A question that gets thrown around via email to me from time to time and was recently posed via comment here is 'what does the definition of north and west' mean? Well, I thought I'd try to draw a little map and explain it. For those who are geography-inclined, bear with the lack of accuracy in the highway locations, thanks!
For starters, "Philadelphia" as defined in my forecasts is the area bound by the PA Turnpike on the north, the Delaware River on the east into south, and 476 on the west. Anything outside of that box fits into varying geographic locations based on direction away from the city.
I consider "north and west" of Philadelphia to mean locations that are west of 476 and north of the PA Turnpike in Pennsylvania, with the Delaware River being the eastern boundary of 'north and west' in Pennsylvania once you pass the PA Turnpike. The far boundary of north and west is Blue Mountain in Pennsylvania as that separates the main climate zone of Southeastern Pennsylvania from Northeast and North Central Pennsylvania on the other side of the boundary. When you see forecasts here reference north and west, I'm referencing not just the immediate north and west suburbs but also the farther regions as one heads out towards Allentown, Reading, and even Lancaster.
I drew about a line at about 30-35 miles outside of Philadelphia, roughly on a border between Quakertown, Pottstown, Parkesburg (Chester County), and Oxford (Chester County) as the border between the inner north and west and far north and west. In my daily forecasts, north and west covers regions on both sides of that 30-35 mile arc. In those regions there are some variable microclimates such hills in Chester County that are 800' above sea level, the Lehigh Valley, and others that allow for wide ranges of temperatures. However, typically the closer you are to Philadelphia the warmer the temperature usually ends up being. As you head out into Lebanon and Lancaster Counties the climates are closer to South Central PA than Philadelphia's far north and west...however, I do reference parts of both in the geographic area as Lebanon and Berks share similarities in weather and the eastern half of Lancaster and western Chester County are quite similar as well. I wouldn't be surprised if there were some arguments over Lebanon and Lancaster County...feel free to argue for its inclusion on either side of the line as you see fit.
The rest of the geography makes relative sense I would hope. I consider 195 as the boundary between north and east in New Jersey and south and east in New Jersey, with the Delaware River being the western boundary of that line throughout. Delaware falls in the south & east category as well.