Stanford University PhD candidate Daniel Swain and his colleagues looked at patterns of high and low pressure over the Northeast Pacific and western U.S. during the October to May wet season from 1949 to 2015. They compared the patterns from the top five driest, wettest, warmest, and coldest years to those from all the other years in the record to see if they have tended to pop up more or less frequently over time. While the patterns of high and low pressure from the wettest years didn’t show a significant change, the pattern of persistent high pressure ridges associated with the driest years happened more frequently in recent decades than in earlier ones, the team found