1999 Bridge Creek–Moore tornado

On the evening of Monday, May 3, 1999, a large and exceptionally powerful F5 tornado registered the highest wind speeds ever measured globally; winds were recorded at by a Doppler on Wheels (DOW) radar. Considered the strongest tornado ever recorded to have affected the metropolitan area, the tornado devastated southern portions of Oklahoma City, Oklahoma, along with surrounding suburbs and towns to the south and southwest. The tornado covered during its 85-minute existence, destroying thousands of homes, killing 36 people (plus an additional five indirectly), and leaving US$1 billion (1999 USD) in damage, ranking it as the fifth-costliest on record not accounting for inflation. It was the first use of the tornado emergency statement by the National Weather Service.

The tornado first touched down at 6:23 p.m. Central Daylight Time (CDT) in Grady County, roughly south-southwest of the town of Amber. It quickly intensified into a violent F4, and gradually reached F5 status after traveling , at which time it struck the town of Bridge Creek. It fluctuated in strength, ranging from F2 to F5 status before it crossed into Cleveland County where it reached F5 intensity for a third time shortly before entering the city of Moore. By 7:30 pm, the tornado crossed into Oklahoma County and battered southeastern Oklahoma City, Del City, and Midwest City before dissipating around 7:48 p.m. just outside Midwest City. A total of 8,132 homes, 1,041 apartments, 260 businesses, eleven public buildings, and seven churches were damaged or destroyed.

Large-scale search and rescue operations immediately took place in the affected areas. A major disaster declaration was signed by President Bill Clinton the following day (May 4) allowing the state to receive federal aid. In the following months, disaster aid amounted to $67.8 million. Reconstruction projects in subsequent years led to a safer, tornado-ready community. However, on May 20, 2013, nearby areas adjacent to the 1999 storm's track along with some of the same areas in the path of the tornado were again devastated by another large and violent EF5 tornado, resulting in 24 fatalities and extreme damage in the South Oklahoma City/Moore area.

Meteorological synopsis

The Bridge Creek–Moore tornado was part of a much larger outbreak which produced 71 tornadoes across five states throughout the Central Plains on May 3 alone, along with an additional 25 that touched down a day later in some of the areas affected by the previous day's activity (some of which were spawned by supercells that developed on the evening of May 3), stretching eastward to the Mississippi River Valley. The most prolific tornadic activity associated with the May 3 outbreak – and the multi-day outbreak as a whole – occurred in Oklahoma; 14 of the 66 tornadoes that occurred within the state that afternoon and evening produced damage consistent with the Fujita scale's "strong" (F2–F3) and "violent" (F4–F5) categories, which, in addition to the areas struck by the Bridge Creek–Moore tornado family, affected towns such as Mulhall, Cimarron City, Dover, Choctaw and Stroud.

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 hours, forecasters at both the SPC and NWS Norman (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 and 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.

Storm development and track

The thunderstorm that eventually produced the F5 tornado began developing around 3:20 p.m. CDT that afternoon over northeastern Tillman County (southwest of Faxon). Despite the lack of overall lift prevalent in the region, the storm formed out of a contrail-like horizontal area of convective clouds that developed during peak surface heating over southwestern Oklahoma, located well ahead of the dry line that was still positioned farther to the west, which provided enhanced lift and speed shear necessary to develop the supercell. Tracking northeast, the storm strengthened and entered Comanche County shortly after 4:00 p.m. CDT. By 4:15 p.m. CDT, the NWS Norman office issued a severe thunderstorm warning for Comanche County, as the initial storm continued to rapidly intensify over the southern half of the county; there, hail up to in diameter fell.

As the supercell's mesocyclonic rotation began to rapidly strengthen at the cloud base, a tornado warning was issued for the counties of Comanche, Caddo, and Grady at 4:50 p.m. CDT; one minute later, a small tornado roughly in diameter − the first of fourteen associated with supercell "A" (NWS Norman designated lettered names for the three tornado-producing supercells in the outbreak in storm surveys) − touched down east-northeast of Medicine Park along U.S. Route 62. Five more tornadoes developed as the storm continued northeast; a sixth one, which would be given an F3 rating, touched down a short time later and caused substantial damage in central Grady County, including some to the Chickasha Municipal Airport, where roofs were torn off of two hangars.

