News stories about violent thunderstorms will often (maybe usually) contain a sentence to the effect of, "it struck without warning." This is a statement that makes meteorologists bristle, because when exceptionally violent weather strikes, we are almost always quite busy broadcasting about the very storm that struck "without warning." To be sure, the very nature of violent thunderstorms is that they are rather small in scale and develop rather quickly. It is simply not possible to predict very far in advance the precice location where one will strike.
Instead, we offer a generalized forecast of severe storm potential a day or two in advance, some sort of severe storm watch a few hours in advance, and usually a severe thunderstorm or tornado warning is in place minutes before severe weather happens. When the storm actually occurs, it will happen quickly. However, it is not at all common for severe thunderstorms to hit entirely without some advance information from broadcast meteorologists.