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 and flash flooding.  As the upper low brought colder air. late season heavy snow ended the episode in the Blue Mountains.  Snowfall amounts in inches included Milkshakes Snotel (9) and High Ridge Snotel (7).

Hail in UMATILLA, OREGON
From 14-MAY-11 16:40:00 to 14-MAY-11 16:40:00 (PST-8)
Location: LONOLEY
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Quarter sized hail was accompanied by heavy rainfall.

Lightning in UMATILLA, OREGON
From 14-MAY-11 16:57:00 to 14-MAY-11 16:57:00 (PST-8)
Location: PENDLETON
Property damage: 0.50K
Crop damage: 0.00K
Reported by: Newspaper

Lightning struck the attic of a residence and blew out the power and sent sheetrock flying off the walls downstairs. The lightning also struck a bathroom vent on the neighbor's house.

Hail in MORROW, OREGON
From 14-MAY-11 15:15:00 to 14-MAY-11 15:15:00 (PST-8)
Location: LENA
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Flood in WHEELER, OREGON
From 15-MAY-11 05:00:00 to 18-MAY-11 23:00:00 (PST-8)
Location: SPRAY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The John Day River near Service Creek crested at 15.2 on May 17th, which was 3.7 feet above flood stage.

Heavy Snow in NORTHERN BLUE MOUNTAINS, OREGON
From 15-MAY-11 23:00:00 to 16-MAY-11 06:00:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: SNOTEL

Flood in GRANT, OREGON
From 15-MAY-11 04:30:00 to 16-MAY-11 13:30:00 (PST-8)
Location: CANYON CITY
Flood cause: Heavy Rain / Snow Melt
Property damage: 688.00K
Crop damage: 0.00K
Reported by: Newspaper

Low lying areas of Canyon City, John Day, Prairie City, and Mount Vernon were flooded along with other areas along the John Day River to the Picture Gorge area. The basement of the high school in Canyon City was flooded as were several businesses.

Flood in GRANT, OREGON
From 15-MAY-11 08:00:00 to 15-MAY-11 17:00:00 (PST-8)
Location: MONUMENT ARPT
Flood cause: Heavy Rain / Snow Melt
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Newspaper

The North Fork of the John Day River at Monument crested at 15.8 feet which was 1.8 feet above flood stage.  Flooding was also observed in Kimberly.

Flash Flood in MORROW, OREGON
From 14-MAY-11 14:00:00 to 14-MAY-11 18:30:00 (PST-8)
Location: HEPPNER
Flood cause: Heavy Rain
Property damage: 94.00K
Crop damage: 0.00K
Reported by: Emergency Manager

One to two inches of rainfall within 1 hour caused flash flooding in the Heppner and Lexington areas.  Roads were inundated. A home, two basements, and a garage were flooded.  Sandbags were used to protect homes and businesses.

Flood in UNION, OREGON
From 15-MAY-11 22:15:00 to 17-MAY-11 11:00:00 (PST-8)
Location: PERRY
Flood cause: Heavy Rain / Snow Melt
Property damage: 2.00M
Crop damage: 0.00K
Reported by: NWS Storm Survey

Heavy rainfall on above average snow pack produced record flood stage of 7.7 feet on the Grande Ronde River at Perry.  Additional flooding occurred on Little Creek, Wolf Creek, Ladd Creek, and Catherine Creek. Flooding impacted 12 thousand acres of crops and dozens of homes and businesses.  Twenty-county roads and state roads were covered including Highway 204 west of LaGrande.  Flooding also occurred at Hilgard and Red Bridge State Parks west of LaGrande.