I was driving home from work, down Concord Ave, around the Trader Joe's area. It is overcast, but light out still. I often look up, and saw a bunch of black dots. My first thought was birds, except there was a larger weird looking object with them, and they moved too slow to be birds, and weren't shaped right, and didn't travel like birds. I pulled over into a gas station parking lot, and got out of the car and grabbed my phone/camera. The larger object was shaped like a wobbly jelly roll, and all the rest of the objects were much smaller dots/circles. I first noticed the larger object tumble around in no noticeable direction, but it was not stationary. Then I noticed small black dots around it, then more and more. Two dots stayed ahead of the object, and the rest, about 15 of them or so, moved around, non-linear, but not stationary. They moved around each other. They were below and to the left of the larger object. After a minute, the small dots below the object faded. Not suddenly, but quickly. The larger object with the two dots in front of it stayed, moving off together. It was still moving off when I returned to my car and left. I did take a picture and a video, but not more because it was hard seeing the objects on my phone. One other lady saw me looking and stopped to ask me what I was looking at. She saw the larger object and wondered what it could be, but by that time the black dots were all gone.