...To georeference the images I need the geographic coordinates so that any pixel position on the map determines the true geographic position.
However, when I download a synoptic chart from DWD Wetterzentrale or UK Met Office for example, the geographic coordinates are lacking.
Yes, you are correct, the georeferences have to be shown on the image in order to use the Overlay Wizard, successfully. Often times these references
are not completely clear, or you have to use a coordinate line that is not optimal. Sometimes you have to just try it, determine how it overlays and then just try again. However I would bother using images that do not have the coordinates shown, and clearer the coordinates are, the easier it is to get it right the first time.
This is the first time I have heard that DWD Wetterzentrale or UK Met Office do not have the georeferences!!
You had best go after them to get those back, and I hope everyone will pester and persist until they show clear georeferences. That is a disservice to all.
In answer to you last question. Is there a place to download met maps that are automatically georeferenced?
Yes, weatherfax should generally be updated at least every 3 months and this should be maintained by the users, but is not.
David, Hwe and I updated weatherfax not that long ago, but the weather
services keep changing.
Perhaps a group of clever users should get together and update all of the weatherfax urls, or at least the ones in their section of the world, and then send the changes via the Cruiser Forum designated Weatherfax thread (not this one!)
Also reading that thread will give you more insight.