When you think of weather in the western United States you probably think of high heat and little to no rain. You’d be correct, the weather patterns in that region vary significantly from the rest of the United States. But, which states have the least amount of rainfall each year?
Here are the states that rain the least:
- South Dakota
- New Mexico
These states receive less than 20 inches of rain or snow each year making them the driest regions in the United States. Keep reading to find out about what happens with the weather that makes these states receive the least rain.
What Is the United States Average Annual Precipitation?
To understand why these states receive so little rain we must look at weather patterns throughout the entire country.
The United States’ precipitation average is about 30 annually. Precipitation includes rain and snow data that has been collected independently by each state since the early 1970s. Nevada ranks as the driest state in the US while Hawaii tops the chart at an average of 63” a year.
What States Rain the Least?
Now that you know how much rain the United States usually gets, we can get into the specifics on rainfall in the driest states. Keep reading to find out more.
Nevada’s overall average is about 10” of rain annually. However, the northern parts of the state can receive around 12” and the southern parts only about 7”.
South Dakota sees an annual average of around 30” with the northernmost parts seeing as much as 28” and the southern parts only about 16”
Arizona falls on a completely different scale than what we have seen so far averaging 13” per year. This is because the mountainous regions receive most if not all of the state’s rain. The deserts of Arizona can go all year without seeing a single inch.
New Mexico’s average comes around 14” of rain similar to that of Nevada. The mountains of this state can receive as much as 20” of rain annually with the desert only seeing about 10”.
Utah can expect an average of about 11” a year. The regions of Utah however, vary greatly on the amounts of rain they will see. Some parts like the Great Salt Lake Desert can see around 8” while other parts like the mountains can see almost 50”! Despite a large amount of rain the mountains of Utah can see, it still finds itself on our list of the driest states.
Montana sees an average of 15” of rain a year. The mountainous parts of this state can see nearly 34” a year while areas in the valleys will only see about 11” a year.
Oregon is a very special state on this list. It varies so greatly, more than in Arizona. The dry plateau regions of Oregon receive as little as 8” annually which is why it falls on our list of dry states. However, the coastal regions can receive anywhere from 60 – 200” per year which is over the national average.
Wyoming averages about 12” of rainfall annually. The maximum average is around 32” and the minimum average is 5”.
Colorado sees an average of 17” of rain each year. Places like Alamosa get only about 9” of rainfall, meanwhile Aspen can receive anywhere up to 25” annually.
Idaho’s average comes in at 18” a year. Ranging from 12” in the low elevations in the southern part of the state to 35” in the mountainous northern areas. Since more of Idaho sees the lower numbers it earns its name as one of the dry states.
Why Do Some States Rain Less?
It may seem concerning to some that some states rain less than others. While you may think that this is the result of global warming, there are some other factors in play as well. Let’s go over them below.
The Rain Shadow
One of the biggest reasons the western United States is so dry is because of “ the rain shadow.”
The rain shadow is where the rain gets blocked off by the Rocky Mountains and is unable to make it over the mountain range to these dry states.
The mountains also keep the Pacific ocean moisture from creating that humid air that most of the United States are used to. Warm air ascends into the mountains to form clouds but dries out before it ever reaches the other side.
Landlocked by Mexico
Another reason for the lack of moisture in the western United States is Mexico.
This Country keeps moisture from reaching the southernmost portions of the United States. The Westerlies push warm humid air up and into the West side of Mexico where it dries out before ever making it to the United States.
The Trade Winds push into the East side of Mexico doing the same thing with humid air never reaching the United States.
In conclusion, the western United States holds a large portion of the driest states in our country because of weather phenomena and land-locked regions that make it almost impossible for moisture and rain to reach these drought-prone areas.