NOAA is much more localized than that, by a great deal. I set our location on the map and it covers about 1 square mile with my house in the center. The forecast is interpolated from data from a weather monitoring station at a local airfield just 5 air miles away, as well as broader geographic data points.
In my experience, the forecasts are more accurate than any others I have used, especially 3 to 4 days or less out. But I have not tried WeatherUnderground...I'll give that one a look.