Tornadoes can happen all months of the year and in pretty much any location. They tend to happen more often in some times (Spring and Summer) and some locations (the US midwest, for one). Oklahoma has already had tornado fatalities this year.
The weather folks make a big deal of Watches and Warnings. Not just for tornadoes, but for other severe weather. And I suspect I am not alone in occasionally getting them confused. Does watch mean "Watch out, it might be happening." or "Watch out, it is happening."? Is a warning "This could be dangerous." or "This is dangerous."? Even after hearing the explanations that are supposed to clarify, the two definitions come at about the same time and are still apt to get confused.
There is a simple way to distinguish these two things. One is grammatically incorrect, but I think that doesn't matter too much in this case.
WatCh - "C" - It could happen.
WaRning -"R" - It are happening!
ADDENDUM: Alternately, haystack suggests the more grammatically correct:
WarnIng - "I" - It is happening!