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Why You Should Pay Attention to 'High Risk' Flood Forecasts

The Weather Channel logoThe Weather Channel 9/13/2021 Jonathan Erdman
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When a meteorologist mentions a "high risk" of flooding rain, chances are the flooding will be deadly and destructive, not simply a day of soaking rain.

Two-fifths of all U.S. flood deaths from 2010-2018 occurred on days with a high risk forecast, about 16 days a year, on average, according to research by Alex Lamers, a meteorologist at NOAA/WPC.

(MORE: Recent Years Show Why Houston Is Likely America's Rainfall Flooding Capital)

Put another way, 51% of "high risk" flood days had at least one flood fatality or injury, according to Lamers.

Furthermore, 86% of all flood-related damage occurs in and near these high risk areas. In 2018, property damage in high risk areas was estimated to exceed $1 billion, according to Greg Carbin, NOAA/WPC chief of forecast operations.

Lamers also found high risk flood forecasts issued one or two days ahead of the event, rather than the day of the event, have produced even more damage and fatalities.

Just as a high risk of severe thunderstorms in a severe thunderstorm outlook from NOAA's Storm Prediction Center indicates higher confidence of a major event such as a tornado outbreak, a high risk excessive rain outlook points out those scenarios that aren't your typical local flash flood event.

A more typical soaking rain may trigger minor flooding in areas that typically see runoff, such as urban, poor-drainage areas, roads and small streams. These are typically covered by "marginal" or "slight" risks in the WPC outlook.

When a high risk is issued, the WPC expects severe, widespread flash flooding, including areas that don't normally experience flash flooding.

Some of the areas that could flood during a high risk day include parts of your commute to work, a shopping center parking lot, the street outside your front door, your yard, even your basement or home. You may see areas you've never seen flood before take on water if your area is covered by a "high risk" outlook.

High risks may be issued in advance of tropical storms and hurricanes such as Harvey and Florence, with large-scale areas of heavy rain in other parts of the country or in smaller areas where terrain may play a significant role, as was the case in California in February 2019.

Some more recent flood events since 2018 covered by WPC high risk outlooks included:

-Late-May 2019 Kansas and Oklahoma flood

-Late-February 2019 Tennessee Valley flood

-Hurricane Michael's flooding rain in Virginia and North Carolina (October 2018)

-Hurricane Florence's record rain (September 2018)

What should you do if you're in a high risk for flooding rain?

Pay close attention to NWS flash flood warnings and particularly NWS flash flood emergencies, which are issued when life-threatening flooding is occurring.

Never drive through flooded roads. Roughly two-thirds of all flash flood deaths occur in vehicles swept away or submerged in floodwater.

"When you see rising water running across the road in front of you, don't become another statistic. Find a drier way," said Carbin.

Keep off bridges over fast-moving water and stay away from fast-flowing creeks or rivers.

Evacuate or move to higher ground immediately if told to do so by local emergency management.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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