Graduation

LESSON 10

By the end of this lesson

You will have a repeatable routine that links the previous lessons together, and a clear sense of what radar can and cannot tell you.

The routine

Twenty seconds, once it is habit. It is see, suspect, verify, at storm scale.

SEE

Start on the mosaic, then pick a tower. Find the storm on the regional map, then switch to a single radar site near it. Everything below assumes you are on one site. Two Pictures.
Base reflectivity, lowest tilt. Where is the heaviest precipitation and which way is it heading. Anything over 60 dBZ means hail. Intensity.
Look at the edges before the numbers. Sharp gradients mean strong updrafts, soft gradients mean weakening. Shape.
Name the shape. Scattered, cluster, line, or isolated. Isolated with clear air around it is the one that matters. Shape.
Loop four frames minimum. Is the system going where its cells are going. Is anything deviating right of the pack. Motion.

SUSPECT

Switch to velocity. Ignore the big smooth fields. Hunt for tight green touching tight red. Green and Red.
If you find a couplet, run the test. Side by side means spinning. One behind the other means spreading. Green and Red.
If it is moving fast toward or away from you, check storm relative velocity. Then switch back before you judge any wind speed. Green and Red.

VERIFY

If your app has it, check CC. Smooth and bright is weather. Mottled and dark is either not weather or something violent. When Radar Lies.
Sanity check it. How far from the radar. Does it persist across scans. Does the storm structure justify what you think you are seeing. Pull in a layer or a tool if you have one: ground temperature, lightning, the probe, whatever checks your read against something else. When Radar Lies.

If you only keep one habit

Loop it. Almost every artifact disappears when you look at four frames instead of one, and almost every real feature survives. It is the highest value habit in radar reading and it costs nothing.

Watch versus warning

These get used interchangeably in conversation and they mean genuinely different things.

	Watch	Warning
Means	Conditions are favorable	It is happening or about to
Covers	A large area, often many counties	A small polygon, often one storm
Lasts	Hours	Usually under an hour
Do	Stay aware, make a plan	Act on the plan now

A watch means the ingredients are on the counter. A warning means something is in the oven.

A tornado warning polygon is a human decision. A forecaster looked at the same things you have now learned to look at, plus environmental data and reports from people on the ground, and decided. That is worth respecting precisely because it is a judgment call made under time pressure with incomplete information.

What radar cannot do

Radar is good at Radar cannot

✓Locating and tracking precipitation

✕Tell you hail size, only that hail is likely

✓Detecting rotation aloft

✕Confirm a tornado is on the ground, except via debris

✓Showing intensity and trend

✕See below the beam, which at range is most of the lower atmosphere

✓Telling precipitation from birds, bugs and terrain

✕Measure actual surface wind

✓Watching everywhere at once

✕See through heavy precipitation, or behind terrain

Every item in that right hand column is filled by a person standing outside looking at the sky and reporting what they see. That is what SKYWARN spotters do, and it is why the training exists.

The line

Knowing how to read radar should make you take warnings more seriously, not less. The most dangerous person in a storm is the one who has learned just enough to think they can second guess a warning.

This course may have taught you a skill. It was never a weather service. When there is weather where you are, the National Weather Service and your local emergency officials are who you listen to.

The final exam

Two halves, only one graded. First, open the Live radar and work through the see, suspect, verify routine above, with Earl walking you through it one step at a time. It is here to turn the routine into a habit. Then ten final exam questions drawn from across the course, and that half is what counts toward your grade and certificate.

The final exam

A cell is isolated, has a very tight reflectivity gradient, and over the last five frames has angled noticeably right of every other storm around it. What is the most likely explanation?
It is organizing. Right deviation happens because a rotating updraft in sheared flow gets reinforced on its right side, and it often shows before a hook does.
You are looking at composite reflectivity and see a 65 dBZ core. Someone standing underneath reports light rain. Who is wrong?
Neither. Composite is a legitimate measurement of the whole column, and it regularly shows intensity that is not reaching anybody. Base reflectivity at the lowest tilt is the product that tries to answer a question about the ground.
Drawing a radial from the radar through a couplet, the beam meets intense inbound first and then intense outbound further out. What is it?
Divergence, which at low levels is a downburst. One behind the other along the radial means spreading or squeezing, and inbound first means the air is moving apart.
Which of these should make you MORE suspicious of a storm rather than less?
Distance. At 110 miles the beam is roughly two miles up and wide enough to average a tornadic circulation into nothing. Absence of a signature at range is not evidence of absence.
Intense green sits directly against intense red, with none of the middle colors between them and no gray zero line. It was not there on the previous scan. What do you do?
Treat it as a fold and wait. Real transitions pass through the intermediate colors and through zero, and real circulations persist. Something that jumps the whole scale and appears for one scan is almost always the radar wrapping around.
What is the single most valuable habit in reading radar?
Loop it. Nearly every artifact reveals itself across four frames and nearly every real feature survives. It costs nothing and it catches more mistakes than any other single habit.
A tornado-warned cell shows a tight couplet on velocity. On correlation coefficient, there is a small area of notably low, choppy values sitting right at the couplet. What does that most likely indicate?
Debris. Low, choppy CC exactly where reflectivity and velocity already agree on rotation is the classic debris signature: non-precipitation targets like tree limbs and roofing tumbling in the air, which do not scatter as uniformly as raindrops.
A narrow band of heavy snow is running roughly parallel to a steady surface wind. What should you expect if that wind shifts twenty degrees?
Lake-effect bands line up with the low-level wind, so a real shift in wind direction swings the band toward a different downwind area, which is why lake-effect snow forecasts can change so much run to run.
A hurricane is moving north at 15 mph with sustained rotational winds of about 100 mph throughout the eyewall. Which side of the storm, relative to its motion, has the strongest winds?
The right side, relative to motion. Forward motion adds onto the rotational winds there; on the left the two partly cancel. Same rotation, an uneven total wind field.
A supercell 95 miles from one radar shows a strong, tight velocity couplet on the lowest tilt. The same storm, at the same moment, looks faint and disorganized on a second radar sitting 30 miles from it. What is the most reasonable conclusion?
Velocity only measures motion straight toward or away from a given radar. The same circulation can read strong from one site and faint from another purely because of the angle each radar views it from, not because the storm actually changed. Check the other site before doubting a couplet that looked convincing.

Radar School

Radar Reader Certificate

Awarded on completion of Radar School

Type your name. It stays on this device and is sent nowhere.

Pass the quiz above and the certificate is yours. Eight of ten earns it.

You made it.

Nine lessons ago, radar was a screen full of colors. Now you can look at that same screen and see structure, motion, rotation, and the places where radar can fool you.

You do not know everything about radar. Nobody finishes one course and does. But you know how to read the picture, ask the next question, and verify what you think you see.

That is what this certificate is for.

Where to go from here

SKYWARN spotter training. Free, run by your local National Weather Service office, a couple of hours. It is the natural next step and it puts you in the reporting network.
UCAR MetEd. Free registration, and their radar meteorology coursework is genuinely excellent. It is written for aspiring meteorologists and it goes much deeper than this. If this course felt too shallow, that is where to go.
Practice on live ones. Earl is a character from RadarWrangler, a storm chasing game built on live NEXRAD data. Every round comes down to the thing these ten lessons were about: read the radar, call where the storm is heading, find out if you were right. Collect storms in each state and complete daily missions to keep your radar reading skills sharp. Keep chasing →