HARRISBURG (WHTM) By now you’ve heard about the horrific flooding that is still ongoing in parts of Louisiana. Some isolated spots have reported as much as 30″ of rainfall while a large swath of land picked up over one foot of rain over the past few days. Four people have died and thousands of water rescues have been needed in and around Baton Rouge.
So what has caused so much rain to fall over a short time? The area has very sandy soil to start, and with a history of many tropical storms impacting the region, the ground can handle large amounts of water. But still, this system was impressive due to its lack of movement. For 36 to 48 hours, a large area of low pressure sat off the Gulf of Mexico coast, pumping tropical air and vast amounts of moisture into the region. In many ways this could be compared to a tropical storm or hurricane, but without the wind or storm surge. The position of the system allowed for deep convection (heavy downpours) to develop out over the water and then slide inland. Again, this happens often with tropical storms, but the difference here is that the system didn’t really move for an extended period of time.We have even seen a heavy stream of tropical air deliver flooding rains to our region. Remember Tropical Storm Lee and the look of the radar reaching all the way from Pennsylvania to the Gulf coast. Of course Louisiana is much closer to the Gulf and can experience exponentially more rainfall from these system.
You can see some of that convection that caused the flooding on our water vapor map from Friday night. The deep green colors indicate lots of moisture in even the upper levels of the atmosphere, and that can translate to intense rainfall rates falling to the surface of 2-3″ per hour at times.
Flood waters will continue to rise as water moves toward low lying areas and streams, creeks and rivers. In the days to come the weather pattern looks dangerous in the sense that additional heavy rain will be possible. It will likely not be as heavy as what has already fallen, but even another 5-6″ of rain will undoubtedly cause additional problems. It does not look to be until late in the week that the pattern breaks and this river of moist air tapping into the Gulf of Mexico shuts off.