Here in Boston, we’ve just had two hard frosts (nighttime temp < 25 f). However, this week, it is warming up! the southwesterly airflow is displacing the canadain high=ptessure system 9AKA the “Montreal Express”); and by Thursday, we should see highs in the 70’s! Is there any meteorological evidence for “Indian Summer”-did the native americans tell the colonists that they could anticipate a warm period (after the first frosts)?
It’s my understanding the the term "Indian summer’ comes from the old-fashioned equating of “Indian” with untrue (like in the term “Indian giver”). So an Indian summer is a false summer.
Although, when I Google, I see debate over this origin. This cite supports it yet the National Weather Service article doesn’t mention it.
On second reading, did that actually answer your question? I’m sort of unclear what you’re actually asking.
In my opinion, Indian Summer happens in September and October. Right now, we’re in “bonus time”. 
While I don’t know about the etymology of the words, I recall from living in colder climes that Indian Summer happens in September or early October. What you’re getting right now is commonly referred to as “lucky”.
Here in Southern California, we get Indian Summer during Oct & Nov, but we don’t call it that. We call it “Fire Season”.
Indian summer in September? That doesn’t make sense to me. September is still “offically” summer in the U.S., and often has plenty of hot weather that’s essentially a continuation of August.
My understanding of Indian summer is balmy weather that comes after some noticeably cool fall temperatures. Generally this would be in November (this might vary with locale), occasionally perhaps late October or early December. It feels summer-like in comparison to the colder weather that preceded it (and will certainly follow it). It doesn’t necessarily happen every year.
When Cecil said “pernicious anemia,” he probably meant “pernicous amnesia?”
I had always thought Indian summer was any warm period after the first frost. That being said I never thought of using the term in January or February.
A period of warm weather in January, is called the January thaw.
Zombie summer?
<mod>
Lately we’ve had lots of RAAAAAAAAAINS! here…
Zombie. Closed.
</mod>