Why have a 10 or 16 day forecast if the predictions change every day? Good question.
If you're planning something 10 days out, you can look 10 days out:
I did exactly this for my wedding. I watched the weather 7-10 days out on a website called http://www.metvuw.com. It was a high pressure system, but windy. So we could plan our dry weather venue and not worry about our wet weather plan B.
After the wedding I thought this would be a good app and WeatherBomb was born six years later.