It depends entirely on the geolocation database being used to map your IP address to location. wttr.in seems to use https://www.ip2location.com/ https://www.ip2

It depends entirely on the geolocation database being used to map your IP address to location. wttr.in seems to use https://www.ip2location.com/ https://www.ip2location.com/ so maybe they have better mappings for your ISP. Bigger providers tend to use Akamai or similar.