You can click on either image for much larger versions on NASA's website.
Jeff Masters of Wunder Blog explains why this historic weather event shouldn't be ignored:
Last week's storm system, in combination with heavy rains earlier this month and over past 24 hours, pushed the Ohio River at Cairo, Illinois to 60.6 feet at 1am CDT May 1. This is the highest flood in history, besting the 59.5' mark of 1937 [sic]. Additional heavy rains of 2 - 4 inches are expected over the next five days, and the river is not expected to crest until Wednesday, at a height of 61.5 feet. As the record flood waters from the Ohio River pour into the Mississippi and are joined by melt water from the this winter's record snow pack over the Upper Mississippi, all-time flood heights are likely to be exceeded at many points along a 400-mile stretch of the Mississippi below its confluence with the Ohio.
Over the next couple of weeks, this historic surge will move down the Mississippi. Officials are warning that many cities and towns along the river will see record high flood waters, potentially surpassing levels reached during the great 1927 flood, and far exceeding those reached in the 1993 Mississippi Flood that so many of us remember from our youth.
We will continue to monitor the situation, and we hope that the slow moving nature of this potential disaster gives vulnerable parties time to prepare as best they can.