1999 Oklahoma tornado outbreak
The 1999 Oklahoma tornado outbreak was a large, historic, and devastating tornado outbreak that took place across much of the Central United States, with most tornadoes occurring from May 2–5, 1999; scattered activity occurred afterwards until May 8 in parts of the Eastern United States, as well as southern Canada. During this week-long event, 152 tornadoes touched down in these areas. The most dramatic events unfolded during the afternoon of May 3 through the early morning hours of May 4 when more than half of these storms occurred. Oklahoma experienced its largest tornado outbreak on record from this event, with 70 confirmed. The most notable of these was the F5 Bridge Creek–Moore tornado which devastated Oklahoma City and suburban communities. The tornado killed 36 people and injured 583 others; losses amounted to $1 billion, making it the first billion-dollar tornado in history. Overall, 50 people lost their lives during the outbreak and damage amounted to $1.4 billion.
On May 2, a strong area of low pressure moved out of the Rocky Mountains and into the High Plains, producing scattered severe weather and ten tornadoes in Nebraska. The following day, atmospheric conditions across Oklahoma became significantly more favorable for an outbreak of severe weather. Wind profiles across the region strongly favored tornadic activity, with the Storm Prediction Center stating, "it became more obvious something major was looming" by the afternoon. Numerous supercell thunderstorms developed across the state as well as bordering areas in Kansas and Texas. Over the following 48 hours, May 3–4, 116 tornadoes touched down across the Central United States. Following the extensive outbreak, activity became increasingly scattered from May 5 to 8, with 26 tornadoes touching down across the Eastern United States and Quebec.
In 2023, tornado expert Thomas P. Grazulis published the outbreak intensity score as a way to rank outbreaks. The outbreak received 145 OIS points, ranking it as a historic tornado outbreak.
Meteorological synopsis
The outbreak was caused by a vigorous upper-level trough that moved into the Central and Southern Plains states on the morning of May 3. That morning, low stratus clouds overspread much of Oklahoma, with clear skies along and west of a dry line located from Gage to Childress, Texas. Air temperatures at 7:00 a.m. Central Daylight Time ranged in the mid to upper 60s °F across the region, while dew point values ranged in the low to mid 60s °F. The Storm Prediction Center in Norman, Oklahoma, a division of the National Weather Service, initially issued a slight risk of severe thunderstorms early that morning stretching from the Kansas-Nebraska border to parts of southern Texas, with an intended threat of large hail, damaging winds and tornadoes.File:Radar May 3, 1999 KTLX.gif|thumb|250px|Depicts radar imagery taken by the National Weather Service NEXRAD radar, KTLX, in Central Oklahoma during the May 1999 tornado outbreak. This imagery is from May 3.
By late morning, the low cloud cover began to dissipate in advance of the dry line, but during the afternoon high cirrus clouds overspread the region, resulting in filtered sunshine in some areas that caused atmospheric destabilization. The sunshine and heating, combined with abundant low-level moisture, combined to produce a very unstable air mass. Upper air balloon soundings observed strong directional wind shear, cooling temperatures at high atmospheric levels, and the increased potential of CAPE values potentially exceeding 4000 J/kg, levels that are considered favorable for supercells and tornadoes.
As observations and forecasts began to indicate an increasing likelihood of widespread severe weather conditions even more favorable for strong tornadoes, the SPC issued a moderate risk of severe weather at 11:15 a.m. CDT for portions of Kansas, Oklahoma and Texas along and near the Interstate 40 corridor. By 3:00 p.m. CDT, it had become evident that a widespread severe weather event was imminent; the Storm Prediction Center upgraded locations within the moderate risk area to a high risk of severe weather around 4:00 p.m. CDT as wind shear profiles, combined with volatile atmospheric conditions, had made conditions highly conducive for a significant tornadic event across most of Oklahoma, southern Kansas and north Texas, including the likelihood of violent, damaging tornadoes. The SPC issued a tornado watch by mid-afternoon as conditions gathered together for what would be a historic tornado outbreak. By the time thunderstorms began developing in the late afternoon, CAPE values over the region had reached to near 6,000 J/kg. Large supercell thunderstorms developed, and in the late afternoon through the mid-evening hours of that Monday, tornadoes began to break out across the state.
Confirmed tornadoes
Bridge Creek–Moore, Oklahoma
At approximately 3:30 p.m. CDT, a severe thunderstorm began forming in Tillman County in southwestern Oklahoma; a severe thunderstorm warning was issued for this storm by the National Weather Service Weather Forecast Office in Norman at 4:15 p.m. CDT. The storm quickly developed supercell characteristics and began exhibiting potentially tornadic rotation, resulting in the National Weather Service issuing the first tornado warning of the event for Comanche, Caddo, and Grady counties approximately 35 minutes later at 4:50 p.m. CDT.The first tornado from this supercell touched down east-northeast of Medicine Park at 4:51 p.m. CDT; it produced four additional tornadoes as it tracked northeast into Caddo County, the strongest of which touched down west-southwest of Laverty and dissipated west-northwest of downtown Chickasha. This large tornado had exhibited a companion satellite tornado for a few minutes.
