A tornado is a rapidly rotating vortex or funnel of air extending groundward from a cumulonimbus cloud. Tornadoes have been known to lift and move huge objects, destroy and move whole buildings long distances, and siphon large volumes from bodies of water.
Tornadoes occur in spring when warm, moist air collides with cold air resulting in winds rotating at very high speeds in a counter clockwise direction. Approximately 1,000 tornadoes are spawned by thunderstorms each year nationwide.
Tornado events are rare in Oregon. Between 1950 and 1995, there were 50 tornadoes recorded, most rated F0 (light damage) or F1 (moderate damage) on the Fujita scale. The Fujita scale assigns numerical values based on wind speeds and categorizes tornadoes from 0 to 5.
There is no record of death or injury due to a tornado in Oregon.
Take cover immediately.
Move to an interior room on the lowest floor of a sturdy building.
If in a mobile home, a vehicle or outdoors, move to the closest substantial shelter and protect yourself from flying debris.
Tornadoes can basically strike anywhere. However they tend to follow the path of least resistance. People living in valleys, which normally are the most highly developed areas, have the greatest exposure.
Big tornadoes can lift and move very heavy objects for a long distance. Tornadoes can generate a tremendous amount of debris, which can become airborne shrapnel causing additional damage. Tornadoes are almost always accompanied by heavy precipitations.
Other hazards that accompany weather systems that produce tornadoes include rainstorms, windstorms, large hail, and lightning.
The National Weather Service evaluates each major tornado to determine the accuracy of its predictions and identifications based on weather data obtained from radar and other sources, local tornado spotters, emergency operations personnel, law enforcement agencies, and the general public. The NWS goal is to improve its ability to warn affected populations.
Sources: Oregon Office of Emergency Management, National Weather Service