As it turned out, though, neither the cooler nor the warmer SSTs appear to be to blame for the 2020 “non-soon,” which has contributed to record July heat. Rather, this year’s moisture-thief is a high-pressure dome that settled remorselessly atop the Southwest throughout the summer months so far.
“Typically, high pressure will oscillate from northern Mexico into the Four Corners and even northern (Utah and Colorado) through the summer,” said O’Malley. That northward expansion of high pressure allows the thicker moisture to surge north periodically into Arizona.
But this year? “Persistent low pressure along the West Coast has kept the high situated more often in southern Arizona and New Mexico,” said the NWS forecaster. As a result, “the best moisture has been trapped in northern Mexico.”