Questions: The humidity over the Great Basin of the Western United States is typically low due to the moisture of the Pacific Ocean getting trapped in the Sierra Mountains. This is called downslope warming and drying.

The statement provided describes a meteorological phenomenon related to the climate of the Great Basin in the Western United States. The process mentioned is known as "rain shadow effect," which is a common occurrence in regions where mountain ranges block the passage of moist air, causing one side to receive precipitation while the other side remains dry.

Here's a breakdown of the process:

1. Moisture Source: The Pacific Ocean serves as a significant source of moisture. As air masses move eastward from the ocean, they carry moisture with them.

2. Mountain Barrier: The Sierra Nevada Mountains act as a barrier to these moist air masses. As the air ascends the western slopes of the mountains, it cools and condenses, leading to precipitation on the windward side.

3. Rain Shadow Effect: Once the air crosses over the mountain peaks and descends on the leeward side (the side facing away from the wind), it warms up and dries out. This process is known as adiabatic warming, where the air pressure increases as the air descends, causing the temperature to rise and the relative humidity to decrease.

4. Resulting Climate: The Great Basin, located on the leeward side of the Sierra Nevada, experiences low humidity and arid conditions due to this rain shadow effect. The lack of moisture leads to a desert-like climate in this region.

In summary, the low humidity over the Great Basin is primarily due to the rain shadow effect caused by the Sierra Nevada Mountains, which block moist air from the Pacific Ocean, resulting in downslope warming and drying on the leeward side.