When air rotates with dust or water particles it becomes electrified. This has been proven over and over again, for example, Philip Lenard Nobel Laureate from 1905 studied this phenomena extensively and the effect was named after him – the Lenard effect (also known as the spray electrification effect). This electrical charge can be measured and has been studied extensively by NASA. There is great concern about this phenomena for Martian astronauts. See the video NASA MATADOR Electrified Tornadoes
www.youtube.com.
So all rotating air, even very slow rotations of dust devils, generate electric charge. Is there always lightning? Well, there are different kinds of lightning. Most people are familiar with cloud to ground lightning which is the most powerful and causes great thunder claps. There have been many studies over the past half century showing that there isn’t always enough charge generated to create cloud to ground lightning with tornadoes – there is very little correlation between tornadoes and cloud to ground lightning. In fact some studies show that lightning holes, areas of very little cloud to ground lightning, are created when tornadoes form.
Then there is cloud to cloud lightning or intercloud or intracloud lightning. This type isn’t always visible during the day and may not generate a thunder clap. There is always some amount of detectable electrical activity present regardless of whether it is visible or not. Then there are the other forms of radiation generated by storms – gamma rays and positrons – that aren’t visible but emit detectable VLF radio signals. Tornado Alert is testing the electrical charge density in the atmosphere for tornadoes, not the discharge counts of lightning.