If average temperatures from South Dakota were compared to temperatures from Oregon it would show that Oregon has warmer winters and cooler summers than South Dakota does. What accounts for why this is when they are at similar latitudes?

It is because Oregon is located near to the Pacific ocean

Explanation:

Both Oregon and South Dakota are two of the states of the United States and are located in the same latitude. It is observed that the average temperature of Oregon is comprised of relatively warmer winter, and summers are cooler in comparison to South Dakota. It is because of the proximity to the Pacific ocean, which helps in regulating the moderate type of temperature in coastal Oregon. The Pacific ocean carries the moisture containing air towards the coastal states including Oregon and maintains a moderate temperature during the winter season. In summers, there occurs dry wind but due to the presence of the Pacific ocean.