Six events, and what radar showed
Six well-documented events from six parts of the country, each illustrating one limitation this module has spent nine lessons describing.
Why these six
Each one is documented on a public NWS event page with archived data, and each one breaks a different assumption. They are spread across the country on purpose: nothing in this module is regional, and neither are its failure modes.
Bridge Creek and Moore, Oklahoma, 3 May 1999
The event that produced the highest tornado wind speed ever reliably measured: a Doppler on Wheels recorded about 301 mph, plus or minus 20, at roughly 105 feet above ground. Note the height: it took a mobile radar parked close by to measure that near the surface, and it is the sort of measurement the fixed network cannot make at all.
Tuscaloosa and Birmingham, Alabama, 27 April 2011
A violent, highly visible, well-observed EF4 during the largest outbreak in decades. Its value here is a technical accident: the Birmingham radar was still single-polarisation that day. The network-wide A 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. upgrade had begun weeks earlier and had not reached it.
Joplin, Missouri, 22 May 2011
The deadliest single US tornado since 1950, with 158 fatalities, and Hidden inside the precipitation around it. A rain-wrapped tornado breaks none of the identification rules; it just denies you the observation those rules rely on. for much of its life. The service assessment finding that lesson 3 quoted comes from here: "limited scans at lowest elevation slices during this time impacted the Weather Forecast OfficeA local National Weather Service office. It issues the warnings for its own area, and it is the office your report reaches.'s ability to ascertain the magnitude of the tornado."
Read that alongside lesson 3. It is the reason supplementary low-level scanning exists in the form it does, and it is a case where the limiting factor was not what the radar could see but how often it was looking at the part that mattered.
El Reno, Oklahoma, 31 May 2013
Module 8 lesson 1 covers this event for its safety record. Here it is the rating that matters. A mobile polarimetric radar measured winds greater than 295 mph in sub-vortices near the surface. The official rating is EF3.
The Iowa A long-lived, fast-moving windstorm produced by a line of thunderstorms, leaving damage in a swath rather than at scattered points. One of only two things that can put an area under a HIGH risk., 10 August 2020
A textbook A segment of a line of storms that has surged forward into a bow shape on radar. The apex of the bow is where the strongest straight-line winds are. with a A current of air flowing into the back of a line of storms and descending toward the leading edge. Where it reaches the ground it pushes the gust front forward, which is what makes a line bow., and the costliest thunderstorm event on record at around 11.2 billion dollars. Lesson 5's bow echo section describes what it looked like; module 2 lesson 8 has the physics.
Both appear in the public record for the same event and they are not in conflict. Module 7 lesson 3 asks you to tag your own numbers as measured or estimated for exactly this reason: the distinction survives into the archive and people reading it years later need it.
The Quad-State tornado, 10 to 11 December 2021
A long-track nocturnal tornado family that crossed several states, with the Mayfield, Kentucky damage among the worst of it. December, at night, over a long distance.
Working the archive yourself
The full-resolution radar data for every event above is public and free. Archived The full-resolution base radar data as recorded: reflectivity, velocity, spectrum width and the dual-polarisation fields at every elevation. Large, complete, and what research and the better desktop applications use. lives in the unidata-nexrad-level2 bucket on AWS, in us-east-1, readable with --no-sign-request and no account. Real-time chunks and Derived and reduced radar products generated from Level II: single tilts, algorithm output, accumulations. Smaller and quicker to distribute, and what most public-facing displays are built from. have their own buckets alongside it.
Open-source tools will read it: Py-ART, MetPy and xradar are all freely licensed and all render the fields this module has described. Local storm reports for the same events are archived by the Iowa Environmental Mesonet, so you can put the reports beside the radar and see for yourself how well they line up. That exercise teaches this module better than this module does.
For the 10 August 2020 Iowa derecho, the record contains both a 126 mph figure and a 140 mph figure. What is the relationship between them?
Module 7 asks you to tag every number in your own reports with exactly this distinction.One was measured and one was estimated from damage, and both are legitimately in the record for the same event. This is why module 7 insists you label your own numbers: the distinction has to survive into the archive for anybody reading it later to interpret it.