Over the past 24 hours, a band of heavy rain fell over parts of central Mississippi into central portions of Alabama. While this band was narrow from a basin perspective–it did produce a streak of 2 inches of rain (green) with a smaller area of 2.5 to 3 inches near and east of Birmingham (yellow).
Another round of strong thunderstorms will push across this area through the nightime hours producing more heavy rainfall. While the individual storms indicate minimal training, and are scattered in coverage, they are producing pockets of heavy rainfall. Hourly rainfall amounts in the strongest storms are in the 1.0 – 1.3 inch range.
Due to the recent heavy rain, 3-hour significant runoff thresholds are around 1.6 inches overcentral Alabama, and around 2 inches over central Mississippi.
Short-term models indicate that these storms will move into central Alabama producing an average of 1 inch of rain with sisolated areas receiving 2 inches. Storms will decrease in intensity after midnight. While basin-average rainfall will not likely exceed runoff thresholds – portions of basins could exceed these thresholds by 0.50 or so. Local spots could exceed runoff values even more.
Thus, runoff could be enhanced overnight into Sunday morning over central sections of Mississippi and Alabama. The area most prone to enhanced runoff will extend 40 miles either side of a line from Columbus Mississippi, to Birmingham, to Rome Georgia. While this event is not expected to produce main steam river flooding (with isolated exceptions) it could produce a period of enhanced runoff which could result in within-bank river rises. Also, from a local perspective – flash flooding, urban flooding, enhanced local runoff could also be a concern.