Weather maps need weather symbols, and until now the only choices for marker icons on Static Maps have been the regular Google Maps pins. Google announced that the “Static Maps API now supports custom marker icons. Just specify the URL of a PNG, GIF, or JPEG icon in the marker definition, and we'll fetch the icon and add it to your map. We'll cache the icons you specify to maintain performance, and even generate shadows for your icons if you wish: markers=icon:http://maps.google.com/mapfiles/kml/shapes/sunny.png|shadow:false. You can use up to 5 different icons on a single map, each of which can be used for multiple markers, so come rain or shine you can always take the weather with you,” revealed.
More info: Static Maps v2 API Developer's Guide