If you don't have an airave at your home then more than likely one of your neighbors around you does and its signal is stronger than the tower.
The HTC sense weather pulls the weather data from the nearest tower (NOT GPS), but since the airave is essentially a VOIP, the erroneous weather data that you are getting is coming from the ip address that the airave is associating with when it transmits your info over a broadband connection to the next tower.
An easy way to find out is just dial *99 send while you are at home. Depending on which airave is nearby, you will hear a tone and a message "you are now within airave coverage". No tone or message, then something is wonky with the tower.
Don't worry if you are associated with an airave as you will not be charged for using it. Sprints default setting is to leave them "open" as a way of increasing coverage. I locked mine down after I was noticing my broadband speed dropping off. Both my neighbors have sprint and were happily getting good coverage via my airave...until I restricted its access.
Hope that sheds some light.
Kind of funny... I was saying this over a year and a half ago when it started happening to me and everyone argued with me about it saying it wasn't possible. Now, it seems like the first thing people say when someone posts that theycan't get the weather to update or they pull a far off city in.
David