A powerful aspect of SiriusXM is it is a broadcast of real-time weather, like a movie. And because it’s satellite generated, it works hundreds of miles out to sea and updates constantly. A second source of data, NOAA weather files, requires Internet access. This data, delivered as compact GRIB files, presents a snapshot of conditions, and updates only when you download another one. The advantage is that these files are free. Various suppliers offer their own version of these files, such as Jeppesen’s C-Weather, which is what Standard-Horizon CPN plotters support, offering a five-day weather forecast updated every six hours, wind direction and strength, wave height and direction, ground temperature, humidity and visibility in miles. Not all plotters support GRIB file display.