From May 2–5, 1999, a large, historic, and devastating tornado outbreak took place across much of the Central United States, causing catastrophic impacts. During this three-day event, 141 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, in what is referred to as the May 3 outbreak, or more officially by the National Weather Service (NWS) and NOAA as the Great Plains Tornado Outbreak of May 3–4, 1999, or the Oklahoma/Kansas tornado outbreak. 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.
In 2023, tornado expert Thomas P. Grazulis published the outbreak intensity score (OIS) as a way to rank outbreaks. The outbreak received 145 OIS points, ranking it as a historic tornado outbreak.
Meteorological synopsis
On the morning of May 3, in its Day 1 Convective Outlook for the United States, the Storm Prediction Center (SPC) – based in Norman, approximately south of the tornado's eventual damage path – issued a slight risk of severe thunderstorms from southern Nebraska to central Texas. SPC analysis had detected the presence of a dry line that stretched from western Kansas into western Texas that was approaching a warm, humid air-mass over the Central Plains; the condition ahead of the dry line and a connecting trough positioned over northeastern Colorado appeared to favor the development of thunderstorms later that day that would contain large hail, damaging straight-line winds, and isolated tornadoes.
SPC forecasters initially underestimated the atmospheric conditions that would support tornadic development that afternoon and evening. Around 4:00 a.m. CDT that morning, Doppler radar and wind profile data indicated a streak of elevated jet stream winds along the California−Nevada border, though weather balloon soundings sent up the previous evening by National Weather Service (NWS) offices in the western U.S. and numerical computer model data failed to detect the fast-moving air current as it moved ashore from the Pacific Ocean. In addition, the dry line was diffused, with surface winds behind and ahead of the boundary moving into the region from a southerly direction. SPC meteorologists began to recalculate model data during the morning to account for the stronger wind profiles caused by the jet streak; the data acknowledged that thunderstorms would occur within the Central Plains, but disagreed on the exact area of greatest severe weather risk.
By 7:00 a.m. CDT, CAPE (convective available potential energy) values began exceeding 4,000 J/kg, an extreme value well above the climatological threshold favoring the development of severe thunderstorms. Despite conflicting model data on the specified area where thunderstorms would develop, the newly available information that denoted a more favorable severe thunderstorm setup in that part of the state prompted the SPC to upgrade the forecasted threat of severe weather to a moderate risk for south-central Kansas, much of the western two-thirds of Oklahoma, and the northwestern and north-central portions of Texas at 11:15 a.m. CDT that morning, which now indicated that the atmospheric conditions present would "provide sufficient shear for a few strong or violent tornadic supercells given the abundant low level moisture and the high instability." The increasing threat of a severe weather/tornado outbreak for late that afternoon into the evening was reemphasized by NWS Norman forecasters in a Thunderstorm Outlook issued by the office at 12:30 p.m. CDT.
By the early afternoon, forecasters at both the SPC and NWS Norman forecast office (both of which shared an office complex near Max Westheimer Airport at the time), realized that a major event was likely to take place based solely on observational data from radar and weather satellite imagery and balloon soundings, as the computer models remained uncooperative in helping meteorologists determine where the greatest threat of severe storms would occur.
Conditions became highly conducive for tornadic development by 1:00 p.m. CDT as wind shear intensified over the region (as confirmed by an unscheduled balloon sounding flight conducted by the NWS Norman office), creating a highly unstable atmosphere. The sounding balloon recorded winds blowing southwesterly at respectively at the surface and at the level, southerly winds of and westerly winds of at ; it also indicated that a capping inversion over the region was weakening in southwestern Oklahoma and north Texas. With the warm air above the surface cooling down, this allowed warm air at the surface the chance to rise and potentially create thunderstorms. Although cirrus clouds − a bank of which had developed in west Texas and overspread portions of Oklahoma later in the morning − were present through much of the day, an area of clearing skies over western north Texas and southwestern Oklahoma early that afternoon allowed for the sun to heat up the moisture-laden region, creating significant atmospheric instability.
At 3:49 p.m. CDT, the SPC − having gathered enough data to surmise that there was a credible threat of a significant severe weather outbreak occurring within the next few hours − amended its Day 1 Convective Outlook to place the western nine-tenths of the main body of Oklahoma, central and south-central Kansas and the northern two-thirds of Texas under a high severe weather risk, denoting a higher than normal probability of strong (F2+) tornadoes within the risk area. About 40 minutes after the revised outlook's issuance, at 4:30 p.m. CDT, the SPC issued a tornado watch for western and central Oklahoma, effective from 4:45 p.m. until 10:00 p.m. CDT that evening, for the threat of tornadoes, hail up to in diameter, wind gusts to and intense lightning. As that happened, the first thunderstorm cell of the unfolding event had already formed over southwestern Oklahoma.
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 (rated as an F3) 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,However, adjustment for growth in wealth shows the May 27, 1896 Saint Louis–East Saint Louis tornado to be the costliest on record. See 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.
Wellington–Haysville–South Wichita, Kansas
This violent tornado first touched down north of Wellington, Kansas around 8:13 p.m. CDT, downing several power poles in the area, and tracked north-northeast. Along its path, two mobile homes, three sheds, and a pole barn were destroyed while nine other buildings sustained damage. Four people were injured in Sumner County, Kansas, three of which occurred when a mobile home was destroyed. About 20 minutes after touching down, the tornado crossed into Sedgwick County about west of Peck. At 8:35 p.m. CDT, the now violent tornado struck a mobile home park in Haysville, destroying much of the subdivision and killing three people. Continuing into the city's central business district, the tornado caused further damage and killed a fourth person. Throughout Haysville, 186 buildings were damaged or destroyed. Continuing into South Wichita, the tornado leveled the Lakeshore and Pacesetter mobile home parks, killing two residents. The tornado maintained a general northeast track before dissipating in the College Hill District of Northeast Wichita.
In total, the tornado killed six people in total and injured more than 145 others along its -long path. Approximately $145 million in damages were caused by the tornado, most of which came from Haysville. It was the second of two deadly twisters Haysville was severely impacted by in the 1990s, with the previous being the 1991 Andover tornado. Throughout Sedgwick County, 1,109 buildings were destroyed and 7,371 buildings were damaged, 2,456 severely.
Dover–Henessey, Oklahoma
This violent high-end F4 tornado struck the town of Dover, Oklahoma, causing US$2.5M (1999 USD) in damages, with the northern part of town taking a direct hit, damaging and destroying about one-third of the homes and buildings in town.