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 09

Radar basics for spotters

What the radar is actually measuring, how late it is, and the three things it cannot tell you no matter how good the app is. Ten lessons that end where they should: with what a trained spotter must never report from a screen.

Start lesson 01

Lessons10

Reading timeabout 4.5 hrs

Objectives40

The lessons

Take them in order, or don't

01What the radar actually doesA network of about 160 radars run by three agencies, each one listening far more than it talks, and each measuring two things that are not what you think they are.Radar detailMost spotter courses start at the picture. This starts one step back, at what the machine physically measures, because every limitation in the next nine lessons follows from it.25 min 02The beam, the curve and the holesWhy the radar sees higher and coarser the further out it looks, what sits directly overhead that it cannot see at all, and how to spot an echo that is not weather.Radar detailModule 1 told you the beam climbs with range. This is the rest of the geometry: the hole above the radar, the holes between radars, and the four ways the picture lies to you.30 min 03How old is that pictureWhat a volume scan is, what the low-level supplementary cuts buy you, and the arithmetic that converts data age into distance on the ground.Radar detailThe lesson that turns a screen into a safety calculation. Everybody knows radar is not live. Almost nobody has worked out what that means in miles.25 min 04What a dBZ isA logarithmic scale, a conversion that is an assumption rather than a measurement, and the difference between the two reflectivity products your app offers.Radar detailThe color scale everybody reads and almost nobody can define. Ten minutes here fixes several misconceptions that persist for years.25 min 05Shapes worth knowingHook echo, inflow notch, weak echo region, three-body scatter spike, bow echo and debris ball. Six shapes, and six limits on what they mean.Radar detailThe named signatures, with the thing most courses leave out: what each one does and does not license you to say.30 min 06Velocity, and what it cannot seeRadar measures motion along the beam and nothing else. Everything confusing about the velocity display follows from that one sentence.Radar detailThe product people misread most confidently. Two colors, one restriction, and a great many wrong conclusions drawn from them every severe weather season.30 min 07Dual-pol, and confirming debrisThree new fields, one of which answers a question the old radar could not: is what I am looking at even made of water?Radar detailThe upgrade that changed what radar can say, taught as what it added rather than as a list of Greek letters.30 min 08Products built from many radarsOne grid built from the whole network, updating every couple of minutes, and four derived products that are estimates rather than observations.Radar detailThe layer above the raw radar, where most of the numbers people quote actually come from, with the uncertainty that gets stripped off when they are quoted.25 min 09What not to report from a screenRadar is for knowing where to be and what is coming. It is not a source of observations, and a report sourced from it is not a spotter report.Radar detailThe lesson the whole module was built to earn. Eight lessons of what radar can do, and then the short list of things it cannot, which is the part that governs what you are allowed to say.25 min 10Six events, and what radar showedSix well-documented events from six parts of the country, each illustrating one limitation this module has spent nine lessons describing.Radar detailEverything in this module applied to events whose data is public, chosen so that each one breaks a different assumption.30 min

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