1974 Super Tornado Outbreak
Posted: Wed Apr 09, 2003 4:14 pm
The tornado outbreak on April 3-4, 1974 was the largest in recorded history. There was 147 tornadoes in the U.S. with one in Ontario, Canada. There was also ninety-nine reports of severe thunderstorm hail and 82 reports of severe thunderstorm wind gusts. The tornadoes resulted in 315 fatalities and 5454 injuries. There was five or six F5 tornadoes (depending on your sources), with approximately 30 F4s. 536.2 square miles were covered by the tornadoes with the total path length at 2474.4 miles. There was forty-eight killer tornadoes with eight having a path length greater than 50 miles. Sixty-seven percent of the tornadoes were of the strong to violent category. Thirteen states were affected with the first touchdown at 1300 UTC.
A significant threat of severe weather was expected as early as April 2nd, as forecasts and model output depicted the development of a strong spring cyclone over the central Plains. The National Severe Storms Forecast Center phoned many Weather Service Offices and River Forecast Centers across the Middle and Lower Mississippi Valley to alert them to the potental for severe weather on April 3rd. This included a message for radar sites to make sure their radar and equipment was operating correctly.
A large deep cyclone did develop over Colorado late on April 2nd and moved into western Kansas by early on April 3rd. A squalline of thunderstorms developed during the early morning of April 3rd over Oklahoma and Texas, rapidly moving northeast and producing sporatic severe weather reports. The first convective watch of the day was a severe thunderstorm watch, issued for parts of the Ohio Valley, valid from 9:30 AM through 3:00 PM. This first line of storms moved east and northeast at 60 mph.
The synoptic pattern was very favorable for severe weather across the Ohio Valley, southward through Tennessee and the deep south. With the deep surface low over Kansas, a warm front extended west-east across the Ohio Valley, snaking around the southern part of the Appalachians to the North Carolina coast. Air was very moist south of this boundary (dewpoints in the 60s). This warm front lifted northward through the day with a dryline approaching and crossing the Mississippi River later in the day. Strong south winds prevailed over the warm sector at the surface, with southwest winds increasing to 40-50 knots at 5000 feet and winds above 70 knots at 20,000 feet. Low level veering of winds with height and the strong increase of speed with height created a great deal of speed and directional shearing. The approach of a 90 knot upper level jet over Texas and a 100 knot jet over the Great Lakes created a favorable difluent upper level flow. Cooling aloft, combined with strong surface heating during the afternoon, rich low level moisture, mid level drying and dynamic lifting provided by other factors helped develop severe thunderstorms during the afternoon of April 3rd.
Thunderstorms that moved into the Appalachians with the initial line weakened, while cloud cover broke farther west. New storms developed from northeast Arkansas to southwest Indiana by late morning, increasing in intensity through early afternoon. A second line of severe thunderstorms would develop from north-central Illinois to near the St. Louis area by early afternoon. These two lines of storms would soon evolve into supercells, producing tornadoes over Illinois, Indiana and Kentucky. The storms that were over southwest Indiana to Arkansas would move northeast and spread into northwest Ohio through eastern Indiana to western Kentucky and Middle Tennessee by middle afternoon. At the same time, the Illinois storms would continue to grow, with a 3rd line of storms developing from southeast Kentucky, through eastern Tennessee to west-central Alabama. According to the 2035 UTC radar summary, there was three lines of supercell thunderstorms east of the Mississippi River, with many producing tornadoes. Some of the storms showed echo tops of 60,000 feet and even higher on local radars. An uncommon occurrance happened at around 2000 UTC. The Cincinnati WSR-57 (Weather Surviellence Radar 1957) radar depicted 4 supercells on the 125 nautical mile scope, with three of those showing hook echo appendages. Also at this time, the three supercells with hook echoes were producing tornadoes over Indiana, one near Depaw, second near Greensburg and the third producing a tornado over Kennard. The forth supercell was developing just south of Dayton, Ohio. About 40 minutes later, this last cell would produce a violent tornado that would destory much of Xenia, Ohio. The storm over Depaw, Indiana would produce an F5 tornado there, as well as at Saylor Park, Ohio a few hours later. The leading edge of a storm over western Kentucky was just coming onto the scope, about 60 miles southwest of Louisville. This storm would produce the Brandenburg and Louisville tornadoes.
Numerous thunderstorms, many supercells would be located by early evening across the Ohio Valley, through Tennesee and Alabama, Mississippi, Georgia and te southern Appalachians. The strongest tornadoes over Tennessee, Alabama and Mississippi would occur around this time. Many of these cells would move to the northeast at 50 to 60 miles per hour, giving little time for residents to take shelter. Severe thunderstorms would continue into the night along the Appalachians into the deep south with additional tornadoes in West Virginia, Virginia and North Carolina.
Let me know if you have any questions.
