Weather.com <--- the most accurate across the world. The reason I say this is because of the following- like all weather sites, they use data provided by the US Government. But they also add some of their own data from smartphone apps, commercial sources and aircraft , plus data from Euro government sources. They also track data on past predictions and actual weather conditions, and compare this to other sites to try to beat the accuracy of official government sources. The amount of computing power allocated to NOAA and associated weather orgs is astounding, to which IBM (the parent company of Weather.com) adds even more.