Excellent, and very in
depth, on line class by Starpath.
http://www.starpath.com/marweather/marweather_title.htm
You can just buy the book, but its not nearly as good by itself. Way better to sign up for the class. Big comitment of time, but well worth it.
If you just want to learn to read a weather fax then all the symbology can be found here:
http://www.opc.ncep.noaa.gov/UGbegin.shtml
Good explanation of all NOAA/OPC weather fax products and explanation of abbreviations and symbology.