Briara

Briara's followers consider thunder to be her voice. Most of the time she's talking, she's providing philosophical wisdom to humanity, but none know how to listen to her. 

Clerics and Paladins of Briara are supposed to, in a thunder storm, stop what they are doing and journal to write down what Briara is saying (or at least their best interpretation). Most of these clerics and paladins have their journals saved in a library, so there are many out there.

She's a retrospective-wisdom lighting goddess.