What is a dry line?

Dry lines are important in severe weather forecasting because they can act like a front even though temperature differences may be small. On one side, warm humid air may be flowing north from the Gulf of Mexico; on the other, hot dry air may be moving in from desert regions. The sharp contrast in moisture helps air rise, which can create thunderstorms and sometimes tornado-producing storms. Meteorologists watch dry lines closely because they often mark the place where weather changes dramatically over just a few kilometres.