In the blog post, Getting Into The Forecaster’s Head, it was discussed that the weather forecast offices (WFO) are organized by county warning areas (CWAs) and forecasters are physically located in different buildings within these areas. Often these CWAs cross over state boundaries, but in many locations throughout the U.S. they do not (See image 1).
Image 1. CWA Map.
Meteorologists will attempt to coordinate their forecasts with bordering WFOs to avoid a forecast that appears to arbitrarily end at the state line or other geopolitical boundary, but that coordination doesn't always happen, which leads to forecasts that are aligned via geo-political boundaries.
Forecasts bounded by geo-political lines can also occur at times related to the issuance of AIRMETs/G-AIRMETs. On any given eight hour shift, there are three forecasters at the Aviation Weather Center (AWC) that issue these forecasts. There's one for the eastern region (BOS/MIA), one for the central region (CHI/DFW) and one for the western region (SFO/SLC). These meteorologists sit next to each other and some attempt to coordinate their forecasts, but this is not always the case.
Image 2 is an example of a Turb-Hi G-AIRMET where cross region coordination did not occur. Notice the western part of the G-AIRMET ends at the state boundaries.
Image 2. Turb-Hi G-AIRMET ending at geo-political border.