like most thngs in life..you got to pay for it..most forecasters know more than what they can fit in two lines of text below an icon. If your amped to go somewhere thats my suggestion.
But rule of thumb, 3-5 days in winter and 5-7 days in summer for reliable forecasts.
This is what I would read if I was interested in finding a pattern for about a week in advance.
http://www.atmos.washington.edu/data/disc_report.html