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Why river flood warnings are issued, even when impacts are minimal

If you have any whether questions, don't hesitate to ask! luke.victor@kmiz.com or weather@kmiz.com

I got a question in an e-mail on Tuesday-- a viewer asked why river flood warnings get issued, and it may not come up in a news story or our weather forecasts. This viewer wondered if damaged levees were to blame. While the levees aren't in the best shape, it's actually simpler than that.

The National Weather Service and River Forecasting Center work together in monitoring impacts along rivers and streams across the United States. Each waterway has hundreds of different gauge which measure water levels and help forecast for potential/ongoing flooding conditions.

The picture below shows all gauges located in the state of Missouri.

(Interactive flood gauge map) https://water.weather.gov/ahps/region.php?state=mo

Each gauge has an established level at which flooding begins to occur. This is called the minor flood stage and impacts are low.

Below that is the action stage. This serves the same function as a "watch" for the river flood. That is to say, flooding conditions are very close to happening. Moderate and major impact flooding are what we dealt with for most of the summer as many river gauges measure water 5-15 feet above their action stages.

Below are the different stages for flooding at the Jefferson City gauge which is located near the highway 63 bridge connecting Boone and Cole counties.

Essentially what can happen is that river levels can get "stuck" in the action stage as they drain following a wet year. Any rain that falls on top can bring the river level back up, activating the warning.

Similar to a sink with a slow drain-- too much is going in, than going out keeping the flooding active-- even if impacts are low.

The flood of 2019 left Missouri River levels elevated for several months which is why it seemed like the warnings never ended, even though there were no major impacts being experienced.

Thankfully we're continuing to see water recede below flood levels as precipitation has remained below normal since November.

-Luke

Insider Blog

Luke Victor

Luke Victor gives forecasts on ABC 17 News broadcasts and reports on weather stories on air and online, giving viewers and readers a deeper look at what causes different types of weather.

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