Why change the trend in predictions when the weather pattern is fairly stable? That’s likely one reason why forecasters in the National Oceanic and Atmospheric Administration Climate Prediction Center are holding with better-than-even odds for warmer-than-normal temperatures across Indiana in September, notes Ken Scheeringa, associate climatologist in the Indiana State Climate Office.

Forecasters place the odds at 30% to 40%. Think of it in terms of a daily forecast. Whenever a daily forecaster predicts rain, he or she always adds a percentage tag to it. That helps indicate how likely it is that the event will actually happen.

Truth is that according to forecast maps issued recently, all of the U.S. is likely to be above-normal for average temperature in September. Indiana is in a small band of states where the difference above normal may be slightly smaller than across the rest of the country. The deviation from normal could be strongest, if the forecast proves accurate, along the East Coast and in part of several states in the western Corn Belt and the Great Plains. 

Good news?
Warmer-than-normal temperatures could translate into average to slightly above-average growing degree day counts in September. In years when crops are on time or early, that’s hardly a factor. This year is different, Scheeringa notes.

With a reasonably high percentage of late-planted and replanted crops in Indiana and other parts of the eastern Corn Belt, a good dose of GDDs in September could be crucial. Late-planted crops will be packing in a final yield punch. And then some may race the calendar to reach maturity before frost.

Remember that even if the warm trend proves true, it doesn’t guarantee there won’t be cool days embedded within the month, Scheeringa points out. Forecasters are looking at deviations from normal, and can’t see individual cool days or even a cool week that far in advance.

There isn’t much to say about precipitation forecasts at this point, Scheeringa notes. For precipitation, there is an equal chance that Indiana will be above normal, at normal or below normal for September, he says. Long-term forecasters couldn’t find solid reasons to predict either higher or lower precipitation trends for the month.