Forecasters from the National Oceanic and Atmospheric Administration indicate there is a 55% to 65% chance that weak La Niña conditions will develop during the fall/winter of 2017-2018, according to the agency's latest monthly update and diagnostic discussion released Oct. 12. This compares to a 55% to 60% likelihood of development from the agency's prior monthly discussion.
NOAA said that while the ocean and atmosphere system remains consistent with El Niño-neutral conditions, La Niña conditions are beginning to emerge.
"These forecasts are supported by the ongoing easterly wind anomalies across portions of the Pacific Ocean and the reservoir of below-average subsurface temperatures. In summary, La Niña conditions are favored (55-65%) during the Northern Hemisphere fall and winter 2017-18," the diagnostic discussion said.
Defined by cooler sea-surface temperatures in the equatorial Pacific Ocean, a La Niña event often brings more supportive fundamentals for U.S. natural gas and electricity markets, including a higher probability of colder winters, hotter summers and increased tropical activity in the Atlantic basin.
"The dynamical computer models are not very clear on which way sea surface temperatures will go for the next month or so … However, the models are more consistent after October, predicting that the most likely outcome for the late fall and early winter is sea surface temperatures below the threshold for La Niña," according to an Oct. 12 blog post from NOAA.
Meanwhile, although warmer-than-normal weather is eyed across much of the United States through the end of October, below-average temperatures are anticipated for a majority of the country by December, according to recent forecasts from The Weather Company.
"As is typical in emerging La Niña events, we expect a warm October across most of the eastern U.S., resulting in a slow start to the heating demand season. By later in the fall, we expect the pattern to drive cooler-than-normal temperatures in the eastern U.S., with these below-normal temperatures becoming more widespread in December," Todd Crawford, chief meteorologist at The Weather Company, said in the Sept. 26 outlook.