Links:
http://www.april31974.com/
http://www.shorstmeyer.com/tornadoes/index.html
http://lwf.ncdc.noaa.gov/oa/climate/ext ... s0499.html (PDF format Synoptic Report from 1975 and satellite images, and a large map)
http://www.srh.noaa.gov/bmx/storm_surve ... index.html
http://www.erh.noaa.gov/er/iln/supoutbr.htm
http://www.interaxs.net/pub/hgr/tornado.htm
http://www.joelkammeyer.com/xenia/
http://www.publicaffairs.noaa.gov/storms/
A significant threat of severe weather was expected as early as April 2nd, as forecasts and model output depicted the development of a strong spring cyclone over the central Plains. The National Severe Storms Forecast Center phoned many Weather Service Offices and River Forecast Centers across the Middle and Lower Mississippi Valley to alert them to the potental for severe weather on April 3rd. This included a message for radar sites to make sure their radar and equipment was operating correctly.
A large deep cyclone did develop over Colorado late on April 2nd and moved into western Kansas by early on April 3rd. A squalline of thunderstorms developed during the early morning of April 3rd over Oklahoma and Texas, rapidly moving northeast and producing sporatic severe weather reports. The first convective watch of the day was a severe thunderstorm watch, issued for parts of the Ohio Valley, valid from 9:30 AM through 3:00 PM. This first line of storms moved east and northeast at 60 mph.
The synoptic pattern was very favorable for severe weather across the Ohio Valley, southward through Tennessee and the deep south. With the deep surface low over Kansas, a warm front extended west-east across the Ohio Valley, snaking around the southern part of the Appalachians to the North Carolina coast. Air was very moist south of this boundary (dewpoints in the 60s). This warm front lifted northward through the day with a dryline approaching and crossing the Mississippi River later in the day. Strong south winds prevailed over the warm sector at the surface, with southwest winds increasing to 40-50 knots at 5000 feet and winds above 70 knots at 20,000 feet. Low level veering of winds with height and the strong increase of speed with height created a great deal of speed and directional shearing. The approach of a 90 knot upper level jet over Texas and a 100 knot jet over the Great Lakes created a favorable difluent upper level flow. Cooling aloft, combined with strong surface heating during the afternoon, rich low level moisture, mid level drying and dynamic lifting provided by other factors helped develop severe thunderstorms during the afternoon of April 3rd.
Thunderstorms that moved into the Appalachians with the initial line weakened, while cloud cover broke farther west. New storms developed from northeast Arkansas to southwest Indiana by late morning, increasing in intensity through early afternoon. A second line of severe thunderstorms would develop from north-central Illinois to near the St. Louis area by early afternoon. These two lines of storms would soon evolve into supercells, producing tornadoes over Illinois, Indiana and Kentucky. The storms that were over southwest Indiana to Arkansas would move northeast and spread into northwest Ohio through eastern Indiana to western Kentucky and Middle Tennessee by middle afternoon. At the same time, the Illinois storms would continue to grow, with a 3rd line of storms developing from southeast Kentucky, through eastern Tennessee to west-central Alabama. According to the 2035 UTC radar summary, there was three lines of supercell thunderstorms east of the Mississippi River, with many producing tornadoes. Some of the storms showed echo tops of 60,000 feet and even higher on local radars. An uncommon occurrance happened at around 2000 UTC. The Cincinnati WSR-57 (Weather Surviellence Radar 1957) radar depicted 4 supercells on the 125 nautical mile scope, with three of those showing hook echo appendages. Also at this time, the three supercells with hook echoes were producing tornadoes over Indiana, one near Depaw, second near Greensburg and the third producing a tornado over Kennard. The forth supercell was developing just south of Dayton, Ohio. About 40 minutes later, this last cell would produce a violent tornado that would destory much of Xenia, Ohio. The storm over Depaw, Indiana would produce an F5 tornado there, as well as at Saylor Park, Ohio a few hours later. The leading edge of a storm over western Kentucky was just coming onto the scope, about 60 miles southwest of Louisville. This storm would produce the Brandenburg and Louisville tornadoes.
Numerous thunderstorms, many supercells would be located by early evening across the Ohio Valley, through Tennesee and Alabama, Mississippi, Georgia and te southern Appalachians. The strongest tornadoes over Tennessee, Alabama and Mississippi would occur around this time. Many of these cells would move to the northeast at 50 to 60 miles per hour, giving little time for residents to take shelter. Severe thunderstorms would continue into the night along the Appalachians into the deep south with additional tornadoes in West Virginia, Virginia and North Carolina.
Let me know if you have any questions.
Links:
http://www.april31974.com/
http://www.shorstmeyer.com/tornadoes/index.html
http://lwf.ncdc.noaa.gov/oa/climate/ext ... s0499.html (PDF format Synoptic Report from 1975 and satellite images, and a large map)
http://www.srh.noaa.gov/bmx/storm_surve ... index.html
http://www.erh.noaa.gov/er/iln/supoutbr.htm
http://www.interaxs.net/pub/hgr/tornado.htm
http://www.joelkammeyer.com/xenia/
http://www.publicaffairs.noaa.gov/storms/
