It’s been a hot summer in Washington, but it’s a dry heat. Literally.
The state is experiencing its driest summer since at least 1900, with local rain amounts from 70 percent to 85 percent below normal.
The lack of moisture from June 1 through Aug. 31 set records in the Puget Sound region and the Cascade Range. But the usually arid sections of eastern Washington were even more parched than usual, said state climatologist Philip Mote, a research scientist with the Pacific Northwest Climate Impacts Group at the University of Washington.
“There were parts of eastern Washington that got no rain at all in July, and several cities in that part of the state that got just tiny amounts,” Mote said.
Rainfall in western Washington and the Cascades averaged 30 percent to 33 percent of normal for the three months, he said, while eastern Washington’s totals were just 15 percent to 25 percent of normal.
Mote used figures from the National Climate Data Center that show precipitation averages for various regions of the state, then employ those regional averages to determine a statewide average. He compared the data center figures with numbers from the Historical Climate Network, which uses the most reliable readings from each region to establish averages dating back more than a century.
National Climate Data Center figures put the statewide average precipitation at 1.12 inches for the three months, compared with a normal of 3.87 inches, while the Historical Climate Network numbers place the average at 1.09 inches, compared with an average of 4.05 inches.
The numbers indicate this summer is the state’s driest since at least 1900, and possibly since record keeping began in 1895, Mote said, though the numbers from 1895 are too sketchy to determine whether that summer might have been drier than this summer. The second-driest summer was in 1919 and the third was in 1967.
Arid conditions have worsened fire danger statewide. State Department of Natural Resources measurements place the moisture content of dead wood that could fuel forest fires at 20 percent to 30 percent below normal across eastern Washington, said Greg Sinnett, the department’s chief meteorologist. The moisture content was 15 percent to 20 percent less than normal west of the Cascades, and was down 5 percent to 10 percent in coastal areas.
In some parts of eastern Washington, moisture levels early in the summer were the lowest ever recorded for the dates the measurements were taken, and those records have persisted throughout the summer, Sinnett said. Concerns about fire mount whenever there are two consecutive dry months between June and October, he said, and those concerns rose quickly this year when moderate June rains, which often delay the onset of fires, didn’t materialize.
“We knew from the start of the season that things were going to be a concern, and unfortunately they didn’t improve,” he said.
It will take some persistent precipitation to alleviate the fire conditions, he said, especially high in the evergreen forests where needles are withering for lack of moisture.
“We really need to see the soil and the canopy recharged with water, and that will take four or five storms with good rainfall and strong wind so the water can really penetrate,” Sinnett said.
This summer’s dry conditions weren’t affected by the El Ni?limate phenomenon that had mild impacts on Northwest weather last winter and spring but had dissipated before the summer dry spell, Mote said. He said there is no particular reason for the prolonged shortage of moisture.
“It was just a dry summer,” he said. “As we look at the records over the last hundred years, while it stands out as a dry year, it certainly doesn’t stand out as a trend that this is the way things are going. There’s nothing to indicate the trend is either up or down in terms of summer precipitation.”
For more information, contact Mote at (206) 616-5346 or http://www.climate.washington.edu