Climatology is - by common consent - a pain in the @rse.
Mosspigs is right, the crammer will give you what you need for the exam. Fortunately, there weren't that many questions on Climatology in the actual exam - there was much more emphasis on things like clouds (particularly CBs) and TAF & METAR decodes.
I know it's easy to say don't worry, but really - don't worry.