Erica's Answer:
Thunderstorms that flourish in the relatively low-lying, rolling hills of Lancaster County will sometimes get broken apart by the relatively higher terrain encompassing most of Chester County. And since Chester County consists of many more elevation changes than the area stretching between Lancaster and Oxford in Lancaster County, some thunderstorms just won't stay together. West Chester, specifically, is about 100 feet higher in elevation than the city of Lancaster, but there is even higher terrain just to the west of the city of West Chester.- Erica
