The National Weather Service in Mobile released its look at how the massive rain event of April 29-30 unfolded:

The storm developed ahead of a slow moving cold front  associated with a powerful low pressure system in the Plains, on Tuesday evening over portions of coastal Alabama and the western Panhandle.

“The widespread flooding produced sinkholes (some very large and deep), cut roads in half and necessitated human water rescues (one confirmed fatality),” the forecast reads.

The storms also came during a time when rainfall totals for the past two weeks and 30 days prior were 200 to 600 percent of normal, the release states.

“Many folks throughout the area have compared this event to the extreme flooding impacts caused by Hurricane Danny (1997),” it continues.

There were two predominant rounds of storms, the first occurred Monday night (28 April) and into the early morning hours when significant flash flooding occurred over coastal Alabama and the western Panhandle. Some 3-8” occurred in association with the first event ending 7 a.m. on April 29.

The second and more significant event occurred during the evening hours of 29 April. In that  group of storms, some 10-15” fell in an estimated nine hours and caused “disastrous flooding” throughout the area.

 Weather Service reporting sites at the airports in Mobile and Pensacola received some record rainfall. Mobile saw 11.24" during the calendar day; the third greatest total on record. Data there goes back to 1871, the weather service says.

Pensacola airport saw at least 11.13"; some data was lost during an hourlong power outage between 10 and 11 p.m., so actual amounts would have been higher.

“As it stands without the extra rainfall, this is their fourth greatest calendar day total on record. PNS rainfall data goes back to 1879.”

“Of interest in the PNS total is the 5.68" that fell in 1 hour between 02Z-03Z.” The NOAA HDSC Precipitation Frequency map shows this to be a 1 in 200 year to 1 in 500 year one hourly amount.

The 24-hour amount is about a 1 in 25 year event, as is the total for Mobile.

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