ooh! ooh! something I actually know something about! As an Accuweather professional subscriber, I can give you the scoop on the 15 day forecast... this applies to all long range forecasts
The 15 day forecast is generated by computer models. These computer programs take all exhisting data, and run a likely scenerio for upcoming weather. When predicting long range weather (ie 15 days out) even the slightest shift in current conditions can drastically change the outcome. Now, looking at the weather predicted just a few days out, the models tend to be more accurate. The models for this range of forecasting are run every 6 hours. Hence, a change in the forecast can occur every 6 hours.
So, what good is it? Well, you have to look for a pattern. Are the temps generally trending upward? Do more runs than not predict some form of precip? etc....
If you really want to know what the experts think about weather that far out, read their blogs/discussions. These can be found on Accuweather and NOAA.gov. On NOAA, for any location, on the bottom left of the page will give you several links, click on "forecast discussion".
oh, and your right, I'm a weather junkie
