A 500-year rain, by definition, has a 0.2 percent chance of occurring in any given year; it does not mean that occurrences are 500 years apart. How much water would that take? From the Sunday Oklahoman:
For Oklahoma City, the following rainfall amounts would be considered 500-year rainfall events, according to Gary McManus, state climatologist, who referenced a report prepared by the U.S. Geological Survey:
- 2.6 inches of rain in 15 minutes.
- 3.7 inches of rain in 30 minutes.
- 5.2 inches of rain in one hour.
- 6.8 inches of rain in two hours.
- 7.6 inches of rain in three hours.
- 8.4 inches of rain in six hours.
- 9.6 inches of rain in 12 hours.
- 12.5 inches of rain in 24 hours.
- 14.8 inches of rain in three days.
- 15.5 inches of rain in seven days.
I’m pretty sure I’ve seen the first three of these, and maybe more, during the 40+ years I’ve lived here. Example:
11.26 inches recorded on 6-14-2010 at a station 6.1 miles north of downtown Oklahoma City.
That’s almost certainly the OKC North Mesonet station. The “official” total for that day was 7.62 inches at Will Rogers World Airport, where the National Weather Service takes readings.
I think we can kiss that record goodbye. One of the Mesonet stations in town has already made it up to 8, the others aren’t far behind, and it’s still raining. The office ranges from 0.5 to 4.5 inches of water inside. Jesus Christ could walk through the parking lot, but He’s just about the only one.
On the upside, this served as a test for my new $10,000 roof, installed a few days before.