"Indian Summer" is loosely defined as a period of unseasonably warm weather after a frost. This is certainly unseasonably warm weather we're having today through Thursday with highs 10-15 degrees above average in the upper 70s and low 80s. Look at the three maps below and track the warm weather as it gets gradually pushed to the southeast day by day.
Notice on the first map, we're still very warm with highs in the 80s even through the upper Midwest and Great Plains. Colder temps are in the Northern Plains and Rockies.
The second map shows the cold front dropping right over the Ohio Valley on Friday. Temperatures in the 50s have now made their way through Chicago and St. Louis. We'll have some showers with highs in the 70s.
The final map shows the front well to the southeast, with the warm air now squished down over Georgia and the Carolinas. Highs here on Sunday will only be in the 50s. It looks like the cooler air could hang around through much of next week.