For me, "sweater weather" refers to temperatures below 70 degrees - and if there's a drop from 100 to low 70's in any 24-hour-period that will probably feel chilly too.
Today is sunny and clear, too nice to crate Toby while I get my hair done. But the temperatures will start dropping this afternoon to the mid-30's.
It's sweater weather for Toby today. He'll find a sunny spot and be cozy on yard patrol. The sweater is mostly for my peace of mind, honestly.
And also because he looks darn cute in it.