The National Weather Service (NWS) confirmed an EF-0 tornado with winds of 65 to 85 mph hit the barn about two miles northeast of Hockinson in Clark County, just after 4 p.m. PDT Thursday.
The roof of the barn was partially torn off with debris spread out in a 120-degree cone from the building with the largest objects thrown to the north northeast of the structure.
KPTV reported the barn, built in 1945, had partially collapsed shortly after being impacted by the tornado.
No trees or other structures were impacted by the tornado.
Tornadoes are fairly rare in the state of Washington.
According to the Storm Prediction Center, the state sees an average of only two tornadoes each year.
The tornadoes that do occur are typically very weak on the order of EF-0s and EF-1s on the Enhanced Fujita Scale.
Strong tornadoes need severe thunderstorms fed by large changes in temperature in the upper atmosphere. Severe thunderstorms typically need much colder air moving in aloft to make the air very unstable.
The so-called "Tornado Alley" in the Midwest is ripe for severe weather due to frequent battles between cold, arctic air marching south of out Canada colliding with very warm, moist air moving north from the Gulf of Mexico.
But in the Pacific Northwest, the cool waters off the Pacific Ocean are a great moderating force that keeps temperature changes from being too drastic, and thus tornadoes are quite rare.