Second warmest spring ends with warmest May since 1993

agweathernet-logo-250PROSSER, Wash. – Spring 2015 was the state’s warmest recorded spring since the early 1990s. The low temperatures were particularly warm in the unsettled and somewhat humid conditions of late spring. South central Washington was wetter than western areas in May – a significant departure from normal conditions.

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.”

A Web-based, publicly available system, AgWeatherNet ( provides access to near real-time weather data and value-added products from WSU’s statewide weather network, along with decision aids for agricultural producers and other users. It is based at the WSU Irrigated Agriculture Research and Extension Center in Prosser.

The non-temperature weather story was the incredible 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 in excess of one inch of rain, with isolated reports of more than 2 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.”

The rainfall was widespread in the driest part of the state. Prosser recorded 1.37 inches of rain – a daily record.

May 13 was also a very cool day, with highs in the 50s in much of south central and eastern Washington.

Earlier in spring, March was nearly five degrees above normal at Prosser and was the warmest on record. March 27 was an especially hot day, as Wapato reached a monthly record high of 80 degrees.

However, several cool storms in early April brought wind, rain and mountain snow to the region. The high was 45 degrees at Garfield East on April 14, and Ritzville fell to 23 degrees on the morning of April 15.

Overall, April was slightly warmer than normal and quite dry; Moxee experienced a precipitation-free month.


Nic Loyd, WSU AgWeatherNet meteorologist, 509-786-9357,
Gerritt Hoogenboom, WSU AgWeatherNet director, 509-786-9371,