Question: When was the most rainfall for Oklahoma's largest city?

full_context: Document 1: Oklahoma City: Oklahoma City is on the I-35 Corridor and is one of the primary travel corridors into neighboring Texas and Mexico. Located in the Frontier Country region of the state, the city's northeast section lies in an ecological region known as the Cross Timbers. The city was founded during the Land Run of 1889, and grew to a population of over 10,000 within hours of its founding. The city was the scene of the April 19, 1995 bombing of the Alfred P. Murrah Federal Building, in which 168 people died. It was the deadliest terror attack in the history of the United States until the attacks of September 11, 2001, and remains the deadliest act of domestic terrorism in U.S. history.
Document 2: Oklahoma: Because of Oklahoma's position between zones of differing prevailing temperature and winds, weather patterns within the state can vary widely over relatively short distances and can change drastically in a short time. As an example, on November 11, 1911, the temperature at Oklahoma City reached 83 °F (28 °C) in the afternoon (the record high for that date), then an Arctic cold front of unprecedented intensity slammed across the state, causing the temperature to crash 66 degrees, down to 17 °F (−8 °C) at midnight (the record low for that date); thus, both the record high and record low for November 11 were set on the same date. This type of phenomenon is also responsible for many of the tornadoes in the area, such as the 1912 Oklahoma tornado outbreak, when a warm front traveled along a stalled cold front, resulting in an average of about one tornado per hour over the course of a day.
Document 3: Oklahoma City: As of the 2010 census, there were 579,999 people, 230,233 households, and 144,120 families residing in the city. The population density was 956.4 inhabitants per square mile (321.9/km²). There were 256,930 housing units at an average density of 375.9 per square mile (145.1/km²).
Document 4: Oklahoma City: The city is roughly bisected by the North Canadian River (recently renamed the Oklahoma River inside city limits). The North Canadian once had sufficient flow to flood every year, wreaking destruction on surrounding areas, including the central business district and the original Oklahoma City Zoo. In the 1940s, a dam was built on the river to manage the flood control and reduced its level. In the 1990s, as part of the citywide revitalization project known as MAPS, the city built a series of low-water dams, returning water to the portion of the river flowing near downtown. The city has three large lakes: Lake Hefner and Lake Overholser, in the northwestern quarter of the city; and the largest, Lake Stanley Draper, in the sparsely populated far southeast portion of the city.
Document 5: Oklahoma: Oklahoma had 598 incorporated places in 2010, including four cities over 100,000 in population and 43 over 10,000. Two of the fifty largest cities in the United States are located in Oklahoma, Oklahoma City and Tulsa, and 65 percent of Oklahomans live within their metropolitan areas, or spheres of economic and social influence defined by the United States Census Bureau as a metropolitan statistical area. Oklahoma City, the state's capital and largest city, had the largest metropolitan area in the state in 2010, with 1,252,987 people, and the metropolitan area of Tulsa had 937,478 residents. Between 2000 and 2010, the cities that led the state in population growth were Blanchard (172.4%), Elgin (78.2%), Jenks (77.0%), Piedmont (56.7%), Bixby (56.6%), and Owasso (56.3%).
Document 6: Oklahoma: In descending order of population, Oklahoma's largest cities in 2010 were: Oklahoma City (579,999, +14.6%), Tulsa (391,906, −0.3%), Norman (110,925, +15.9%), Broken Arrow (98,850, +32.0%), Lawton (96,867, +4.4%), Edmond (81,405, +19.2%), Moore (55,081, +33.9%), Midwest City (54,371, +0.5%), Enid (49,379, +5.0%), and Stillwater (45,688, +17.0%). Of the state's ten largest cities, three are outside the metropolitan areas of Oklahoma City and Tulsa, and only Lawton has a metropolitan statistical area of its own as designated by the United States Census Bureau, though the metropolitan statistical area of Fort Smith, Arkansas extends into the state.
