As discussed in this blog post, the precipitation forecast on the prog charts is issued by the local weather forecast offices (WFOs) throughout the country. The forecast is supposed to look seamless. However, it is not uncommon to see the resulting prog chart precipitation type forecast to follow the county warning area (CWA) boundaries when there's a difference of opinion as to the precipitation type expected. Here is such a case based on the difference between forecasters in the Mount Holly (PHI) , Sterling (LWX), and State College (CTP) forecast offices.
The precipitation type forecast shown below valid at 18Z clearly shows that for southern New Jersey, extreme southeastern Pennsylvania and the Delmarva Peninsula that rain (light green) is expected to reach the surface. This includes the city of Philadelphia. However, further west it is very clear that the precipitation type is expected to be either a mixed precipitation type (purple) or ice in the form of freezing rain or freezing drizzle (orange). This includes the city of Baltimore. But if you compare the line of demarcation between the two with the boundary of the CWAs above, you'll notice that one forecast office believes this will be rain and the other two believe it'll be some form of mixed precipitation or ice.
While there could be a meteorological reason for this abrupt change, this is not the case for this weather system. It appears that these forecast offices are not coordinating their forecasts as they should. In fact, it also shows up in the