When Ken Scheeringa looks at the long-term prediction maps from the National Oceanic and Atmospheric Administration’s Climate Prediction Center for December, he sees much of what he has seen during most of 2017. All of Indiana could be warmer than normal, and there is no indication as to which way precipitation might fall — above normal, below normal or just normal.
Scheeringa, Indiana’s associate state climatologist, says the only difference this time is that the odds of it being warmer than normal are slightly less than during November. There’s a 33% chance.
That may not make sense until you put it in the context of a daily weather forecast. Some weather forecasters on TV get excited if there is a 30% or 40% chance of rain. Often it doesn’t rain, at least not at your place. Looking back, it’s hard to say the forecaster was wrong because he or she predicted at less than 50% odds that it would happen in the first place.
What this long-term forecast says is that there is a better chance Indiana as a whole will average warmer-than-normal temperatures when the entire month of December is averaged together than anything else. But there is certainly no guarantee.
Variable weather patterns
Scheeringa notes that even if the daily temperature averages only 1 degree higher for the month, the forecast would be right. Among those 31 days that are averaged together, there may be a warm spell or two, but there may also be cold days.
Unseasonably cool weather followed by unseasonably warm weather has been the trend all year long. It helped make for an unpredictable and somewhat topsy-turvy growing season. Some areas also ended up on the dry side, even though that wasn’t predicted. On the other hand, some areas were wet if you compare to averages.
Scheeringa says predictions are usually more accurate when certain factors that affect Midwest weather are more pronounced, such as the El Niño-La Niña cycle. Right now it remains in a neutral phase, making it harder to hang a hat on a trend going one way or the other.