EF5 Tornado Moore, Oklahoma: May 20, 2013

Tornadoes

EF5 tornado crossing the Patuxent River near Solomons, MD

May 28, 2002

Basic questions about tornadoes

• What is the definition of a tornado?

• What makes tornadoes visible?

• What defines tornado intensity?

• How do tornadoes form?

• Where do they occur most often?

• Is tornado frequency increasing?

• Is there such thing as tornado safety?

Some Tornado Links:

Storm Prediction Center

Tornado History Projecthttp://www.tornadohistoryproject.com

http://www.spc.noaa.gov/wcm/

Supercell: Long-lived (greater than 1 hour) highly organized convective thunderstorm that is tilted and rotating, often generating tornadoes. Mesocyclone: Supercell detected by Doppler radar.

Tornado: Funnel-shaped concentrations of extremely rapidly rotating air (vortices), often emerging from supercells or mesocyclones, visualized by condensation & dust

Derecho: Line of fast moving supercells.

Tornado Terminology

Supercell(Mesocyclone)

Wall Cloud(tornado precursor)

Tornado Funnels* with Wall Clouds

* Funnels are made of condensed water droplets & dust

Funnel Shapes

Water Spout

Dust Sheaths

Tornadoes in Urban Environments

Tornado Behavior

• Travel speeds range from almost stationary to more than 90 km/hr. A typical tornado travels around 15-30 km/hr.

• Doppler radar measured wind speeds in a tornado - strongest was 500 km/hr measured on May 3, 1999 at Moore, Oklahoma.

• Tornado touchdown time ranges from a few seconds to several hours. The average is about five minutes.

•Most tornadoes (but not all) in the Northern Hemisphere spin counterclockwise (cyclonic vorticity).

Tornado Anatomy

Model of a Tornado: the Bathtub Vortex

Fujita Tornado Intensity Scale

• Originally (1970s) F0-F10 (F10=speed of sound in air)• Revised in 1990s; allowing more EF5s

Tetsuya Fujita

Tornado Reports, 1950-2005

Tornado Alley

Are tornadoes becoming more frequent?

Common Sense Tornado Safety

Don’tDo

Use your basement or stairwell!!

Tornado ProtectionDrill