At 6:23 p.m. CDT, a ninth tornado associated with supercell "A" touched down about south-southwest of Amber. The tornado quickly intensified in both strength and size as it crossed Oklahoma State Highway 92, attaining F4 strength about east-northeast of Amber. It quickly became a wedge tornado, varying between in width at various points throughout the track. Damage consistent with this rating was sustained over the following of the path before striking Bridge Creek. There, it attained the highest-possible rating on the Fujita Scale, F5. A mobile Doppler weather radar recorded winds of within the tornado at Bridge Creek, the highest wind speed ever recorded on Earth. Since the record for maximum winds are reported from only non-tornadic events, however, the wind gust from Cyclone Olivia in 1996 retained the title.

Damage in Bridge Creek was extreme, as many homes were swept away completely, leaving only concrete slabs where the structures once stood. Damage surveyors noted that the remaining structural debris from some of the homes in this area was finely granulated into small fragments, and that trees and shrubs were completely debarked. A few of these homes were bolted to their foundations. Approximately 200 houses and mobile homes were destroyed, and hundreds of other structures were damaged. The Ridgecrest Baptist Church in Bridge Creek was also destroyed in the process. Extensive ground scouring occurred, and vehicles were thrown hundreds of yards from where they originated, including a mangled pickup truck that was found wrapped around a telephone pole. About of asphalt was scoured off one road.

About twelve people died in Bridge Creek, nine of whom were in mobile homes; all fatalities and the majority of injuries were concentrated in the Willow Lake and Southern Hills Additions and Bridge Creek Estates, consisting mostly of mobile homes. Over 39 people were injured in the area as well. Continuing northeastward, the tornado briefly weakened to F4 status before re-strengthening to F5 intensity as it neared the Grady- McClain County line, where a car was thrown roughly in the air, and a well-built home with anchor bolts was reduced to a bare slab. At this time, it had attained a width of , having grown to its largest width after crossing the South Canadian River, reported during the station's live coverage of the storm that the tornado was at least one mile wide, and was embedded (or "rain-wrapped") in the precipitation core associated with the main circulation, making it difficult to see.

As it was becoming clear that a particularly violent tornado was moving into some of the most densely populated areas of central Oklahoma, around 6:57 p.m. CDT, NWS Norman issued the first-ever tornado emergency for southern portions of the Oklahoma City metropolitan area. David Andra, a meteorologist at the NWS Norman office, said that, in drafting the enhanced warning, he wanted to "paint the picture o residents in the areas that were to be affected by the stormthat a rare and deadly tornado was imminent in the metro area." For its initial usage, the enhanced wording was released as part of a standalone Severe Weather Statement (NWS code: SVS), which were (and still are) normally meant to update the public on an existing tornado warning or severe thunderstorm warning. For tornado warnings, the SVS provides updated information on the approximate location of the storm's base-level rotation or, if it occurred after the initial warning was issued, a tornado reported by the public, civil defense personnel or storm spotters, or with the later advent of dual-polarization radar in the early 2010s, verified by radar-detected debris signatures. (In future issuances, tornado emergencies were issued within either the initial tornado warning issuance or an SVS providing updated information on a tornado warning already in effect.) Two minutes later, at 6:59 p.m. CDT, the SPC issued a Particularly Dangerous Situation tornado watch for much of the central third of Oklahoma, effective from 7:15 p.m. until midnight CDT on the early morning of May 4; the SPC watch product discussion noted that the extreme instability compensated for "somewhat marginal" wind shear to enhance the threat of strong to violent tornadoes.

Paralleling Interstate 44, the tornado moved into McClain County, where it crossed the highway twice at F4 intensity, killing a woman who was blown out from an underpass where she was attempting to seek shelter after being dragged down the embankment by the intense channeling winds; her 11-year-old son − with whom the woman vacated their stalled car nearby − survived, staying held tight onto the steel girders of the overpass. A man who helped the mother and son up the overpass suffered severe injuries to his leg, which was partially sliced by a highway sign thrown by the winds. At 7:10 p.m. CDT, a satellite tornado touched down over an open field north of Newcastle; it was rated as an F0 due to lack of damage. In McClain County, 38 homes and two businesses were destroyed and 40 homes, some of which were leveled at F4 intensity, were flattened; seventeen people were injured.

After crossing the Canadian River

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