WxAlerts is not affiliated with the National Weather Service. This training is informational and does not confer NWS Trained Spotter status. Official SKYWARN certification is issued by your local NWS forecast office.

Module 06

Flash flooding

The hazard that kills more people in an average year than tornadoes, and the one a spotter is least trained to describe. Seven lessons on what the words mean, what makes the rain sit still, why the same rainfall floods five regions five different ways, and what you can actually measure from a roadside.

Start lesson 01

Lessons7

Reading timeabout 3 hrs

Objectives30

The lessons

Take them in order, or don't

01What the words meanFlash flood, flood, coastal flood, debris flow. Four separate events with four separate definitions, quoted rather than summarized.Flood detailThe four events the words "flash flood" get used for, which is the difference between a report that files itself and one a forecaster has to interpret.25 min 02Why the rain stops movingRate times duration. The ingredients that set the rate, the configurations that stretch the duration, and why the storm that floods you is often the quiet one.Flood detailHeavy rain causes flooding. This lesson asks which storms drop the same rain on the same square mile for three hours, which is a different and more useful question.30 min 03Flooding is localThe same rainfall floods five places five different ways. Which one you live in decides what to watch, what to expect, and which rules of thumb will mislead you.Flood detailThe catchment decides everything. This lesson gives you five very different answers to compare your own ground against.25 min 04Why floods killThe numbers, where they come from, why they disagree with each other, and the three sentences of NWS wording worth memorising exactly.Flood detailThe research behind Turn Around Don't Drown, including which part of the famous statistic comes from which paper.25 min 05What you can actually observeDepth against a curb and a tire, flowing against ponded, a rain gauge read to hundredths, and the difference between a flooded street and a flash flood.Flood detailEvery other module teaches you to estimate one number. This teaches you which four things to say, in what order, and which of them a forecaster can act on without asking you a follow-up question.30 min 06What the radar thinks it sawQPE, flash flood guidance, recurrence intervals and FLASH. What they measure, what they do not, and why the heaviest rainfall is the kind the radar estimates worst. Which is biased low by design.Flood detailThe products a forecaster is looking at while you are on the phone, and the four documented ways each of them is wrong.30 min 07Two floods, and how this platform checks yoursTwo documented events with public data, then the reason a flood report gets a wider window and a longer memory than every other report here.Flood detailThe lesson that explains why the cross-validation rules you learned for hail and wind are the wrong rules for this hazard, and what replaces them.20 min

← All modules About the certification