Tornadoes

Water spout

A tornado over water (L Pressure)

Average times for Tornadoes

Afternoon - Evening (3:00-7:00)

Average Months for Tornadoes

April, May, June, July

Ideal Conditions For the Shear Produces Tornadoes

Cool, dry high altitude winds Warm, moist surface winds from the Gulf of Mexico

Tornado Development

Generally Tornadoes form when there is shear in wind directions caused by winds at high altitudes approaching from one direction and winds at low altitudes approaching from another direction creating a "roll" of horizontal currents as warm, moist air rises over an advancing cold front This horizontal roll becomes vertical by strong updrafts producing a wall cloud Funnel clouds, strongly rotating winds in a vortex, form within and descend from the slowly rotating wall cloud, and when they approach or touch the ground they form a tornado.

Tornado Warning

Issued when Doppler radar shows an indication of rotation and the formation of a vortex OR if a tornado has been sighted

Tornado Watch

Issued when thunderstorms appear capable of producing tornadoes based upon radar images

Tornado Preparedness and Safety

Move to a tornado shelter (storm cellar), basement, or interior room without windows The safest place is the side or corner of an underground room opposite the tornado's direction of approach (usually the northeast corner), or the central-most room on the lowest floor. Taking shelter under a sturdy table or under a staircase increases chances of survival even more Restrooms in commercial buildings are excellent shelters If in a car or on a motorcycle or bicycle . . . PARK IT . . . and get into a ditch Flying debris is extremely dangerous, so cover your head Highway overpasses are extremely bad shelters since they serve as wind tunnels

Total Wind Speed

The total wind speed of a tornado is greater on one side than on the other. When facing an onrushing tornado, the strongest winds will be on your left side.

Tornadoes

Tornadoes are funnel shaped clouds in low pressure cells associated with large thunderstorms and some hurricanes and snow storms They are natures most violent storms and the most significant natural hazard in the mid-west of the US; more occur in the US than anywhere else on earth Wind velocities can be over 300 mph Diameters range from a few meters up to 1.5 km Paths are relatively short (<30 km long), but they can skip and form discontinuous paths 100's of km in length Time on the ground is variable, but generally short and rarely exceeds 30 minutes

Super-Cell Thunderstorm Development

Tornadoes are most likely to form in a conditionally unstable atmosphere where there is strong vertical wind shear for supercell thunderstorm development. Here, wind speeds increase with height and winds change direction with height, usually from more southerly at the surface to more westerly at higher levels.

More About Tornadoes

Tornadoes generally form at the trailing edfe of a severe thunderstorm; therefore mnay are preceded by wind and rain, then hail, then a "calm", then the tornado. this catches people off guard, unless they have been warned by authorities Tornadoes are preceded by a hissing sound that turns into a roar. Many people describe the sound as that of an oncoming freight train

Wind Shear

Wind shear produces a spinning vortex tube that gets pulled into the thunderstorm by low pressure updrafts and tornadoes are generated that may touch the ground

Tornado is Born

a.) A spinning vortex tube created by wind shear b.) The strong updraft in the developing thunderstorm carries the cortex tube into the thunderstorm producing a rotating air column that is oriented in the vertical plane