The storm produced the most significant tornado of the outbreak, which touched down just southwest of the Grady County community of Amber at 6:23 p.m. CDT and headed northeast, parallel to Interstate 44, just after another tornado had passed over the airport in Chickasha. The storm continued moving northeast, destroying the community of Bridge Creek and crossing I-44 just north of Newcastle. The tornado then crossed the Canadian River, passing into far southern Oklahoma City. As it passed over Bridge Creek, around 6:54 p.m., a Doppler On Wheels mobile Doppler weather radar detected wind speeds of – later revised to – inside the tornado at an elevation of. These winds, however, occurred above the ground, and winds at the surface may not have been quite this intense. The tornado continued on into Moore, then passed over the intersection of Shields Boulevard and Interstate 35 and back into Oklahoma City, crossing Interstate 240 near Bryant Avenue. The storm then turned more northerly, striking parts of Del City and Tinker Air Force Base near Sooner Road as an F4. The storm damaged and/or destroyed several businesses, homes and churches in Midwest City. Some damage in this area was rated as high-end F4, although F5 was considered. The tornado diminished over Midwest City and finally lifted near the intersection of Reno Avenue and Woodcrest Drive.
Thirty-six people died in this tornado, and over 8,000 homes were badly damaged or destroyed. The tornado caused $1 billion in damage, making it the second-costliest tornado in U.S. history, and the most costly in history from 1999 to 2011, at which point it was surpassed by the 2011 Tuscaloosa–Birmingham tornado and again by the 2011 Joplin tornado. It was also the deadliest tornado to hit the U.S. since the April 10, 1979 F4 tornado that hit Wichita Falls, Texas, which killed 42 people.
Cimarron City–Mulhall–Perry, Oklahoma
Late in the evening on May 3 at 9:25 p.m. CDT, this destructive tornado touched down southwest of Cimarron City in Logan County, Oklahoma, eventually hitting the town of Mulhall, located north of Guthrie. This wedge tornado, which tracked a path, was very wide and at times exceeded in width. According to storm chasing meteorologist Roger Edwards, it may have been as violent or more than the F5 Bridge Creek–Moore tornado.A Doppler On Wheels mobile radar observed this tornado as it crossed Mulhall. The DOW documented the largest-ever-observed core flow circulation with a distance of between peak velocities on either side of the tornado, and a roughly width of peak wind gusts exceeding, making the Mulhall tornado the largest tornado ever measured quantitatively. The DOW measured a complex multi-vortex structure, with several vortices containing winds of up to rotating around the tornado. The 3D structure of the tornado has been analyzed in a 2005 article in the Journal of the Atmospheric Sciences by Wen-Chau Lee and Joshua Wurman. The tornado severely damaged or destroyed approximately 60–70% of the 130 homes in Mulhall, destroying the Mulhall/Orlando Elementary School and toppling the city's water tower.
After the tornado dissipated at approximately 10:45 p.m. CDT in southeastern Noble County, northeast of Perry, many of the same areas of Logan County struck by the Mulhall tornado were hit again by an F3 tornado. However, this one was produced by a separate supercell that touched down south of Crescent at 10:56 p.m. CDT. Damage caused by this tornado was indistinguishable from damage caused by the earlier F4 tornado. 25 homes were destroyed and 30 others were damaged near Crescent, with much of the damage believed to have been caused by both tornadoes.
Stroud, Oklahoma
At 10:10 p.m. CDT, this intense and damaging tornado touched down north-northeast of Sparks in Lincoln County, Oklahoma, with only sporadic tree damage occurring as it tracked north-northeast toward Davenport. Scattered damage of high-end F0 to low-end F1 intensity occurred to some homes and businesses on the southeast side of Davenport, though a house located just south of town lost more than half of its roof. As the tornado continued to track northeast, parallel with Interstate 44 and State Highway 66, Stroud took a direct hit as the storm intensified to F2 strength; the trucking terminal of the Sygma food distribution warehouse on the west side of town was destroyed with some girders and siding from the warehouse thrown northwest across State Highway 66, and the Stroud Municipal Hospital suffered significant roof damage, which resulted in significant water damage within the building. The most severe damage, consistent with an F3 tornado, occurred at the Tanger Outlet Mall at 10:39 p.m. CDT with almost all of the stores suffering roof damage at minimum, though sections of seven storefronts were destroyed and the exterior walls of the Levi's store were collapsed inward. The mall was evacuated in advance of the tornado, resulting in no injuries or loss of life in the building. The tornado finally dissipated south of Stroud Lake at 10:50 p.m. CDT.While there were no fatalities overall in Stroud, the economic impact of the tornado has been compared to the loss of Tinker Air Force Base, General Motors, and a major regional hospital for the Stroud region as compared to Oklahoma City at that time. Approximately 800 jobs were lost in a community of approximately 3,400 people due to the damage of the Sygma distribution warehouse and Tanger Outlet Mall, neither of which were rebuilt. Stroud's recovery was later complicated by the September 11, 2001, terrorist attacks, although the town has since recovered as a result of higher oil and gas prices. Local leading industries include Service King, an oilfield manufacturing facility, and Mint Turbines, a helicopter engine reconditioning facility. Stroud is also now a downloading facility location for oil produced in the northern United States into the Cushing pipeline network.