RAMMB Satellite Case Studies

The "Killer" Tornado Oubreak in Northeast Georgia on 20 March 1998

The following data is from a special 5-minute data set being collected by the new GOES-10 satellite. It covers the period from 0830 to 1335 UTC for the infrared channel data and 1130 to 1335 UTC for the visible channel, and includes the time during which the killer tornado was on the ground. The tornado touched down 2 miles south of Murrayville, GA (about 6 miles north of Gainesville) at 6:20 AM EST and traveled 11.5 miles northeast. 11 people in Hall county, and 2 in White county Georgia were killed.

Our first, quick look suggests the following: All of the precursor action was well before dawn so visible imagery is not helpful during the period when the storm was forming and intensifying. The infrared imagery shows that the storm of interest formed just behind the major squall line, on what may be an outflow boundary. Though the size of the storm is not large, nor is the top very cold (compared to nearby storms), there is a storm-scale circulation evident in the subsidence around the anvil. There is also a possible storm split, with a left moving overshooting top heading off to the north with the synoptic flow, and a right mover moving almost due easterly.

These digital, McIDAS format data files are available by anonymous FTP to: "canopus.cira.colostate.edu". They are in directory 98079_GA_tor. The 5-channel, five-minute sector files are named with the conventional McIDAS "AREAnnnn" format, with nnnn=1700's indicating GOES Imager channel 1 (4 km), nnnn=1900's for channel 1 (1 km), nnn=3000's for channel 3, nnnn=4000's for channel 4 and nnnn=6000's for the fog product. Channel 1 is visible, channel 3 is at 6.7 micrometers (water vapor), and channel 4 is the conventional IR window.

Gator1- Gator50.gif are a series of gif images, centered over Atlanta, showing the enhanced (to highlight the cold cloud-tops) IR imagery from channel 4. These images show the environment well before the storms began, 0515 UTC, through the rest of the period defined above. An 8-frame loop from this dataset can be viewed by clicking on the "thumbnail" image below.