Severe weather event in April 1979
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On Tuesday, April 10, 1979, a widespread and destructive outbreak of severe weather impacted areas near the Red River between Oklahoma and Texas. Thunderstorms developed over West and North Central Texas during the day within highly unstable atmospheric conditions following the northward surge of warm and moist air into the region, producing large hail, strong winds, and multiple tornadoes. At least 22 tornadoes were documented on April 10, of which two were assigned an F4 rating on the Fujita scale; four of the tornadoes caused fatalities.
Hardest hit were the communities of Vernon, Texas; Lawton, Oklahoma; and Wichita Falls, Texas, which were all impacted by strong tornadoes. The F4 Vernon tornado struck southern and eastern parts of the city at approximately 4:45 p.m. CST, destroying several residential blocks and killing 11 people. An F3 tornado spun up in Lawton at 5:05 p.m. CST, destroying 167 buildings and killing 3 people. The most significant tornado of the day was an F4 tornado that began east-northeast of Holliday, Texas, at around 5:50 p.m. CST and moved east-northeast into Wichita Falls, taking a course through densely-populated areas of the city and destroying over two thousand homes across several neighborhoods. The tornado spanned as wide as across during its passage through the city, with the most severe damage occurring within a wide swath. At least 45 people were killed within the city and nearly 1,800 people were injured, ranking the tornado among the deadliest in Texas history. A majority of the fatalities occurred as the tornado mangled and tossed vehicles. The damage wrought by the Wichita Falls tornado was unprecedented, with the $400 million damage toll making it the costliest tornado on record at the time. The severe weather event was widely observed by scientific instruments due to its serendipitous occurrence during a NASA field campaign. Later studies referred to the tornado outbreak as the Red River Valley Tornado Outbreak, and in the areas affected the day came to be known as Terrible Tuesday.
The same weather system associated with the tornado outbreak produced additional thunderstorms and tornadoes on April 11, particularly in Arkansas. While tornadic activity was more widespread on April 11 compared to April 10 far fewer casualties occurred. The weather system also produced intense rainfall over Mississippi and Alabama that culminated in the 1979 Easter flood, the worst disaster to befall Jackson, Mississippi in over a century.
Meteorological synopsis.
Preceding the event.
On April 9, a strong upper-tropospheric trough was located over the western United States. At roughly above the surface, a powerful jet stream extended from the eastern Pacific to South Texas. Although a cold front moving south during the day brought substantially cooler conditions to Oklahoma, it quickly weakened over Texas. Warm and moist air remained over South Texas ahead of the disturbances. Meteorological computer models using data collected at 6 p.m. CST April 9 suggested that severe weather was possible the next day for parts of Oklahoma and Texas but did not as indicate as clearly the possibility of a tornado outbreak. The upper-tropospheric trough moved slower than modeling projected and by 6:00 a.m. CST April 10 had become oriented north-northeast to south-southwest, a characteristically negative tilt associated with many severe weather outbreaks. An occluded front stretched from a quickly intensifying low-pressure area in Colorado into the Texas Panhandle, representing one area conducive to storm development. A wide expanse of stratus clouds covered much of Central Texas during the morning hours as a result of a stable airmass over the area. However, strong southerly winds closer to the surface brought moisture northward from South Texas, concurrent with a rapid increase in atmospheric instability over North Texas. Due to the presence of directional wind shear, the winds over the Red River Valley brought moist air from the south closer to the surface, and drier air from the west further aloft, enhancing convective instability. The leading edge of the northward surge of moisture was marked by an ill-defined warm front. Dew points across the region increased by around to near .
A line of thunderstorms developed over North Texas on the morning of April 10 in response to the surge of warm air, with small hail up to diameter associated with some of the storms. Within the nearby jet stream, an area of locally intense winds – a jet streak – moved towards the northeast towards the expanding unstable airmass over north-central Texas. The passage of this core of intense winds aloft induced strong southwesterly winds closer to the surface over eastern New Mexico and West Texas, leading to widespread blowing dust. Wind gusts exceeded across West Texas and reached as high as at Guadalupe Mountains National Park. The dew point at Marfa, Texas, was compared to dew points near over central Texas. This surge of dry air, moving towards the east-northeast at roughly , marked another potential region for storm development. A second area of thunderstorms began to quickly intensify along the leading edge of this dry line and along the occluded front between Amarillo, Texas, and Plainview, Texas. Hail up to in diameter was reported in association with these storms, as well as a tornado east of Plainview at around 1:38 p.m. CST that caused no damage. A third area of thunderstorms, albeit short-lived, developed west of Abilene, Texas, along the western edge of a small region of high pressure. While several of the morning's storms moved towards stable conditions and were poised to eventually weaken, particularly conducive conditions for intense thunderstorm development materialized near Lubbock, Texas, at the intersection of the surging dry line, the warm front, and the western edge of the high pressure region.
By the afternoon of April 10, both the warm front and the region of strong winds associated with the jet stream had reached the Red River area, resulting in stronger wind shear. A low-pressure area had also developed in the vicinity of Childress, Texas at around 1–2 p.m. CST, and would serve as a focusing mechanism for converging moisture over the Red River Valley. The National Severe Storms Forecasting Center (NSSFC) issued a tornado watch at 1:55 p.m. CST on April 10 for a area encompassing parts of southwestern Oklahoma and north-central Texas. The watch statement highlighted the potential for tornadoes, large hail, and damaging winds within the watch area. Within the risk region, the air pressure fell by in three hours; such drastic pressure falls can precede tornado outbreaks. Strong convergence of moisture was also observed in the areas where storms eventually formed.
