You're overthinking it -- just get a jacket.

If you want to geek out about stuff like that :-) the recommendations depend on how heavily you sweat and so how good must your clothing be at getting rid of excess moisture produced by your body. The usual recommendations here go along the lines of "don't wear cotton" (aka "cotton kills") and "have a breathable shell".

In the case of Baltimore, if you don't anticipate walks in the rain, get a fleece and a down jacket, zip up or unzip as needed. If you do, you'll need a waterproof shell (Gore-Tex or equivalent). Or an umbrella.