The National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Center recently issued a La Niña watch, stating the odds are favorable for the event forming in late fall and continuing through the winter.
According to NOAA forecasting models from the North American Multi-Model Ensemble and some models from international partners, there is a 51 percent chance of the onset of La Niña during the fall and a 66 percent chance of it continuing into winter 2021-22.
El Niño Southern Oscillation (ENSO) neutral conditions—when seawater temperatures are average and sometimes called La Nada—are forecast to persist through the summer until La Niña takes over later this year, forecasters said. Sub-surface waters are currently warmer than average, except for the eastern Pacific, where cooler-than-average waters have started developing.
Although it is several months away yet, a typical La Niña winter in the U.S. brings cold and snow to the Northwest and unusually dry conditions to most of the Southwest, which is already feeling the effects of last year’s event. Last year’s La Niña was a “moderate to strong event” through March and resulted in an above-average snowpack for the Pacific Northwest and parts of the Rockies.
Thus far, winds in the upper atmosphere and across the ocean are about average temperature, so it is difficult to predict how the jet stream will affect the weather pattern in fall and winter. Meteorologists will have to wait until fall when NOAA expects La Niña to set up before they can have a better picture of the jet stream.
Back-to-back, La Niña events are not unusual, according to Tom Di Liberto of NOAA’s Climate Program Office.
“In fact, of the twelve first-year La Niña events, eight were followed by La Niña the next winter, two by neutral, and two by El Niño,” wrote Di Liberto. “Honestly, with those numbers, it would have been more surprising if we thought neutral conditions would continue all year.” — Charles Wallace, WLJ editor