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1999 Oklahoma tornado outbreak

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Date of tornado outbreak:	May 3-6 1999
Duration1:	~72 hours
Maximum rated tornado2:	F5 tornado
Tornadoes caused:	140
Damages:	$1.9 billion (2007 USD)
Fatalities:	50
Areas affected:	Oklahoma, Kansas, Texas, Tennessee
1Time from first tornado to last tornado 2Most severe tornado damage; see Fujita Scale

The 1999 Oklahoma tornado outbreak was a severe weather event that lasted from May 3 until May 6, 1999 and brought violent storms to Oklahoma, Kansas, Arkansas, and Tennessee. This article concentrates on the events on May 3, when 66 tornadoes broke out in Oklahoma and Kansas. The most significant tornado first touched down southwest of Chickasha, Oklahoma, and became an F5 before dissipating over Midwest City, Oklahoma. The tornado tore through Bridge Creek, Oklahoma and Moore, Oklahoma, causing $1.1 billion in damage. Forty-eight people perished during the outbreak. This tornadic event ranks in severity with the Palm Sunday tornado outbreak of 1965. With a total of 66-74 tornadoes, it was the most prolific tornado outbreak in Oklahoma history, although not the deadliest.

Outbreak description

May 3, 1999 started sunny, warm, and humid across the affected region. The Storm Prediction Center in Norman, Oklahoma initially issued a "slight risk" for severe weather for most of the state of Oklahoma early that morning. By late morning the latest observations and forecasts began to indicate an increasing likelihood of widespread severe weather, and the SPC upgraded sections of the southern plains to "moderate risk." By 3 p.m. it had become evident that a widespread severe weather event was imminent. Parts of Oklahoma and Kansas were then further upgraded to "high risk". When a "high risk" is issued, this usually indicates the potential for a significant severe weather event, including 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 afternoon the CAPE values reached nearly 6,000 J/kg over the region. 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

(based on NOAA Storm Data)

The Bridge Creek-Moore F5

Path

Oklahoma City NEXRAD image at 7:12 pm. The radar shows a classic hook echo at the location of the Bridge Creek/Moore tornado.

The most significant tornado of the outbreak touched down just southwest of the community of Amber, Oklahoma and headed northeast, parallel to Interstate 44, just after another tornado had passed over the airport in Chickasha. (Note: it may be argued that the storms touching down in Chickasha and Amber were the same storm; however, for weather tracking purposes, each touchdown is counted as a separate tornado which is most probable). 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 (DOW: Wurman et al. 1997, Wurman 2001) mobile Doppler weather radar detected winds of 301 mph (484 km/h), +/- 20 mph inside the tornado at a height of 32 m AGL (Wurman et al. 2007)^[1] (The old record was a 257-268 mph wind measurement from a Doppler weather radar near Red Rock, Oklahoma, as reported in a formal publication by Bluestein et al. (1993)). 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 and 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 before diminishing over Midwest City and finally lifting near the intersection of Reno Avenue and Woodcrest Drive.

Casualties

The frame of a pickup truck wrapped around a utility pole from the Moore, Oklahoma F5 tornado

Thirty-six people died in this tornado^[2]. Over 8,000 homes were badly damaged or destroyed and the tornado caused $1.1 billion in damage, making it the single most costly tornado in U.S. history^{[citation needed]}, adjusted for inflation^[3]. This was also the deadliest tornado since the April 10, 1979 Wichita Falls, Texas Tornado which killed forty- two^[4]. However, early warning saved many lives.

Broadcast Warnings

Warnings were issued well in advance of the tornado's arrival, and the Oklahoma City broadcast media interrupted programming to follow the storms on radar and even by helicopter. The death toll would, most likely, have been higher if people had not had the benefit of the advance warning. Following the storm, three of the local television stations in Oklahoma City: KFOR-TV (channel 4), KOCO-TV (channel 5) and KWTV (channel 9) continued coverage of the damaging and deadly tornadoes through May 4. The three station's chief meteorologists Mike Morgan, Rick Mitchell and Gary England received commendations from then-governor Frank Keating for their coverage of the outbreak.Most metro area radio stations simulcast coverage from television stations. KFOR-TV was simulcast on Renda Broadcasting owned KMGL, KRXO, KOMA-AM and KOMA-FM. KOCO-TV was simulcast on Clear Channel owned KQSR, KTST and KJYO. KTOK provided their own coverage but utilized KOCO's coverage heavily. Citadel owned KATT, KYIS, WWLS-AM, WWLS-FM and KKWD simulcast KOCO-TV as well. KWTV was simulcast on Clear Channel owned KXXY-FM.

