There are an overwhelming number of weather apps out there and when you find one you like you tend to get a bit biased. Here are mine:
My goto app is a grib downloader called PocketGrib. A free version is PocketGrib Lite and will download two days of grib files. The full version is four bucks and allows eight days of weather to be downloaded. For your file you can select resolution down to .25 degrees, interval of time down to 3 hours, up to eight days, and a mess of parameters that include: wind, pressure, air temp, waves, clouds and humidity. Once downloaded the data can be displayed on a map, meteogram which is basically a bunch of graphs, and the data tab that is in column and rows.
Raindar is my next app. This is an intuitive map and radar display. Zoom in and out with pinch and move around with ease. It automatically animates to give you a clear picture on when you are going to get clobbered. My boat neighbors think I have a sixth sense after they see me checking the anchor snubbing line and bringing in the cushions then 15 min. later we get hammered.
Weather Underground is a nice local weather app that includes some helpful features such as moon phase, sunrise and sunset times, and a easy to read forecast chart.
An honorable mention is this modeling website not an app at all, though there are similar apps they are not suited for mariners, the site stands out because it gives a great visualization of coming weather. It takes some fiddling with to get the most out of it but once you do, it will improve your sixth sense that much more.
These have been what I use when we are on grid, in a coming post I will write about my off grid system.