The Dryline

Especially in the springtime, it's common for a well-developed "dryline" to be found in West Texas. Similar to a front, the dryline is a discontinuity that separates the hot, dry (continental Tropical; cT) air of the Desert Southwest and Mexican Plateau from the warm, moist (maritime Tropical; mT) air that flows off of the Gulf of Mexico. Typically the sudden transition occurs in the vicinity of the 50°F isodrosotherm (line of constant dewpoint temperature). Whether it stays quasistationary or progresses eastward in advance of a low pressure system and cold front, the dryline holds special interest for tornado chasers and other people interested in severe storms since the area northeast of the dryline is often very favorable for initiation of severe convective storms. More than any other atmospheric feature, this is responsible for the existence of "Tornado Alley" in North Texas and central Oklahoma. The presence of dry air contributes to the generally greater visibility of tornadoes compared to tornadoes in the eastern U.S.

This afternoon there is a well-defined dryline extending as far north as western Kansas, with dewpoints in the mT air mass typically between 65-70°F and dewpoints of 10-40°F in most of the cT air mass. Although temperatures to the west of the dryline are generally warmer in the 20 Z observations, this is primarily a reflection of a larger diurnal cycle of temperature in the drier air. In early morning, the temperature gradient will often be reversed from the afternoon pattern. The dewpoint discontinuity is often maintained and strengthened by converging surface winds within a weak lee/thermal trough. When a dryline intersects a cold front, the point where they meet is commonly referred to as the triple point.