Impact

Overpass storm shelter deaths

Three of the deaths reported in the tornado were from people who took shelter underneath overpasses in the area of the path of the Moore-Bridge Creek F5 tornado. The deaths occurred at the 16th Street overpass over Interstate 44 in Newcastle (just east of Bridge Creek), at the Shields Boulevard overpass over Interstate 35 in Moore, and the overpass at mile marker 176.5 on Interstate 35 in rural northwestern Payne County, west of Stillwater.

Fujita scale

This tornado's remarkable wind speed (at the high extreme of the Fujita Scale's F5) led to much speculation that the scale would be modified to include an F6 category, due to the winds possibly exceeding 319 mph (515 km/h). This speculation ignored the fact that the Fujita scale measures damage rather than windspeed, since the scale was developed prior to the introduction of Doppler weather radar. Windspeed estimates associated with the different categories represent the speeds scientists believe are required to produce that damage rather than the windspeed in that particular storm. The damage caused by an F5-designated tornado leaves very little room for a higher category.

The tornado was the last official F5 to hit the United States with the old Fujita scale rating. The next category 5 tornado occurred on May 4, 2007 in Greensburg, Kansas during the May 2007 Tornado Outbreak and killed 11 people. Since February 1, 2007 the National Weather Service has used the Enhanced Fujita Scale to rate tornadoes, and the Greensburg tornado was recorded as the first EF5 tornado. This tornado however, is not the last category 5 tornado to be rated on the Fujita scale, as Canada still uses the Fujita scale, and a tornado that occurred in Manitoba in 2007 was rated an F5.

Other significant tornadoes

Map of the tornadoes that hit near Oklahoma City.

In addition to the devastating F5 tornado that hit the southern suburbs of Oklahoma City, there were numerous other significant tornadoes in the outbreak. An F3 tornado hit the town of Stroud (in between Oklahoma City and Tulsa) on Interstate 44, destroying the Tanger Outlet Mall. The mall has not been rebuilt. ^[5]

An F4 tornado hit the town of Mulhall, north of Guthrie, destroying most of the town and even toppling the city's water tower. This wedge tornado was very wide, at times exceeding width of over a mile (1.6 km). According to storm chaser Roger Edwards, it may have been as violent if not even more than the F5 Moore/Bridge Creek tornado.^[6] A Doppler On Wheels (DOW) mobile radar observed this tornado as it crossed Mulhall. The DOW documented the largest ever observed core flow circulation with a distance of 1600 m between peak velocities on either side of the tornado, and a roughly 7 km width of peak wind gusts exceeding 43 m/s, making the Mulhall tornado the largest tornado ever measured quantitatively^[7]. The DOW measured a complex multiple vortex structure^[8] with several multiple vortices containing winds of up to 115 m/s rotating around the tornado. The 3D structure of the tornado has been analyzed in Lee and Wurman 2005^[9].

One of the final tornadoes in the outbreak almost hit the studios of ABC affiliate KTUL-TV in Tulsa, located on Lookout Mountain, a few miles west of the city itself, in the early morning hours of May 4 around 12:15 a.m. CDT. Then chief meteorologist Travis Meyer advised his co-workers to take shelter while still on the air reporting on the approaching tornado. It weakened before reaching the station.

The May 3 tornado event was part of a 3-day event that included tornadoes in the states of Kansas, Texas and Tennessee. A deadly tornado killed six people in Haysville and Wichita, Kansas, the same day. The event killed 1 person in Texas on May 4 and then killed four in Tennessee on Wednesday and Thursday^{[citation needed]}.

Damage estimates

The remains of a disintegrated mobile home in Grady County, Oklahoma from the Moore, Oklahoma F5 tornado

Note: The following was adapted from public domain, official National Weather Service web sites.

The following is a list of the number of homes and businesses damaged by the tornadoes in the outbreak:

• Includes 53 stores at the Tanger Outlet Center in Stroud.

Source: National Weather Service Norman, OK Forecast Office.

See also

• List of North American tornadoes and tornado outbreaks
• Climate of Oklahoma City
• Ultimate Tornado (documentary)

References

External links

• May 3, 1999 tornado activity overlaid on a Google Map Tornado History Project
• The Great Plains Tornado Outbreak of May 3, 1999 (National Weather Service, Norman, Oklahoma)
• The 3 May 1999 Oklahoma Tornadoes (David Schultz, CIMMS)
• Google Maps' location of Stroud, Oklahoma, with the bulldozed lot of the former Tanger Outlet Mall in the upper left of the screen, just north of Interstate 44
• May 3 Oklahoma Tornado Special video section from KOCO-TV