What prevents the humid winds that strike east coast from reaching very far inland?

The Appalachian Mountains prevent the humid winds that strike the east coast from reaching very far inland. These mountains are a long and high mountain range that runs parallel to the Atlantic Ocean. They act as a barrier to the winds, causing them to rise and cool, which condenses the moisture in them. This results in heavy rainfall on the windward side of the mountains, but much less rainfall on the leeward side.