The annual Southwest Monsoon, which develops during the summer months, results from low pressure over the northern Baja and high pressure over the Southern Plains; these atmospheric conditions combine to induce moisture flow from the Sea of Cortez and the western Gulf of Mexico into the Four Corners region and northward along the Front Range.
Over the past few days, a similar phenomenon has occurred further east, bringing heavy rains to eastern New Mexico and West Texas and feeding thunderstorms as far north as Colorado and Wyoming. An upper level low over the Desert Southwest and high pressure over the Southeastern U.S. have funneled moisture into the Southern Plains; this atmospheric "squeeze play" results from a counterclockwise flow around the low pressure and clockwise winds along the outer rim of the high pressure dome.
While the annual Southwest Monsoon generally waxes and wanes from June through August, the current moisture plume over the Southern Plains will likely break down within a few days; indeed, the core of the moisture appears to be moving eastward today and is now centered over the Texas-Oklahoma line. Then again, if the high pressure dome over the Southeast refuses to budge (or even expands westward), heavy rains may persist over and near the Texas Panhandle, bringing floods to a drought-plagued landscape.
