The only time it really has an affect is when it is a HUGE eruption. Like Krakatoa or Mt. Pinatubo. For example, Mt Pinatubo's eruption emitted more than Mt. Saint Helen's eruption, but it only reduced the average global temperature by 0.9 degrees Fahrenheit in 1991.

I remember when Mt. St. Helens erupted back in 1980, my college roommate's family owned a wheat farm in Ritzville WA. where a lot of the ash collected. In the low points in his fields the ash layer was several feet thick. He was worried that his crops would be destroyed, but the wheat grew thicker and better in the deep ash than ever before. He enjoyed great crops and extreemly high soil fertility for years. I know this has nothing to do with the Carolinas climate and ash blown high into the atmosphere, but it is an interesting thing to think about.