Giant blob of cold water rises from the depths of the Pacific, possibly heralding the arrival of La Niña this fall

This animation shows how temperatures at the surface and subsurface of the tropical Pacific ocean departed from average over five-day periods starting in early August 2017. The vertical axis shows the depth below the surface in meters. The cross-section is right along the equator. Note the blue blob indicative of relatively cool water rising from the depths and spreading eastward. (Source: NOAA ENSO Blog) Here we go again? Following a mild and short-lived La Niña episode in 2016/2017, the climatic phenomenon stands a 55 to 60 percent chance of developing once again this fall and winter. That's the most recent forecast from the National Oceanic and Atmospheric Administration. Based on observations of what's happening in the Pacific Ocean, and modeling to predict what may be coming, NOAA's Climate Prediction Center has issued a La Niña watch, indicating that conditions are favorable for its development. La Niña can strongly shift weather patterns, bringing anomalously cool or warm, and wet or dry, conditions to large parts of the world. In the United States, La Niña tends to bring wetter than normal conditions to the Pacific Northwest and parts of the Midwest. Unfortunately for southern and central California, things tend to dry out.