When the National Weather Service issues a forecast, do they try to make it as accurate as possible for the weather station where they take the measurements, or for the city/metropolitan area that that station represents?
E.g., in Chicago the NWS station is at O’Hare airport, which is consistently colder during the winter than most of the city. Now it may not make that much difference on most days, but if they are on the borderline of predicting a high in the mid-30s vs upper-30s, do they try to predict the temperature they will record the next day at the airport, or the temperature the average Chicagoan will experience?
While NWS may be located at ORD, don’t assume that all weather forcasts for Chicagoland are based on a single station. The NWS current conditions reports for Chicago list ten different stations in the area.
The temperature “number” that is forecasted relates to the “official” weather station, so in your case that would be O’Hare. See this as an example. It even gives the coordinates for the forecast point in the upper left part of the page. That is known as the “point” forecast. The regular forecast is paragraphs of text and usually addresses the variables. Where I live we regularly get twice as much snow as people still in the Denver metro area that live only 15 miles east of me. South of town is a ridge called the Palmer Divide which is barely noticeable to the eye but can have a huge influence on the weather, as anyone driving between Denver and Colorado springs in a snowstorm can attest to.
Snowfall forecasts here are usually given in three locations - East of I-25, West of I-25, and In the foothills.