September has arrived in Perry County, and with it comes one of my favorite transitions of the year. We are moving from the heat and humidity of summer toward the cooler, drier weather of autumn, but Missouri rarely makes that transition all at once. September can bring summer-like heat one day and a refreshing taste of fall the next, which makes this one of the most interesting months of the year to watch the weather.
For Perry County, I expect September to be a changeable month with a warmer-than-normal, particularly early and through portions of the middle of the month. That does not mean every day will be hot. Normal temperatures decline significantly as we move through September, and each strong cold front will have a greater ability to bring cooler air into Southeast Missouri. The bigger story will be the back-and-forth between lingering summer warmth and increasingly frequent pushes of autumn air.
The heat is not finished with us yet. Temperatures in the upper 80s and 90s remain possible, especially during the first half of the month, and a warm spell later in September cannot be ruled out. At the same time, I will be watching for those first substantial cold fronts that bring lower humidity, cooler mornings and noticeably more comfortable afternoons. Eventually, those cool-downs will begin lasting longer, which is one of the best indications that autumn is gaining the upper hand.
Rainfall will be another important part of the September forecast. This is typically a transition toward a drier pattern, but September can still produce heavy rain from thunderstorms, slow-moving fronts or tropical moisture moving northward from the Gulf of Mexico. A tropical system does not have to come anywhere near Perry County to affect us. Its remnants can interact with a cold front and produce a period of heavy rain across Missouri. I will be watching both our regular frontal systems and the tropics throughout the month.
Severe thunderstorms also remain possible. While the frequency of severe weather generally decreases from the summer months, a strong September cold front moving into warm, humid air can produce an organized line of thunderstorms with damaging winds, lightning and heavy rainfall. The arrival of autumn does not mean the severe weather season is immediately over.
One of the biggest changes we will notice this month will come from the sky rather than the thermometer. Daylight continues to decrease throughout September as the Sun’s path across the sky becomes lower. The autumnal equinox arrives September 22, marking the astronomical beginning of fall, although meteorological autumn began September 1. Those shorter days will gradually reduce daytime heating and help set the stage for cooler temperatures later in the season.
September is also a wonderful month to look up after dark. The longer nights give us more opportunities to see the stars, and Perry County’s rural areas can provide some excellent viewing when skies are clear. Venus will be exceptionally bright in the evening sky this month, while Saturn will also be prominent. Jupiter and Mars are better positioned for early-morning viewing. The full Harvest Moon arrives September 26 and will appear near Saturn in the evening sky, providing a particularly nice opportunity to step outside and look up.
As the month progresses, keep an eye on the landscape as well. The first hints of fall color can begin appearing in September, although the peak of autumn color will come later. Cooler nights and decreasing daylight will gradually signal the trees begin preparing for winter. The change may start with only a few leaves here and there, but it is one of the first visible reminders that the season is turning.
And then there is the weather folklore that always seems to become more interesting as summer fades. September is when we hear about woolly bears supposedly predicting the coming winter, squirrels gathering large quantities of nuts before a harsh winter, birds changing their flight patterns and insects becoming more active before weather changes. These are traditions rather than reliable forecasting tools, although animals really do respond to changes in temperature, daylight, pressure and food availability. I enjoy the folklore because it reminds us how closely earlier generations watched nature before radar and satellites became part of everyday forecasting.
My September outlook for Perry County is therefore one of transition. I expect we will have more heat before summer finally gives way, but I also expect several increasingly noticeable cool-downs along the way. Rainfall may come in bursts rather than evenly throughout the month, and the threat for thunderstorms will remain, particularly when strong fronts encounter warm and humid air. By the end of September, however, I expect the signs of autumn to be much harder to ignore.
That is what makes September special in Missouri. The season does not simply change because the calendar tells it to. It happens gradually, through the cooler morning after a cold front, the earlier sunset, the first changing leaf, the clearer night sky and the first evening when you realize you need a light jacket.
So, as you go through September, watch more than the thermometer. Watch the sky, listen to the weather, notice the changing daylight and take a moment to look at the Moon and stars. Summer may still have a few surprises left for Perry County, but autumn is already making its presence known, and from my window, I will be watching that transition very closely.
