I used to get all of my weather from TV, then I switched to Weather.com , then my brother, Andrew, told me that Accuweather was more accurate, so I had to switch. Well it was partially because their page loaded faster, too.
Next my daughter, Kimmy, told me her teacher had proclaimed Wunderground.com the most accurate. I like their easily accessible sunrise and sunset data. It comes in handy when you have to be out riding early or late. But I digress.
Everyone has an opinion about whose weather forecasting is the best. Now there's a site that can settle the dispute with real data, Forecast Advisor. Here's a brief description in their own words.
"ForecastAdvisor will also show you the accuracy of the major weather forecasters, including Accuweather, Intellicast, MyForecast, The Weather Channel, and the National Weather Service. We also provide links to your city's weather forecast at all the other weather forecasters, so you can compare for yourself."
This doesn't settle the assertion about Wunderground, they didn't make the cut. But is does demonstrate that the differences in accuracy between the top sites can be quite significant. If you try weather for cities in different parts of the US, you will see the forecasts are more or less accurate. Honolulu or San Diego weather are easier to predict than East Lansing or Cleveland.