March through May 2015 was the state of Washington’s warmest recorded spring since the early 1990s, with low temperatures particularly warm, according to the Washington State University AgWeatherNet based in Prosser.
The Mid-Columbia and nearby areas were wetter than western areas of the state in May, a significant departure from normal conditions, it said.
At Prosser, temperature highlights from the season included: the second warmest spring on record; the warmest spring low on record; the warmest May since 1993; the warmest May low on record and the warmest March on record.
“The dominant weather pattern in May was an unusual split flow setup that featured a ridge northwest of Washington,” said AgWeatherNet meteorologist Nic Loyd. “That cut off lows to our south, so we observed warm, moist and unstable conditions.”
May also may be remembered for the rainfall on May 13 in south central Washington. Much of the lower Columbia Basin from the lower Yakima Valley and Horse Heaven Hills eastward to the Tri-Cities and Walla Walla recorded more than one inch of rain, with isolated reports of more than two inches.
“The rainfall could not have come at a more opportune time for this region, given that the Roza Irrigation District water was shut off for much of May,” said AgWeatherNet director Gerrit Hoogenboom. “Unfortunately, the one-day event will have little impact on the long-term snow drought situation.”