The reason why Maryland and the other coastal region shave milder climate is because they are heavily influenced by the sea. The water is cooling off slower and heating up slower than the land, which brings in a much more stable climate throughout the year, with milder summers and winters, where the temperatures will not go to extremely high or low numbers.
The places like Kansas and Iowa, on the other hand, are deep into the mainland. The mountain ranges stop the influence of the sea to reach them, so they are influenced by the air masses that form over the land masses, thus continental influences. The land is heating up very quickly, and also is cooling off very quickly. That leads to extreme temperatures in both the summer and the winter, with the summers being dry and hot, and the winters extremely cold and with heavy snowfall.
