WASHINGTON —聽Not only was the flash flooding in Ellicott City deadly and damaging, it was also extremely unlikely. According to the National Weather Service office in Sterling, Virginia, the precipitation amounts that occurred have a 鈥渓ess than one tenth of 1 percent (less than 0.1 percent) chance of occurring in any year.”
The following is a table of rainfall amounts occurring within specific time frames of the worst of the thunderstorms. Note that this particular rain gauge reports in increments of 0.04 inch. These are incredible rainfall rates and simply overwhelmed the storm drainage infrastructure.
DURATION聽聽聽 AMOUNT聽聽 TIMEFRAME
聽 聽 聽—————————————-
1 minute聽聽聽 0.20聽聽聽聽 7:51pm-7:52pm
5 minutes聽聽 0.80聽聽聽聽 7:50pm-7:55pm
10 minutes聽 1.44聽聽聽聽 7:50pm-8:00pm
15 minutes聽 2.04聽聽聽聽 7:46pm-8:01pm
20 minutes聽 2.48聽聽聽聽 7:44pm-8:04pm
30 minutes聽 3.16聽聽聽聽 7:36pm-8:06pm
60 minutes聽 4.56聽聽聽聽 7:30pm-8:30pm
90 minutes聽 5.52聽聽聽聽 7:00pm-8:30pm
2 hours聽聽聽聽 5.92聽聽聽聽 6:45pm-8:45pm
鈥淒uration鈥� refers to elapsed time after the rain started. The 鈥渁mount鈥� is a running total, not total within the specific time frame.
The storm total for Ellicott City was recorded as 6.50 inches.
This data is preliminary and is subject to correction.
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