Tornado outbreak.
The arrival of the jet streak contributed to the conversion of the atmospheric instability accumulating near the Red River into thunderstorm formation. Just before the onset of the tornado outbreak, a low level jet with winds of materialized over north-central Texas in response to the approach of the jet streak higher aloft, accelerating the transport of heat and moisture northward into the Red River Valley. Thunderstorms developed near Lubbock and moved east-northeastward into a region of high potential instability near the Red River, becoming the strongest thunderstorms of the day. In particular, three isolated supercell thunderstorms caused the majority of the severe weather during the afternoon and evening of April 10; all developed in the localized area of supportive conditions near the frontal intersection. The first thunderstorm formed around 1:00 p.m. CST spawned five tornadoes between 3:05 p.m. CST and 5:15 p.m. CST, including an F4-rated tornado that struck Vernon, Texas, and an F3-rated tornado that struck Lawton, Oklahoma. The second thunderstorm formed around 2:30 p.m. CST, while the third formed around 4:30 p.m. CST. The second supercell produced a tornado that began at 3:55 p.m. and took long track – the longest track of any tornado during the event – through primarily rural areas near Harrold, Texas and Grandfield, Oklahoma. The most damaging tornado, associated with the third supercell, began at around 5:55 p.m. CST and struck Wichita Falls, Texas. These storms persisted into nighttime over central and eastern Oklahoma. The breakout of severe weather and tornadoes associated with the thunderstorms near the Red River during the afternoon and evening of April 10 was collectively termed the "Red River Valley outbreak" or the "Red River Valley tornado outbreak" by scientists studying the event. At least 12 tornadoes occurred within of Wichita Falls in a single two-hour period. The last tornado that occurred in the Red River Valley occurred around 8:00 p.m. CST in connection with the third supercell near Pruitt City, Oklahoma. The thunderstorms that produced the tornadoes in the Red River Valley continued into Arkansas and southern Missouri during the overnight hours but did not produce severe weather.
The arrival of a second and weaker region of strong winds within the nearby jet stream led to the development of severe thunderstorms, including some tornadoes, farther south over west-central and northern Texas during the overnight hours. These tornadoes caused extensive damage in rural areas and some injuries. Like the severe event earlier in the day along the Red River, the development of these storms was aided by a localized area of low pressure that developed near Abilene at around 7:20 p.m. CST. Additional storms also persisted over the Midwestern United States into the morning of April 11. The broader weather system that produced the severe weather on April 10 continued eastward towards the Mississippi River Valley the next day and intensified. April 11 ultimately proved to be a more active day for severe weather, with Arkansas experiencing most of the day's tornadoes; however, fewer casualties resulted from the tornadoes compared to the previous day. The 27 tornadoes that were ultimately documented by the National Oceanic and Atmospheric Administration in Arkansas during April 1979 set a new monthly record high for the state. Heavy rains over Mississippi and Alabama associated with the same weather system on April 11–13 led to extensive flooding along the banks of the Pearl River and Tombigbee River. Rainfall totals reached , with the flood near Jackson, Mississippi, being representative of a 1 in 500-year or 1 in 100-year flood event.
Confirmed tornadoes.
NWS offices in Texas and Oklahoma reported 56 fatalities from the tornadoes on April 10, with 53 in Texas and 3 in Oklahoma across a combined 12 counties. Another 1,916 people were injured, of which 256 were hospitalized. The American Red Cross reported 2,934 homes destroyed with another 3,263 damaged. April 10 featured the most damaging tornado outbreak since the 1974 Super Outbreak. Four tornadoes caused fatalities that day. The NWS characterized the tornado outbreak as "one of the most significant tornado outbreaks that ever occurred in western north Texas and southern Oklahoma." The atmospheric environment surrounding the April 10 severe weather outbreak and the thunderstorms that eventually formed were closely observed as part of the Severe Environmental Storms and Mesoscale Experiment (SESAME), a scientific field campaign aimed at studying severe weather. As part of SESAME, an extensive survey of affected areas was undertaken following the event, including interviews of civil defense directors and ground and aerial surveys of tornado paths. Damage along the paths of 12 of the tornadoes on April 10 were rated with the Fujita scale by Ted Fujita and Roger Wakimoto based on observations from a low-flying Cessna aircraft on April 12–13, with a presumed ±1 margin of error.
Thalia–Vernon, Texas/Davidson, Oklahoma.
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The first of three intense and tornadic thunderstorms produced a tornado in southern Foard County, Texas, at 2:05 p.m. CST. While this first tornado was still on the ground, the same thunderstorm produced a second tornado in Foard County so north of Thalia, at around 3:20 p.m. CST; the two tornadoes were separated by and moved in parallel for . The second tornado continued into Wilbarger County, after the first dissipated. It tracked towards the Lockett, area along US 70, damaging farms and homes. Fujita and Wakimoto assessed up to F2-rated tornado damage between Thalia and Lockett. The tornado crossed the highway north of Lockett. One person was killed by the tornado after their vehicle was blown off US-70 into a pasture.
The tornado then moved northeast towards the Vernon, area. Its large size made identification of its tornadic nature by storm spotters difficult. Tornado sirens were activated shortly before the tornado struck Vernon. The tornado entered Vernon at around 3:45 p.m. CST and moved over southern and eastern parts of the city. Several residential blocks in southern Vernon were destroyed by the tornado, leading to at least three deaths. The damage was especially severe along Gordon and Atlanta streets. In eastern Vernon, the tornado razed several buildings, including the Wilbarger Exhibit Building and a Texas Highway Department warehouse. The tornado then crossed US 287, blowing vehicles off the highway and