Why do the eastern slopes of the Sierra Madre Oriental receive more rain than some Pacific-facing slopes?

The eastern slopes of the Sierra Madre Oriental receive more precipitation than many Pacific-facing slopes primarily due to the effects of orographic precipitation.

As moist air masses from the Gulf of Mexico move inland, the mountains act as a physical barrier that forces the air to rise. As this air ascends, it cools and condenses, resulting in significant cloud formation and rainfall on the windward, eastern slopes.12

In contrast, areas on the leeward side of mountain ranges—such as parts of the Pacific slope—often experience a rain shadow. As the air descends on the lee side, it warms and its capacity to retain moisture increases, leading to lower levels of cloud cover and precipitation. This process explains the sharp contrast between the abundant rainfall on the eastern front of the Sierra Madre Oriental and the significantly drier conditions found in the rain shadows of other mountainous regions in Mexico.12