Bingo, Bill. I was gonna elaborate that I had determined that cold was a factor. In fact, the first day I resumed running, I was wearing running shorts, got 4 miles from the house and my knees just locked up. I was a pitiful sight, limp-jogging and walking by the time I got home. Two days later, went out dressed warmer, some pain but no lock-up.
I think it's a combo of 'too much too soon' and temp, after a total hiatus. Adding a couple of miles on a treadmill before my weight training has seemed to help, along with my normal running plan, in just getting the mileage back up gently.
Thanks for the comments, everybody.