Service Enhancement Project
By Alan Gerard...SOO

 

 

Synopsis

During much of May 2, 1997, and the early morning hours of May 3, 1997, a significant outbreak of severe thunderstorms occurred over the Lower Mississippi Valley. Severe thunderstorms were concentrated in the NWSFO Jackson County Warning Area (CWA), which includes northeast Louisiana, southeast Arkansas, and much of Mississippi the north quarter and the extreme south. NWSFO Jackson issued 75 short-fuse warning products (severe thunderstorm, tornado, and flash flood) and 20 statements (severe weather and special weather) during an 18 hour period starting just before Noon on May 2 and ending just before 6 am on May 3. This is an average of about 1 non-routine product issued every 11 minutes.

The likelihood that a severe weather outbreak would occur during the period was recognized by forecasters well in advance of the event. The earliest mention of the potential for severe weather, the evening of May 2 was made in the 425 am May 1 State Forecast Discussion(SFD) product. By the 420 pm May 1 zone forecast package, the potential for severe weather had been included in the forecast for May 2. The 420 am May 2 zone forecast package also included the mention of severe weather, as well as enhanced wording highlighting the potential for damaging winds and large hail. The Mississippi Thunderstorm Outlook issued at 1015 am May 2 used wording to indicate that severe weather was likely, and discussed the possibility of tornadoes. When the Storm Prediction Center(SPC) upgraded the severe weather risk over much of Mississippi to a high risk on their afternoon issuance of the Convective Outlook, the Mississippi Thunderstorm Outlook was updated to discuss the threat for widespread severe thunderstorms.

The most significant storm during this severe weather outbreak was a long track, steady-state supercell which moved from Morehouse Parish,LA, on the far west side of Jackson's CWA, to Oktibbeha County,MS, on the far northeast side of Jackson's CWA, between 4:15 pm and 8:15 pm on May 2 (Fig. 1). This storm produced three known tornadoes along its path, including one rated F3 on the Fujita scale, as well as baseball sized hail and wind gusts of up to 90 mph. Even though much of the storm's track was over sparsely populated areas, damage was estimated to be approximately$6.5 million.

In spite of the large amount of property damage, no injuries or deaths were reported with this storm. This is certainly due in large measure to the warning services provided by NWSFO Jackson to the affected areas. Tornado warnings were issued for every county/ parish along the storm's path (a total of 13), starting at Morehouse Parish, LA, issued at 409 pm, and ending with Oktibbeha County, MS, issued at 746 pm. Four of the 13 counties/parishes warned for had confirmed tornadoes pass through them, while 6 of the 9 other counties/parishes had some other reported severe weather occurrence. The average lead time provided between the issuance of warnings and the touchdown of tornadoes associated with this storm was 12 minutes. Additionally, Short Term Forecasts(NOW) outlining the area where the strongest convection would occur were issued 5 times in the 4 hour period during which the supercell occurred.

By far the most critical warning services provided during this event were between 6 and 7 pm when this supercell was passing through Humphreys and Holmes counties. As the storm passed through these two counties, it produced baseball sized hail and wind gusts of 90 mph in Belzoni, the county seat of Humphreys County. Here is figs 2 and 3 for radar data. Damage in the business district of Belzoni was significant, including a car dealership having the roof taken off and the windows knocked out by large hail ,destruction of a grain storage facility, damage to apartment complex roofs, and numerous trees downed on structures.

The figure 2 image shows the storm near Belzoni. Circles indicate positions of radar identified circulations/mesocyclones, and triangles with numbers indicate radar estimated hail sizes.

 

 

Jackson WSR-88D Reflectivity Cross Section (Fig 3) from 2311 UTC(6:11 pm) for storm near Belzoni

 

Just after the storm passed into Holmes County from Humphreys, a tornado developed with it (Fig. 4 for radar data). Before passing near the town of Tchula, MS, the tornado strengthened to an F3 on the Fujita scale. At this time, it struck and virtually destroyed S.V. Marshall School. Luckily, classes were not in session at the time, although a few people were in the school building when the storm struck. A newspaper article Fig 5 stated that spring football practice would have been in progress had it not been cancelled due to forecasts of severe weather. Shortly after the tornado struck the school, several houses and mobile homes just to the northeast of the school were damaged or destroyed.

Figure 5: This Figure is showing the Storm Relative Wind Velocity.

 

In spite of the heavy damage to the Belzoni business district, the Tchula school, and the homes northeast of the Tchula school, no injuries or deaths occurred with this supercell. The main reason for this is likely the warning services provided. A tornado warning was issued for Humphreys County 18 minutes prior to the damage at Belzoni, and a tornado warning was issued for Holmes County 19 minutes prior to the tornado near Tchula touching down. When a storm survey of the area was conducted over the days following this event, many people were interviewed about warning services. Without exception,every person interviewed said that they had been aware that a tornado warning was in effect, and had taken shelter. Many felt that this was the principal reason they had come through the incident unscathed.

Warnings issued along the path of the supercell highlighted towns where the tornadic circulation would pass close to, as well as other threats such as large hail and damaging winds. The tornado warning issued for Holmes County specifically mentioned the town of Tchula as in the path of the storm. It should be noted that tornado warnings were carried along the path of this storm mainly based on Doppler radar indications, as real time damage reports were quite limited and delayed, especially as the storm was moving through the sparsely populated areas just to the west of Humphreys County. However, what reports were received were used to highlight the threat to the public by insertion into warnings or quickly issued severe weather statements. Another point to keep in mind is that several other intense storms were ongoing at the time of the damage to Holmes and Humphreys counties. In fact, warnings were issued for 12 other counties during the time that the main supercell was impacting Holmes and Humphreys counties.

In conclusion this weather event obviously had a major impact on the lives of the people it affected. Without the warning and forecast services provided by NWSFO Jackson, injuries and/or deaths would likely have occurred.

 

 


 

 

    Staffing During the Evening of May 2, 1997(during the main supercell)

  • Alan Gerard(Senior Forecaster)-Shift Supervisor,(Severe Weather Co-ordinator) Warning Composer
  • Edward Agre(Senior Forecaster)-Warning Decision Support System(WDSS) Meteorologist(Columbus AFB WSR-88D)
  • Marc McAllister(Forecaster)-WSR-88D Meteorologist (4 pm til 8 pm)
  • Gregory Garrett(Senior Forecaster)-WSR-88D Meteorologist (8 pm til Midnight)
  • Rusty Pfost(Science and Operations Officer)-Coordination phone calls, Assist with issuing warnings
  • Bradley Regan(Forecaster)-Public Forecaster (Zone Forecasts, Forecast Discussions,etc.)
  • Steven Miller(Met Intern)- Aviation Forecaster, Short Term Forecasts
  • Johnny Baxter(Hydrometeorological Technician)- ASOS/Upper Air/Public Service
  • William Knight(Data Acquisition Program Manager)- Assist with ASOS/Upper Air/Public Service
  • Corey Mead (Met Intern)- NOAA Weather Radio(NWR) Operator

 

 

Chronology of Events Associated with Main Supercell Storm

 

 

 

 

           Short Fuse Warnings/Statements

 

 

 

Picture of Tchula School Storm Damage

 

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