Yesterday afternoon, a low pressure center, associated with a cold front, sat over southeastern Colorado. Its counterclockwise winds, dragging in moisture from the High Plains, produced "upslope" conditions along the Front Range, dumping up to a foot of snow in Metro Denver.
Meanwhile, an "upper level low," which formed over the Gulf of Mexico, drifted northward along the Alabama-Georgia line, bringing heavy rains to this drought-plagued region. Initially, since high pressure was parked over the eastern U.S., this disturbance was forecast to move eastward, across northern Florida. Fortunately, this "blocking high" retreated to the north and the isolated low, not associated with a front, was able to pull Gulf moisture into the drought zone. This morning, the low had moved into the mid-Atlantic region, producing beneficial rains across North Carolina and Virginia.
While most low pressure centers are associated with fronts, others develop in response to a rising column of warm air. Such isolated disturbances usually precede the development of tropical storms and "cutoff lows" over the Southwestern deserts play a major role in the annual monsoons of that region.
