The dryline is a boundary that separates tropical moist air from tropical dry air. A dryline is located by the distinct dewpoint gradient and wind shift that occurs at its leading boundary. The dryline tends to be most discernible in the spring and often traverses across Oklahoma and Texas. The dryline has a few distinct characteristics that make it different from a front. A dryline moves east during the day and then retreats back west at night. Typical fronts tend to move in one direction and thus do not retreat. The forward motion of a dryline occurs due to the mixing out of shallow moist air near the dryline boundary. Daytime heating initiates the mixing out of moist air along the dryline boundary. Since there is no daytime heating at night, the moist air ahead of the dryline undercuts the dry air and thus the dryline boundary retreats back west. Unlike a front which tends to have a strong density gradient, the density gradient is not as strong along a dryline. Hot and dry air has a similar density to warm and moist air. The difference in density between warm and cold air is much more pronounced, such as along a cold front. A dryline is similar to a front in that it can generated uplift along its boundary. The amount of convergence along the dryline boundary will determine the amount of uplift. In a situation is which there is strong west winds behind the dryline and strong southeast winds ahead of the dryline, the convergence along the dryline will be significant. |