It is the NOAA's way of spelling "trough". It is a low pressure ridge in the upper atmosphere which (as low pressure does) "sucks air upward" and thus causes lifting of air. If the air is moist (in the south by the gulf), that moisture condenses quickly into visible vapor and as it is lifted even higher, it cools to the point of forming water droplets that cannot be suspended in the atmosphere any longer, at which point gravity wins and rain starts. With the fast lifting and rain falling, there is plenty of static electricity buildup and a storm is born.what is "trof" ?