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.”
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Jason Box
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Zack Labe
