The Search Bar on your Homepage is pre-populated based on your IP Address or the last known search on that computer. 

Based on IP

Pre-population based on IP Address means the pre-populated location may not be the city you are in.  For example, you could be in Seattle WA, but the pre-populated location may be Tukwila WA which is about 25 minutes south of Seattle. 

Based on Last Search

If you search for a location from the Search Bar on your Homepage, then return to your Homepage you see that the pre-populated location changes to the location you searched for.  Each time you do a new search the pre-populated location will update to the most recent search location.