Drawing outside is challenging! People are in constant motion, so you can't really draw purely observational. In a lot of cases you'll have to refer to what you know and just use what you see as the source of inspiration.
This morning I sat along a window where people were passing through the shop. So as soon as I looked at my sketchbook to put down my first line they were already gone.
Instead I tried to just observe them and make mental notes, and then try to do something based on those mental notes. I really don't know what I'm doing, which is why I should do it more often :P Remember the 10000 bad drawings rule!
And here are some posemaniacs 90 second drawings from 2 nights ago... it was actually a bad session...I think I've been doing those posemaniac sketches too often recently, and the brain just kinda becomes lazy then since there's no new input of information or new challenge.