When we receive a lot of heavy rain in a short period of time, flash flooding can occur. The Weather Prediction Center (WPC) releases risk levels for excessive rainfall up to five days in advance. Let's break down what these different risk levels are and what they mean.
For Day 1, 2 and 3 risks, there are four different risk levels. The first level is a low or marginal risk for flooding. You will see this as an area highlighted in green on the map. With this risk level, isolated flash flooding is possible. Any flooding is very localized, and it mainly affects areas that see rapid runoff.
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The second level is a medium or slight risk of flooding. You will see this highlighted as an area in yellow on our maps. This means that scattered flash flooding is possible. Any flooding is still mainly localized, but we can see it more spots like urban areas, small streams, etc. Some isolated spots could see significant flooding.
The third level is called a moderate risk by the WPC, but our team calls this a high risk. This is due to the higher threat for numerous flash floods. This is highlighted by an area in red on our maps. Many streams may flood and could affect larger rivers. There is also a possibility for significant floods.
The last level is called a high risk by the WPC, but our team calls this an extreme risk. This is because widespread flash flooding is possible with this risk level, and there is a more significant threat to life and property. It will show up as area of pink on the map. Even areas that do not normally flood could flood with this risk level.
Once you get to Day 4 and 5, only 3 of the 4 risk levels are used because the predictability is too low for the extreme risk level. A low risk means at least a 5% probability of the area within 25 miles of a single point could see flash flooding. This increases to 15% with a medium risk, 40% with a high risk, and 70% with an extreme risk.
Be sure to have the WRAL Weather App downloaded, so you can check any flood alerts and have push notifications sent to your phone. Always remember: Turn around, don't drown! Never try to drive through flooded roadways.