So it updates weather for some cities? If so, have you deleted the ones that don't update and then added them again?
Sometimes Yahoo weather stops updating for certain areas. This has happened multiple times in my area. Once, it got stuck at 99°Fahrenheit and sunny for about three days, and another time it was stuck at 53°and dark for about
four months.

The closest cities that had accurate weather were about fifty miles away. I had to rely on apps that didn't use Yahoo weather while I waited it out.