PROSSER, Wash. – Severe thunderstorms, torrential downpours, flash flooding, and large hail may sound like typical summer weather in the Midwest, but also aptly describes Washington’s July weather.
On the final day of a week-long stormy period, the July 20 severe weather outbreak featured the strongest and most widespread thunderstorm activity of the month. The result was hail as large as 1.75 inches in diameter, along with significant crop damage in eastern Washington. Agricultural impacts included scattered crop losses of 25 percent to 100 percent. The area north of Sunnyside was especially hard hit, and received hail as large as ping pong balls.
“The strong thunderstorms on July 20 caused significant crop damage across eastern Washington,” said AgWeatherNet director Gerrit Hoogenboom. “As is often the case with severe weather, the agricultural impacts were highly variable. Devastating losses were sustained in some areas, while other nearby areas were relatively unaffected.”
Thunderstorms were a common occurrence in the state between July 14 and 20, as upper-level low-pressure system to the south caused moist and unstable southerly flow over the region. “The active weather pattern that occurred during the third week of July was remarkable for several reasons,” said AgWeatherNet meteorologist Nic Loyd. “The July 20 severe weather outbreak featured an unusually large area of intense thunderstorms. However, it is also rare to have a prolonged period of stormy weather that persists for an entire week.”
Storms began to pummel the region as early as July 14. Pomona, north of Selah, received an all-time record rainfall (1989 to present) of 1.69 inches, including a record .56 inches in only fifteen minutes. In the Okanogan region, Malott recorded 2.3 inches of rain on July 15, including an incredible .73 inches in fifteen minutes.
The stormy period was preceded by the most significant heat wave in several years in eastern Washington. The AgWeatherNet station at Sunnyside recorded an all-time record high temperature of 104 degrees on July 8, while the Mesa Southeast station in the Columbia Basin topped 107 degrees.
The thunderstorms that moved through south-central Washington during the evening of July 8 caused an uncommon event across the region. Significant rain fell in some locations that had climbed over 100 degrees earlier in the day, making July 8 the hottest rain day ever in parts of central Washington.
Parts of central Washington recorded high temperatures in excess of 100 degrees for up to five straight days, while the AgWeatherNet station at Wahluke Slope remained above 70 degrees for seven consecutive days and nights. Overall, July temperatures were slightly above average in eastern Washington, and slightly below average in western Washington.
For more information about July weather, as well as other weather information, visit the AgWeatherNet website. The July Weather Review is located under the News link. 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.