There is no official definition of an "Indian Summer", but the accepted requirements for an Indian Summer are as follows:
1) Period of warm, sunny weather. (check)
2) Temperatures above 70 degrees. (check)
3) After a widespread freeze/killing frost. (check)
4) Before our first snowfall. (check)
Looks like we have passed the test, with our afternoon temperatures expected to be in the low to mid 70s through Friday! Plus, last weekend we had a killing frost, and we haven't had our first snow yet. You can much more about Indian Summers here.
Find more history like this...
"Indian summer is first recorded in Letters From an American Farmer, a 1778 work by the French-American soldier turned farmer J. H. St. John de Crèvecoeur (a.k.a. Michel-Guillaume-Jean de Crèvecoeur):
"Then a severe frost succeeds which prepares it to receive the voluminous coat of snow which is soon to follow; though it is often preceded by a short interval of smoke and mildness, called the Indian Summer."
The moral of this Indian Summer story is, enjoy, because you know what's next!