Elwell: La Niña unleashes threat for flooding across Ohio Valley, Midwest

Feb 19, 2018

It is around this time of year that I must admit, I am ready to rush spring.

While I do love a good snow storm, I’m not a big fan of gray and dreary days with the landscape still being brown. But it appears we are in store for a lot more of this gloomy weather over the coming days and, perhaps, weeks.

You may remember months ago our Storm Center 7 forecast that La Niña would likely be the dominating pattern across North America this winter.

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La Niña, the direct opposite of El Niño that we experienced last winter, occurs when sea surface temperatures in the central Pacific Ocean drop to lower-than-normal levels. The typical impact across the Ohio Valley during a La Niña winter is near average temperatures but above average precipitation thanks to a more active jet stream pattern. So far, that forecast has been pretty spot on.

But now a new concern is emerging thanks to the current La Niña pattern. Over the coming days, a large area of high pressure is expected to develop just off the southeast coast of the United States.

With the clockwise flow around this high, ample moisture is expected to be pushed northward out of the Gulf of Mexico into the Ohio Valley. In fact, some of our more reliable model data suggests precipitable water levels — that’s the depth of water in a column of the atmosphere, if all the water in that column were precipitated as rain —could approach record levels in parts of the Ohio Valley over the next week to 10 days. The hope is that all that moisture won’t get “rained out.” If that were to happen, there could be a significant flooding concern.

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This is something that will have to be watched closely over the coming days, as it is this type of pattern that can lend itself to severe flooding. Heavy rain this time of year falls onto a ground that is typically already saturated from recent snowmelt and previous rain storms.

Because there is no vegetation growing, there is nothing to absorb that moisture and nothing that slows the water from rapidly moving into area rivers and streams. This can lead to even faster rises of water levels than what is typical during spring and summer rains.

The weather pattern shows numerous storm systems being pushed into the Ohio Valley as they move around high pressure locked across the southeastern U.S. This pattern will likely lead to these storms systems having plenty of moisture to work with as the move by.

It is quite possible as much as 4 inches of more of rain could fall across parts of the Miami Valley over the next five to seven days. Now is the time to make sure your basement sump pumps are working and perhaps think about a battery back-up. Just remember, floods kill more people each year than tornadoes, hurricanes or lightning, so it is something to take seriously.

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As far as if the coming rains signal an early end to winter, I wouldn’t count on it. There our several indications winter will try to fight back in early March. So, don’t get too used to temperatures near 70 degrees as typically this type of warmth doesn’t stick around until late April or May.

For now, we will just have to get use to the gray and dreary days … and you can thank La Niña for that!