The U.S. just had its warmest May in history, blowing past 1934 Dust Bowl record
7 June, 2018
Almost every tract of land in the contiguous United States was warmer than normal in May, helping to break a Dust Bowl-era record.
The month’s average temperature 0f 65.4 degrees swept by the previous high mark of 64.7 degrees set in 1934. Temperatures were more than 5 degrees above normal, according to the National Oceanic and Atmospheric Administration, which published a May U.S. climate assessment Wednesday.
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.
The National Weather issued a flash flood emergency for Ellicott City, Md., on May 27, after 3-6 inches of rain fell in just two hours. (JM Rieger, Taylor Turner, David Bruns/The Washington Post)
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.
[In the Northeast, just a few hundred miles separate record wet and dry]
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.
(NOAA, adapted by Capital Weather Gang)
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.
The average temperature over the Lower 48 states in May, 1895-2018. (NOAA)
The toasty pattern presented a massive contrast from April, which ranked the 13th-coldest on record, more than 2 degrees below average.
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.
[Weather whiplash: Midwest catapults from coldest April to hottest May on record; Minneapolis notches earliest 100.]
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.
The nation just witnessed its warmest May on record, but, it turns out, that month was only one small piece of a much longer and historically unprecedented stretch of warmth.
Data from the National Oceanic and Atmospheric Administration indicate that the past 36-, 48-, and 60-month periods rank warmest on record for the Lower 48, in records that date to 1895.
Because weather patterns vary somewhat at random, not every month during this unrivaled warm era set a record for warmth. April even ranked as the 12th-coldest on record as the jet stream plunged south for much of the month. But that brief, cool excursion was more than offset by the record-warm May.
More often than not, months have been warmer than normal if not record-challenging. Averaging them, the warmth of the recent 3-, 4-, and 5-year periods has no match.
Average temperature ranking for the Lower 48 states over the past 48 months. Dark red indicates warmest on record. Orange indicates much warmer than normal. (NOAA)
This collection of months is a reflection of long-term climate warming, set in motion by rising concentrations of greenhouse gases in the atmosphere.
The four warmest years on record (2015, 2017, 2016 and 2012) have occurred since 2012, and eight of the 10 warmest years have happened since 1998. Our nation has warmed at a rate of between 0.3 to 0.4 degrees per decade since the 1980s.
[Climate change in the United States presented in 123 red, white and blue stripes]
We should expect future groups of months and years to set more records. “The annual average temperature of the contiguous United States is projected to rise throughout the century,” says the Climate Science Special Report of the federal government’s Fourth National Climate Assessment.
The average temperature for the period 2021 to 2050 is predicted to be between 2.5 and 2.9 degrees warmer than the period from 1976 to 2005. “Notably, a 2.5°F (1.4°C) increase makes the near-term average comparable to the hottest year in the historical record (2012),” the report said. “In other words, recent record-breaking years may be ‘common’ in the next few decades.”