The addition of the optional GXM 40* antenna to a compatible Garmin GPS, will provide real time weather forecasts, XM radio, and real time traffic information. You can see what the weather will be like along your route or at your destination. With the GXM 40 and the monthly subscription from XM you can view current weather conditions, city forecasts and thunderstorm, tornado and flood warnings, right on the units display. You will have hundreds of available XM radio channels. You will also have real time traffic data that the GPS will use to route you around delays.