The climate of the United States features a wide array of weather patterns, from the humid subtropics of the southeast to the temperate rainforests of the Pacific Northwest. Precipitation, which includes all forms of water released from the atmosphere, such as rain, snow, sleet, and hail, varies dramatically across the country. Understanding which regions receive the least amount of moisture requires looking at long-term averages. These averages highlight the vast climatic differences between states, which result from large-scale atmospheric circulation and significant geographical features.
Identifying the Driest State
The state that consistently receives the least amount of precipitation annually is Nevada. Based on long-term climate data, the statewide average for total yearly precipitation is approximately 9.5 inches. This figure places Nevada far below the national average for the contiguous United States, which is roughly 30.21 inches per year. Nevada’s climate is predominantly arid and semi-arid, possessing 22 of the Top 25 driest years recorded for any state in the US.
How Precipitation is Measured
Official precipitation figures are calculated by federal agencies like the National Oceanic and Atmospheric Administration (NOAA) using standardized methods. Precipitation encompasses the liquid equivalent of all forms of atmospheric water, meaning the melted volume of snow, sleet, and hail is included in the total. Sophisticated instruments, such as weighing precipitation gauges, are used to collect and measure the depth of water with high accuracy.
These gauges often employ multiple sensors to record the depth of the collected water at frequent intervals. The data points are then processed to establish reliable long-term annual averages, typically calculated over 30-year periods known as Climate Normals.
Geographical Causes of Aridity
The primary reason for Nevada’s dryness is the meteorological phenomenon known as the rain shadow effect. The state lies almost entirely in the Great Basin, situated to the east of the towering Sierra Nevada mountain range. Prevailing winds carry moist air masses eastward from the Pacific Ocean toward the continent.
As this moisture-laden air encounters the steep western slopes of the Sierra Nevada, it is forced to rise quickly, a process called orographic lifting. The rapid ascent causes the air to cool, leading to condensation and the release of nearly all its moisture as rain or heavy snow on the mountains’ western side. By the time the air descends on the leeward (eastern) side into Nevada, it has been stripped of its water content, creating the arid conditions characteristic of the Great Basin desert.
The Driest Specific Locations
While Nevada is the driest state overall, certain locations within the region experience even more extreme aridity. Indian Springs, in northwestern Nevada, records one of the lowest precipitation totals in the entire state, averaging a mere 2.91 inches annually. Major population centers also reflect the regional dryness, with Las Vegas averaging only about 4.2 inches per year. Neighboring states also contain pockets of extreme dryness. For instance, Yuma, Arizona, receives an annual average of less than five inches, and Death Valley, California, is one of the driest places on the planet, underscoring the severity of the rain shadow.