As the nation's climate warmed over the last 30 years, most of the West got drier and most of the East got rainier

Change in annual average precipitation, in inches, over the past 30 years compared to 20th century overall
(New York Times map; click on the image to enlarge it)

Over the past three decades, the U.S. has seen increasingly extreme weather. In the East, that tends to come in the form of flooding and storms; in the West, droughts and wildfires. 

"The map above, created using data from the National Oceanic and Atmospheric Administration, shows the eastern half of the country has gotten more rain, on average, over the last 30 years than it did during the 20th century, while precipitation has decreased in the West," Aatish Bhatia and Nadja Popovich report for The New York Times. "Thirty-year averages are often used by scientists to glean big-picture climate trends from temperature and precipitation data that varies substantially year to year."

"It’s not yet clear whether these changes in precipitation are a permanent feature of our warming climate, or whether they reflect long-term weather variability," the Times reports. "But they are largely consistent with predictions from climate models, which expect to see more precipitation overall as the world warms, with big regional differences. Broadly: Wet places get wetter and dry places get drier."

That shows on the map. The boundary between drier and wetter in the Southern Great Plains lies roughly along the 100th meridian of longitude, the traditional boundary between dry-land farming and more typical agriculture.