Like politics in the U.S., the ocean temperature off the equatorial Pacific is always changing. And, like the result of many elections, the impact of this sea shift is difficult to predict.

Related: Climate Center increases likelihood of La Nina to 75%

A very strong El Nino warming finally ended this year after a 19-month run. A La Nina cooling phase may already be underway. What if anything that means for grain prices is murky, at best.

Some of the most widely viewed La Nina maps look at weather impacts – where it’s warmer or cooler than normal, where it’s wetter or drier. Instead, we examined how crops actually fared when a La Nina occurred: Were yields better or worse than normal?

The results are shown on the map below. But don’t start betting on these yet. First, the statistical significance of these connections is fairly weak. That means the tie between La Nina and yields may be just the result of chance.

Perhaps even more important: Forecasts are changing just like presidential polls.

Related: As El Nino exits, La Nina looms

A cooling in September of sea surface temperatures in the equatorial Pacific Ocean now has weather forecasters raising the possibility of a La Nina event this fall at 70%, which is a change from a month ago when they said there was a 55% to 60% chance it would not happen this year.

La Nina is the abnormal cooling of the sea surface in the equatorial Pacific Ocean. La Ninas are often milder than El Ninos but have been associated with lower-than-normal winter temperatures in the northern United States and warmer-than-normal temperatures in the Southeast.

“Atmospheric anomalies across the equatorial Pacific edged toward La Niña during September, with a stronger tendency toward La Niña late in the month,” the National Oceanic and Atmospheric Administration’s Climate Prediction Center said its monthly report released on Thursday.

It went on to say the La Nina may be a weak one and there was a 55% chance that it would last through the 2016/2017 winter.

“The forecaster consensus now favors the formation of a weak La Niña in the near term, becoming less confident that La Niña will persist through the winter,” it said.

Related: Global Hot Spots: La Nina expected August-October