An upper level low pressure system moved over the Pacific Northwest. Moist and unstable conditions ahead of the low triggered widespread thunderstorms with heavy rainfall and isolated large hail. This combined with the abundant spring snow-pack and wet ground to cause flooding. A 75 yard wide mudslide closed Highway 410 at milepost 87. As the upper low brought colder air. late season heavy snow ended the episode in the Blue Mountains.  Snowfall amounts in inches included Touchet Snotel (7).

Thunderstorm Wind in WALLA WALLA, WASHINGTON
From 14-MAY-11 17:20:00 to 14-MAY-11 17:20:00 (PST-8)
Location: VILLARD JCT
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Microburst like wind gust blew trampoline over and kicked up several pieces of debris.  Several tree limbs 1 to 3 inches in diameter have fallen.

Thunderstorm Wind in BENTON, WASHINGTON
From 14-MAY-11 17:50:00 to 14-MAY-11 17:50:00 (PST-8)
Location: (RLD)RICHLAND ARPT
Magnitude: 51.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Flood in BENTON, WASHINGTON
From 17-MAY-11 05:00:00 to 19-MAY-11 13:00:00 (PST-8)
Location: PROSSER
Flood cause: Heavy Rain / Snow Melt
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The Yakima River at Kiona crested at 15.5 feet on May 18th, which was 2.5 feet above flood stage.  The flooding damaged several businesses in Prosser and farmland, roads, businesses, and residential areas from Prosser to Richland, including the Beach RV Park in Benton City and the West Richland Golf Course.

Flood in YAKIMA, WASHINGTON
From 15-MAY-11 03:45:00 to 23-MAY-11 12:15:00 (PST-8)
Location: CLIFFDELL
Flood cause: Heavy Rain / Snow Melt
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Newspaper

Flooding closed sections of Highway 410 and other roads along the Naches River from Cliffdell to Yakima. High water and large debris damaged bridges. The Naches River crested at 20.4 on May 15th, which was 3.4 feet above flood stage.  At Cliffdell, the river crested at 32.2 feet on May 15th, which was 1.3 feet above normal.

Flood in YAKIMA, WASHINGTON
From 15-MAY-11 16:30:00 to 17-MAY-11 15:30:00 (PST-8)
Location: POMONA
Flood cause: Heavy Rain / Snow Melt
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The Yakima River at Umtanum crested at 36.5 feet on May 16th, which was 1 foot above flood stage.  At Parker the crest was 13.2 feet on May 16th, which was 3.2 feet above flood stage.  Reported rainfall amounts on May 14-15 were between 3 and 4 inches.

Flood in KITTITAS, WASHINGTON
From 15-MAY-11 00:00:00 to 16-MAY-11 23:00:00 (PST-8)
Location: LIBERTY
Flood cause: Heavy Rain
Property damage: 4.00M
Crop damage: 0.00K
Reported by: Newspaper

Flood waters damaged or closed 22 roads along Manastash, Taneum, Cooke, Coleman, Wilson, and Caribou Creeks.  Bridges and irrigation systems were also impacted.

Lightning in KITTITAS, WASHINGTON
From 14-MAY-11 00:00:00 to 14-MAY-11 00:00:00 (PST-8)
Location: (ELN)BOWERS FLD ELLE
Property damage: 300.00K
Crop damage: 0.00K
Reported by: Newspaper

Lightning started a roof fire which damaged a few other rooms of a residence.

Debris Flow in EAST SLOPES OF THE WASHINGTON CASCADES, WASHINGTON
From 15-MAY-11 08:30:00 to 15-MAY-11 08:30:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways