Ohio and ukiah, california, lie on the same latitude. however, ukiah has a moderate climate, while ohio has an extreme climate. what could the reason be for the difference in climate?

Places far from the equator are places at high latitude and places close to the equator are places at low latitude. The lower the latitude the warmer the climate. Latitude is an important factor that determines the climate.  But there are many other factors that determine the climate: distance from the ocean (Cities close to the sea or ocean will enjoy a more equable climate and inland cities which are far from the sea or ocean will experience extremes in temperature), elevation, the altitude.. The distance from the ocean is the reason why Ohio has an extreme climate.