"Atmospheric rivers are long streams of water vapor that form at about one mile up in the atmosphere. They are only 250 miles across but extend for thousands of miles—sometimes across an entire ocean basin such as the Pacific. These conveyor belts of vapor carry as much water as 10 to 15 Mississippi Rivers from the tropics and across the middle latitudes. When one reaches the U.S. West Coast and hits inland mountain ranges, such as the Sierra Nevada, it is forced up, cools off and condenses into vast quantities of precipitation."
I don't think Pineapple Express is really deprecated in meteorology for PC reasons, just informal. Weather reporters in Northern California still use it on air from time to time. Also atmospheric river is hypernymous to Pineapple express, the latter being a particular example of the former