1000 Year Flood in TN

This report from NOAA on the recent flooding in TN is absolutely amazing. 

Flooding Facts:

• Fifteen (15) observation sites had rainfall measurements exceeding the maximum observed rainfall associated with Hurricane Katrina landfall.
• The two day rainfall of 13.57 inches at Nashville International Airport shattered the monthly rainfall record for May which was 11.04 inches.
• The rainiest month in Nashville is 13.92 inches in January 1950.
• Nashville International Airport experienced its 1st and 3rd rainiest days on back to back days.
• The heaviest rainfall occurred in a swath across Davidson, Williamson, Dickson, Hickman, Benton, Perry, and Humphreys Counties.  An average of 14 to 15 inches of rain fell equivalent to 420 billion gallons of water in just two days.

What is a 100 year flood?  A 100 year flood is an event that statistically has a 1% chance of occurring in any given year. A 500 year flood has a .2% chance of occurring and a 1000 year flood has a .1% chance of occurring. 

The map below relates the amount of rainfall that fell to the chances of that amount of rain actually occurring.