Document 7: United Kingdom weather records: Duration Level Location Date Highest 5 - min total Approx. 32 mm Preston, Lancashire 10 August 1893 Highest 30 - min total 80 mm Eskdalemuir, Dumfries and Galloway 26 June 1953 Highest 60 - min total 92 mm Maidenhead, Berkshire 12 July 1901 Highest 90 - min total 117 mm Dunsop Valley, Lancashire 8 August 1967 Highest 120 - min total 155 mm Hewenden Reservoir, West Yorkshire 11 June 1956 Highest 155 - min total 169 mm Hampstead, London 14 August 1975 Highest 180 - min total 178 mm Horncastle, Lincolnshire 7 October 1960 Highest 24 - hour total (1800 - 1800) 341.4 mm Honister Pass, Cumbria 5 December 2015 Highest 24 - hour total (0900 - 0900) 279 mm Martinstown, Dorset 18 July 1955 Highest 48 - hour total (0900 - 0900) 405 mm Thirlmere, Cumbria 4 to 5 December 2015 Highest 72 - hour total (0900 - 0900) 456.4 mm Seathwaite, Cumbria 17 to 19 November 2009 Highest 96 - hour total (0900 - 0900) 495 mm Seathwaite, Cumbria 16 to 19 November 2009 Highest Monthly Total 1396.4 mm Crib Goch, Snowdon 1 to 31 December 2015
Document 8: Oklahoma City: Oklahoma City has a very active severe weather season from March through June, especially during April and May. Being in the center of what is colloquially referred to as Tornado Alley, it is prone to especially frequent and severe tornadoes, as well as very severe hailstorms and occasional derechoes. Tornadoes have occurred in every month of the year and a secondary smaller peak also occurs during autumn, especially October. The Oklahoma City metropolitan area is one of the most tornado-prone major cities in the world, with about 150 tornadoes striking within the city limits since 1890. Since the time weather records have been kept, Oklahoma City has been struck by thirteen violent tornadoes, eleven F/EF4s and two F/EF5. On May 3, 1999 parts of southern Oklahoma City and nearby suburban communities suffered from one of the most powerful tornadoes on record, an F5 on the Fujita scale, with wind speeds estimated by radar at 318 mph (510 km/h). On May 20, 2013, far southwest Oklahoma City, along with Newcastle and Moore, was hit again by a EF5 tornado; it was 0.5 to 1.3 miles (0.80 to 2.09 km) wide and killed 23 people. Less than two weeks later, on May 31, another outbreak affected the Oklahoma City area, including an EF1 and an EF0 within the city and a tornado several miles west of the city that was 2.6 miles (4.2 km) in width, the widest tornado ever recorded.
Document 9: Oklahoma City: Oklahoma City is the capital and largest city of the state of Oklahoma. The county seat of Oklahoma County, the city ranks 27th among United States cities in population. The population grew following the 2010 Census, with the population estimated to have increased to 620,602 as of July 2014. As of 2014, the Oklahoma City metropolitan area had a population of 1,322,429, and the Oklahoma City-Shawnee Combined Statistical Area had a population of 1,459,758 (Chamber of Commerce) residents, making it Oklahoma's largest metropolitan area. Oklahoma City's city limits extend into Canadian, Cleveland, and Pottawatomie counties, though much of those areas outside of the core Oklahoma County area are suburban or rural (watershed). The city ranks as the eighth-largest city in the United States by land area (including consolidated city-counties; it is the largest city in the United States by land area whose government is not consolidated with that of a county or borough).
Document 10: Oklahoma City: Oklahoma City has experienced significant population increases since the late 1990s. In May 2014, the U.S. Census announced Oklahoma City had an estimated population of 620,602 in 2014 and that it had grown 5.3 percent between April 2010 and June 2013. Since the official Census in 2000, Oklahoma City had grown 21 percent (a 114,470 raw increase) according to the Bureau estimates. The 2014 estimate of 620,602 is the largest population Oklahoma City has ever recorded. It is the first city in the state to record a population greater than 600,000 residents and the largest municipal population of the Great Plains region (OK, KS, NE, SD, ND).
Document 11: Oklahoma City: While not in Oklahoma City proper, other large employers within the MSA region include: Tinker Air Force Base (27,000); University of Oklahoma (11,900); University of Central Oklahoma (2,900); and Norman Regional Hospital (2,800).
Document 12: Broken Arrow, Oklahoma: Broken Arrow is a city located in the northeastern part of the U.S. state of Oklahoma, primarily in Tulsa County but also with a section of the city in western Wagoner County. It is the largest suburb of Tulsa. According to the 2010 census, Broken Arrow has a population of 98,850 residents and is the fourth-largest city in the state. However, a July 2017, estimate reports that the population of the city is just under 112,000, making it the 280th-largest city in the United States. The city is part of the Tulsa Metropolitan Area, which has a population of 961,561 residents.
Document 13: Oklahoma: All of the state frequently experiences temperatures above 100 °F (38 °C) or below 0 °F (−18 °C), though below-zero temperatures are rare in south-central and southeastern Oklahoma. Snowfall ranges from an average of less than 4 inches (10 cm) in the south to just over 20 inches (51 cm) on the border of Colorado in the panhandle. The state is home to the Storm Prediction Center, the National Severe Storms Laboratory, and the Warning Decision Training Branch, all part of the National Weather Service and located in Norman. Oklahoma's highest recorded temperature of 120 °F (49 °C) was recorded at Tipton on June 27, 1994 and the lowest recorded temperature of −31 °F (−35 °C) was recorded at Nowata on February 10, 2011.
Document 14: Oklahoma City: Oklahoma City is the principal city of the eight-county Oklahoma City Metropolitan Statistical Area in Central Oklahoma and is the state's largest urbanized area. Based on population rank, the metropolitan area was the 42nd largest in the nation as of 2012.
Document 15: Oklahoma City: With 19.48 inches of rainfall, May 2015 was by far Oklahoma City's record-wettest month since record keeping began in 1890. Across Oklahoma and Texas generally, there was record flooding in the latter part of the month
ground_truth: May 2015
sub_queries: What is Oklahoma's largest city? Answer: Oklahoma City
When was the most rainfall for Oklahoma City ? Answer: May 2015