iGrib is a GRIB (GRIdded Binary) file viewer for iOS (iPad, iPhone and iPod Touch).
This allows you to see the same data that the professionals use for forecasting.
This app is particularly valuable for people like sailors who require a longer range forecast. (The author is a sailor)
Grib files are available with up to 10 days forecast of temperature, wind, cloud cover, precipitation, pressure, relative humidity and CAPE - for various regions covering most of the world. Alternatively you can define your own files from within the app or use files from 3rd parties.
View one or more parameters at a time on the map, or touch and hold to see all the data for a particular point.