While I don’t understand the mechanisms behind it best, but Raleigh is wetter and stormier a bit than Charlotte in summer. Further east and south you are the bigger the summer precip maximum is, further west and north less.
81-10 RDU precip J/J/A 12.51
81-10 CLT precip J/J/A 11.64
The difference is really pronounced where Raleigh peaks at almost 5 inches in July where as Charlotte is at a minimum for the summer under 4 inches in July. 91-20 is really interesting the summer precip maximum is much more pronounced in Raleigh which goes along with a warming world . Also, looking at other stations around Raleigh seems RDU is a bit of a dry spot , most in the triangle seem to average 45-46 inches of rain annually whereas RDU is 43.
Raleigh is also more humid and a bit hotter than Charlotte , plus higher dews here.