NOAA Storm Prediction Center (Centre- SPC) meteorologists tend to issue forecasts on a daily basis – aka convective outlooks – for organised thunderstorms over the U.S. based upon the current weather observations/forecast models.
The SPC meteorologists closely monitor areas they believe are at a higher risk for Tornadoes. If said conditions develop (that are favourable for Tornadoes), the SPC meteorologist (involved) would issue a severe Thunderstorm/Tornado watch.
Thunderstorm/Tornado watches tend to last four to six hours. Affected (local) forecast offices, emergency managers, storm spotters and the public are alerted to the likelihood of severe weather – Tornadoes.
Tornado warnings tend to be issued by the local National Weather Service forecast office when either has been seen on the ground or indicated by radar. It would be safe to say people in the affected (warning) area should seek shelter immediately.
You can find out more on Tornado forecasting here.
It’s safe to suggest that meteorologists/skywarm storm spotters have learned to identify certain thunderstorm characteristics and structure that enables the formation of a Tornado (more likely).
Some of these characteristics are visual, for example, rear-flank downdraft (RFD). Other characters are particular patterns in radar image, like TVS aka Tornadic vortex signature (TVS).
ICYDK: Skywarm Storm spotters (spotters) have been taught to identify Tornado conditions and report what they see to that National Weather Service. Spotters can be anyone from any background – however they must have taken formal storm spotter training.
Computer algorithms (detail series of instructions for carrying out an operation/problem solving) analysis Doppler radar data and displays it in a way that makes it easier for meteorologists to identify extreme (and dangerous) weather events.
It’s say to suggest that a Thunderstorm with a Tornado observed by radar has certain characteristics that meteorologists are trained to recognise them…
…We’re going to leave it there for Tornado detection! You can find out more on Tornado detection here.