Applied Atmospheric Dynamics
  Amanda H. Lynch and John J. Cassano

 Images

 Storm of 2003

 Projects

Projects: Tornado!

The tornado outbreak of May 2003 was a record setting one in the United States. From May 3-11, 361 tornadoes were reported in 26 states with 41 reported fatalities, 642 injuries, and over $800 million in property damage. In Missouri on May 4, several tornadoes struck, hitting the towns of Stockton and Pierce City particularly hard, with 19 reported fatalities and massive damage to their downtown business districts. The Oklahoma City area was also hard hit, including an F4 tornado which struck on May 8 in the southern Oklahoma City metropolitan area. The city of Moore, Oklahoma reported 300 homes destroyed and 1500 damaged. The next day, a single supercell thunderstorm produced ten tornadoes in central Oklahoma, including an F3 which struck in the northern Oklahoma City metropolitan area.

Tornadoes can also be associated with landfalling hurricanes. In September 2004, Hurricane Ivan spawned 117 tornadoes over a 3 day period in the United States, causing 8 deaths and 17 injuries. On September 15, an F2 tornado struck near Panama City Beach, FL which caused 1 death and 7 injuries. Also on that date, another F2 tornado struck near Bountstown, FL, resulting in 4 deaths and 1 injury.

Project Objective

Definitions

Fujita scale: A six-point scale which relates structural and/or vegetative damage to tornado intensity.

Hurricane: A tropical storm becomes a hurricane when sustained wind speeds exceed 64 knots. A pronounced rotation develops around the central core as spiral rain bands rotate around the eye of the storm. Also known as a tropical cyclone or a typhoon.

Lifted Condensation Level (LCL): The level in the atmosphere that a rising parcel lifted dry adiabatically becomes saturated.

Level of free convection (LFC): The level in the atmosphere at which a parcel rising dry adiabatically, then moist adiabatically when saturated, becomes warmer than the environment.

Equilibrium Level (EL): The level in the atmosphere at which the temperature of a buoyantly rising air parcel is equal to the environmental temperature.

Lifted Index (LI): L = (T500 - TP500) where T500 is the temperature of the environmental sounding at 500 hPa and Tp500 is the temperature of an air parcel which was lifted dry adiabatically to the LCL, then moist-adiabatically to 500 hPa. Typically the index is calculated based on the sounding taken later in the day rather than the early morning sounding in order to take into account afternoon heating. Positive LI numbers mean no significant thunderstorm or severe potential. Negative LI numbers are associated with thunderstorm potential, with LI numbers less than -4 mean severe thunderstorms are probable and tornadoes are possible.

Convective Available Potential Energy (CAPE): where ZEL is the height of the equilibrium level and Z LFC is the height of the level of free convection. CAPE is the maximum energy available to a rising parcel of air. This is the positive area on a thermodynamic diagram (where the parcel is warmer than the environment) between the level of free convection and the equilibrium level.

Vertical wind shear: The variation of wind speed or direction between different layers of the atmosphere.

Bulk Richardson Number (BRN): A dimensionless number which is the ratio of buoyant energy (CAPE) to the vertical shear of the horizontal winds. BRNs less than 10 mean thunderstorms unlikely, between 10 and 50 are associated with supercell thunderstorm development, and above 50 mean potential multicell thunderstorm development.

Individual Activity

Some suggested investigations

Describe the structure and life cycle of a supercell thunderstorm. On May 9th, 2003, a supercell thunderstorm produced 10 tornadoes in central Oklahoma. Describe the surface observations before, during, and after the event. Were the observations what you expected? Why or why not?

The CAPE, LI, shear profile, and bulk Richardson number can be used to describe the environment and tell us if the environment is conducive to tornado development. From these indices, we can estimate how much energy is available for tornadoes and whether or not tornadoes are likely to form. Estimate these indices using the atmospheric soundings from Norman, Oklahoma and Tallahassee, Florida [for the May, 2003 and Hurricane Ivan tornado outbreaks respectively].

Data

Use the links below to view data and images from this storm. All images below courtesy of the Storm Prediction Center.

 Upper air Plots

 Soundings

 Radar

 Find out about radar

• The National Weather Service office in Norman, Oklahoma
• National Hurricane Center
• Storm report on Hurricane Ivan at the National Hurricane Center
• Advisory and graphics archive on Hurricane Ivan at the National Hurricane Center
• Archive at the Storm Prediction Center
• Plymouth State Weather Center

Bibliography

 Toolbox 

•  Computer tips 
•  Weather data tips 
•  Blank maps 
•  List of Symbols 
•  Units and constants 
•  Credits 

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