I noticed last night that my city of Hilliard, OH was now showing up in the HTC Weather App. However, my work city, Westerville, OH is not showing up, but in its place I see Columbus, OH which is the main city of which Westerville and Hilliard are suburbs. On my Droid both Hilliard and Westerville came up whenever I was in those cities. I saw a note on the web of how to add a city to the HTC Weather - but I think it was an old note. Does anyone out there know how to add a city to the Thunderbolt's implementation of the HTC Weather?
The city that shows on the weather/clock widget gets it's city based on what is programmed at the tower you hit. You may be hitting a different tower with 4G than what you did with 3G. Force the phone to 3G and refresh the weather info and see if it changes to Westerville.
Mine does not work correctly either. But, I do not believe it has anything to do with the tower you hit. Mine is giving me weather for a town 150 miles from home. Every now and then it does get my home town right. I went to bed one night at home with the phone on my bedside table, and woke up with the phone in the same place, but I was 150 miles from home and it was raining!