Oklahoma City Tornado May 3, 1999

(Last updated May 12, 2002)

A series of tornadic thunderstorms wreaked havoc from central Texas to southern Kansas on May 3-4, 1999. Over fifty tornadoes occurred, with central Oklahoma the worst hit area. This page shows several images from the Twin Lakes, OK, radar of the the tornadic storm that moved through the Oklahoma City area.


(77K GIF)	(71K GIF)

The first image (77K GIF) is a reflectivity image at 6:31 PM CDT. Radar reflectivity is a measure of how much of a radar pulse bounces off a target and returns to the radar. For weather radar, the heavier the rain and hail, the greater the signal returned to the radar and the hight the reflectivity. This images shows the tornadic thunderstorm about the time the Oklahoma City/Moore tornado first touched down. Notice the large area of yellow, orange, and red in the center of the picture, and how these colors curve around an area of green just north of the town of Amber. These are the areas of heavy rain and hail (higher reflectivity), forming a hook echo around the lighter precipitation (lower reflectivity) just north of Amber. This is a pattern characteristic of a supercell thunderstorm. The area of lighter precipitation is caused by the thunderstorm's updraft, which is so strong that little precipitation can fall through it.

The second image (71K GIF) is a storm-relative velocity image of the cell. The National Weather Service's doppler radars can seen the wind blowing toward (green colors) or away (red colors) from the radar site. In a storm-relative velocity image, the motion of the storm has been subtracted from the winds, making it easier to see any rotation in the storm. Notice the couplet of bright green and bright red and pink near Amber. This is the strong cyclonic circulation associated with the developing tornado.


(91K GIF)	(73K GIF)

The reflectivity image (91K GIF) on the left shows the storm at 6:56 PM. The hook echo has become even more pronounced just west of Lancaster, with the blue colors in the hook showing even lighter precipitation than before. The storm-relative velocity image (71K GIF) on the right shows winds greater than 75 mph blowing toward the radar (bright green) right next to greater than 75 mph blowing away from the radar (pink). This sharp change in the winds is a Tornado Vortex Signature, the signal that appears when a tornado is large enough or strong enough to be directly detected.

The tornado track map created by the National Weather Service Forecast Office in Norman, OK shows the tornado reached F5 (maximum intensity) on the Fujita tornado scale around this time. Eyewitness accounts indicate the tornado was about a mile wide.


(86K GIF)	(79K GIF)

The reflectivity image (86K GIF) on the left shows the storm at 7:32 PM PM. Notice the increased reflectivity (the white pixels) at the end of the hook. The increase is mostly likely due to the radar detecting the debris raised by the tornado as it moved through the Oklahoma City metropolitan area. The storm-relative velocity image (79K GIF) continues to show the well-defined velocity couplet associated with the tornado, which has been on the ground for an hour.

These images are used with the kind permission of National Weather Service Forecast Office in Norman, OK and can be found in the May 3 tornado outbreak section of their web site. Another National Weather Service office with information on the outbreak is Tulsa, OK.

There are numerous other on-line sources of information on this notorious event. Satellite imagery can be found at:

Other information is available from the National Severe Storms Laboratory, the Doppler on Wheels web site, and the Oklahoma Climate Survey. Last, but certainly not least, pictures and chase accounts of the May 3 tornadoes are available from Roger Edwards and Jim Leonard.

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