NON-EXPERT OBSERVATION. Back when Doppler radar imagery online was new (1990's) the opposite was true: there was frequently a lot of signal in the town itself, but not outside it [this was when I lived in Texas] Later, signal processing methods appear to have been developed to reduce radar "clutter" in Doppler imagery which arises from the landscape and not the atmosphere. https://ieeexplore.ieee.org/document/1460942

So we may be looking at an artifact of "subtracting" baseline noise from the radar return over the city. During those years in Texas, if I really wanted to see what was happening in our city, I had to examine the radar result coming from a different radar station in another city.