The 1934 record was impressive, enduring for decades even as the climate has warmed because of increasing greenhouse gases in the atmosphere. One of the main reasons May 1934 was so hot was because it was so dry, posting the least precipitation for the month on record. When the land surface is dry, it heats up faster.
A combination of drought and farming practices had left fields bare of vegetation in 1934, resulting in “an estimated 35 million acres of formerly cultivated land had been rendered useless for farming,” according to History.com.
The parched conditions were so severe that on May 11 “a massive dust storm two miles high traveled 2,000 miles to the East Coast, blotting out monuments such as the Statue of Liberty and the U.S. Capitol,” History.com wrote.
In May 2018, temperatures soared to record levels even without as much help from dry soils. Precipitation was a hair above normal averaged over the nation. Maryland, hit by major floods in Frederick and Ellicott City, had its wettest May on record. So did Florida. Asheville, N.C., posted 14.68 inches of rain, its wettest month in history.
Parts of the country, including the south-central United States, New England and the Pacific Northwest, were drier than normal, but overall the percentage of the nation affected by drought fell more than 2 percent during the month.
Rather than dry soil, the record warmth this past May can be traced to the jet stream, the high-altitude current that separates cold air from warm air. It lifted north of the U.S.-Canadian border for much of the month, allowing widespread abnormally warm air to flood northward.
It’s also fair to say that rising greenhouse gas concentrations, which have pushed May temperatures higher over time and now even above those torrid Dust Bowl years, contributed to the record temperatures.
Eight states had their warmest May on record: Virginia, Arkansas, Illinois, Indiana, Kentucky, Missouri, Ohio and Oklahoma.
Across the nation, more than 8,500 warm-temperature records were set at weather stations during the month, compared with 460 cold records. On May 28, Minneapolis notched its earliest 100-degree reading on record.
Thanks to May’s record-setting warmth, the nation posted its 22nd-warmest spring (March through May) in records that date back to 1895, more than offsetting the cold April.