What not to report from a screen

What radar is genuinely good for, to you

Everything in this module has a use, and the uses are mostly about where you are and what is about to arrive, which is module 8 material with better inputs.

• Knowing what is coming and roughly when, so you are in a sensible place beforehand rather than reacting.
• Choosing standoff distance, with lesson 3's latency arithmetic applied so your margin accounts for the picture being old.
• Watching your escape routes, because a second line of storms arriving behind you is visible on radar long before it is visible to you.
• Knowing which part of the storm you are looking at, so what you describe in a report is anchored to structure rather than to a direction.
• Knowing when to stop, which is the module 8 lesson 8 decision and is much better informed with radar than without.

The line

The field guide puts the same point from the other end: "Radar is an excellent tool, but it is just that: one tool among many that NWS uses." The office already has the radar. It has it at full resolution, sooner than you do, with training you do not have. What it does not have is your eyes.

Four amateur misinterpretations

1. Calling a tornado from a hook. The hook is precipitation wrapping around rotation, thousands of feet up, and most hooks produce no tornado. Lesson 5.
2. Reading gate-to-gate shearChange of wind with height, measured as the difference between the wind at the top and bottom of a layer. It is not needed to make a thunderstorm and it decides almost everything about what kind you get. at long range. At 100 km the sample volume is kilometres wide and a tight circulation is averaged away, so a convincing couplet there is either large or is not what you think. Lessons 2 and 6.
3. Treating purple as severity. On many colour scales purple is range-folded data, meaning no data. It is the absence of a measurement being read as an extreme one. Lesson 6.
4. Trusting a composite as a surface observation. It is a column maximum with the height thrown away. Lesson 4.

Apps

This course recommends no product and endorses none. What it can tell you is what to require of whichever one you use.

• A visible timestamp on every frame. Lesson 3. An app that hides the age of its data is unusable for positioning.
• Base products, not only composites. If you cannot get base reflectivityReflectivity from one elevation tilt, usually the lowest. A real slice through the atmosphere at a height that climbs with range. and base velocity, you cannot do most of this module.
• Storm-relative velocityThe velocity field with the storm motion subtracted out, leaving the circulation within the storm. Only as good as the storm motion that was assumed: a wrong motion can invent a circulation or hide one., and ideally control over the assumed storm motion.
• The dual-polA radar upgrade that sends pulses both horizontally and vertically, so the returns say something about the shape of what they hit. It is what lets radar recognise lofted debris. fields, without which lesson 7 is theory.
• Honest handling of missing data, so range foldingReturns from beyond the radar unambiguous range, assigned to the wrong distance and displayed as missing data, purple on many colour scales. Purple means no measurement, not a severe one. looks like absence rather than like a value.

Warning polygons

One last practical item. A warning polygonThe shape a warning is drawn on, replacing whole-county warnings in 2007. Being inside the shape is what matters, not which county you are in. is a forecast of where the hazard will be during the valid period, not a drawing of where it is now. It has a start and an end time, and being just outside one is not a statement that you are safe. Module 1 lesson 5 covers the anatomy of the product and module 7 lesson 5 covers how your report can change one while it is running.