As rest of U.S. baked, Northwest sat under damp blanket of clouds
A hot July also contributed to the warmest 12-month period ever recorded in the U.S., statistics showed.
The New York Times
It may come as little surprise to the nation's corn farmers or resort operators, but the official statistics are in: July was the hottest month in the Lower 48 states since the government began keeping temperature records in 1895.
The average temperature last month was 77.6 degrees — 3.3 degrees above the average 20th-century temperature, the National Oceanic and Atmospheric Administration reported Wednesday. July thereby dethroned the record of 77.4 degrees set in July 1936, the agency said.
Warmer-than-average temperatures gripped much of the country last month, with the biggest departures from the 20th-century average reported across most of the Plains, in the Midwest and along the Eastern Seaboard, the agency's report said. Virginia had its warmest July on record, with the average temperature 4 degrees above the norm, it added.
But as the rest of the country baked, much of the West Coast sat under a cool, damp blanket of clouds, and July's mean temperature in the Seattle-Tacoma area was 64.3 degrees. While gray skies are a byproduct of living close to the sea, University of Washington meteorologist Cliff Mass explained that our cloudy layer could become more pronounced as the globe warms.
"Our simulations show we could have more of these low clouds in the spring and summer," he said.
A hot July also contributed to the warmest 12-month period ever recorded in the U.S., the statistics showed.
NOAA climatologists noted that by the end of the month, about 63 percent of the nation was experiencing drought conditions, which contributed to the high temperatures.
"July was a pretty interesting month because there were two different things at play," Jake Crouch, a climatologist at the agency's National Climatic Data Center in Asheville, N.C., said in an interview. "We saw very warm daytime temperatures over a large part of the country related to the ongoing drought, just as in 1936. When soils are dry, especially during the summer, it drives the daytime temperatures up. But this is a very local effect.
"On the other side, at the national level, we have also seen very warm nighttime temperatures, and that is part of a long-term trend we've seen across the contiguous U.S. over the past several decades. The hotter days increase the amount of moisture the lower atmosphere can hold, and this means it doesn't cool off as much at night anymore."
"This clearly shows a longer-term warming trend in the U.S., not just one really hot month," Crouch said.
Asked whether the July heat record was linked to rising atmospheric concentrations of greenhouse gases, Crouch said, he could not draw that conclusion.
But the new records are certain to contribute to the debate over whether some of the recent weather extremes in the U.S. and elsewhere, from tropical storms to droughts, can be directly attributed to human-induced global warming.
A prominent NASA scientist, James Hansen, reported in a journal article published Monday that recent extremes of hot weather have been so pronounced that scientists can say with near-certainty that events like the Russian heat wave of 2010 or the Texas heat wave of 2011 would not have happened unless global warming was under way.
While some scientists praised his results, others argued that the evidence was still insufficient for attributing a specific heat wave or storm to climate change.
A vast majority of scientists agree that such events will become ever more common as the planet warms, however.
In the U.S., the only hope for substantial relief from warmer-than-average temperatures in the coming weeks and months would be a striking atmospheric change, like the development this autumn of the weather pattern known as El Niño or a tropical cyclone that moves into the central part of the country from the Gulf of Mexico, scientists said Wednesday.
Last week, more than half of all U.S. counties — 1,584 in 32 states — were listed by the U.S. Department of Agriculture as primary disaster areas this growing season, the vast majority of them mired in the worst drought in decades.
Additional information from Seattle Times archives and the National Weather Service is included in this report.