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