall for the past week or so. And it continues into the weekend; cold, wind, and rain are expected for the first day of fall.
"73 and 52 are normal [high to low temperatures] this time of year. We will be nowhere near that high," ABC 7 Meteorologist Mike Caplan said Friday. "Saturday night into Sunday morning, almost guarantees you're going to have some frost as you get away from the city."
What do the cooler temperatures mean for those fabulous fall colors of red, orange and gold?
"That's good," Boyce Tankersley, director of living plant documentation at Chicago Botanic Garden, said. Fall colors are the result of trees and plants getting ready for winter. So when the temperatures drop, it signals it's time to go dormant, leaving the bright colors behind.
"Ideal conditions are bright, sunny days with cool nights," Tankersley said. The earliest trees -- honey locusts -- are starting to turn at the Chicago Botanic Garden, but the real show starts next week.
"We anticipate it's really going to be next week when we see the reds and oranges," he said.
And despite the really long, hot summer, Tankersley is anticipating "good" fall color. "Some trees dropped their leaves early. The trees that have leaves left will be very colorful."
"Our good fall color's going to run through the middle of October," he said.