According to the NOAA Climate Prediction Center press release, La Niña conditions returned in August and are expected to gradually strengthen and continue into this winter. This La Niña event first appeared last summer and continued in fall, winter, and early spring. By May, it had faded away. In fact, from May to July La Niña was not present in the Pacific according to the Climate Prediction Center. Only in August did it seem to return.
While La Niña events can continue for more than one year, it is very rare for one to disappear in spring and then reappeared in late summer. In fact, there are no other case like this in the historical records that go back to 1950, according to one of the primary indices used to measure La Niña and El Niño.
If La Niña continues to redevelop, the impacts on Illinois could include a fall that is warmer and drier than average and a wet winter all along the Ohio River Valley. The next set of seasonal outlooks from the Climate Prediction Center will consider the redeveloped La Niña. The new outlooks will be released on Thursday of this week.
La Niña is the name given to abnormally cold waters along the equator in the eastern Pacific Ocean. The changing weather patterns associated with La Niña effect not only the Pacific Basin but the U.S. as well. See the Climate Prediction Center link for more information current conditions and possible impacts.