In my intro ecology class at UW the Southern part of the state was considered Oak Savannah, and there was a line where it switched over to conifers. I haven't seen that type of terminology used since so I don't know if it fell out of fashion, but my recollection of the map was that it was more of a diagonal line, and wouldn't quite fit Hwy 29. Since I've gotten a cabin out that direction though it certainly seems like there are some noticeable precipitation differences north and south of 29.