If you are contemplating going out to view the Atlas V launch of the OTV-3 space plane today then by far the best place off Cape Canaveral AFS property is going to be Playalinda Beach. This will give you an unobstructed view of the launch pad from a distance of about 5 miles. The beach closes at dusk so there will not be a problem as dusk today is well after the launch window closes but do check before setting up.
To get to the viewing point you will need to cross Max Brewer Bridge and go all the way down the road, past the KSC northern gate, to the beach. You will have to turn north for a way until you reach the first parking lot.
Park up and then cross the sand dunes to the beach. Head south on the beach for about 3/4 of a mile until you reach a fence. This is the NASA KSC boundary line and the closest you can get to the launch pad.
Looking south you will see LC-39B almost demolished, then LC-39A and the next pad round is LC-41 which is where the Atlas will launch from.
A detailed map of the beach can be found here. The parking lots are the white rectangles and the viewpoint for the Atlas V launch can just be made out by following SR-402 out to the ocean.
However with inclement weather predicted there is no shelter on the beach so it may be best to select one of the alternate viewing sites. These are both accessible with no walking so you can stay in your car right up until launch.
Other viewing spots follow:
If the beach is shut or not appropriate for you then alternate viewing points are on the SR-401 behind Port Canaveral cruise docks where the launch complex is just over 11 miles away. There may be a few issues with buildings blocking the view of the pad from there, but a good view should be available if you move around a bit.
Failing that then the Max Brewer Bridge can offer a good view of the launch from the top of Titusville. It is 13 miles from the launch pad so the sound of the launch will not be great, but with the elevation you should be able to see the pad and get a great view of the launch. The pad should be lit up with Xenon spotlights, but if you look about half way between the VAB and LC-39A you should be able to see the LC-39 viewing platform and just to the left of that but further back is LC-41.