The best rule of thumb for running attire is to dress as if it is 20 degrees warmer out than it is.

Not sure how cold it gets there, but when I lived in VA I was usually fine running in a half-zip tech shirt or a long-sleeved tech shirt until it got below, say, 30. I ran a race in 22-degree weather in tights and a loose long-sleeved tech shirt with ($8 asics) arm warmers underneath. I figured I could pull them off if it got too hot, but it was perfect. I've also done a run in CO with a sleeveless shirt and arm warmers when it was around 30 out.

For walking, I might add an extra layer or a vest. Possibly for running, too, depending on your speed and comfort. I was running my butt off for that race and if I'd even needed to stop and walk I might have been too cold.

It never hurts, if you are doing an out-and-back someplace safe, to overdress a little and stash your extra layer someplace you can come back and find it. You'll get the feel for what's comfortable for you soon enough!