La Nina weather patterns tend to bring wetter than normal conditions for the northern half of the U.S. and drier than normal conditions for the southern half, with the dividing line falling on Colorado’s equator, Summit Daily’s Luke Vidic reports. The National Ocean Service explains that “During La Nina events, trade winds are even stronger than usual, pushing more warm water toward Asia. Off the west coast of the Americas, upwelling increases, bringing cold, nutrient-rich water to the surface. These cold waters in the Pacific push the jet stream northward. This tends to lead to drought in the southern U.S. and heavy rains and flooding in the Pacific Northwest and Canada. During a La Nina year, winter temperatures are warmer than normal in the South and cooler than normal in the North.”
La Nina is not good news for the Western states that rely on Colorado River water who have already been hit with drastic reductions of their water entitlements. If La Nina happens again this winter, it will be the third year in a row — a rare event and one that will decrease snowmelt essential for the system’s water supply. While forecasters are not 100% certain that La Nina will occur for the third straight year, water planners in states such as Arizona have concluded that it is likely to happen and will cause the state to continue to experience chronic drought.
The National Weather Service‘s latest outlook reports that La Nina conditions are expected to persist throughout the remainder of 2022. As a result, “the outlook for the fall rainy season favors below normal precipitation,” the agency predicts. (Map at top of this article from the National Weather Service’s La Nina advisory page).