A dry line (or dew point front) is a surface meteorological boundary separating a warm, dry air mass from a warm, moist air mass. It is not a classical thermal front (both masses may have similar temperatures), but rather a sharp humidity gradient: on one side, the dew point may be 5–10 °C and on the other 20–25 °C, with the transition occurring over just a few kilometres. The dry line is a key concept in severe weather meteorology because it acts as a powerful convective trigger mechanism. The dry air mass is less dense than the moist one (at equal temperature), so the dry line generates convergence and forced uplift along its trace. When this uplift releases existing instability (high CAPE), severe thunderstorms develop, including supercells and tornadoes. Although the concept was developed for the U.S. Great Plains (where the western Texas–Oklahoma dry line is the world's greatest tornado generator), analogous phenomena occur in other regions. In the Iberian Peninsula, the interaction between warm, dry Saharan air and moist Mediterranean air masses generates humidity gradients that can function as dry lines, contributing to the formation of the most severe storms along the Spanish Mediterranean coast.