Goodbye meteorological summer, hello hints of fall
Labor Day weekend is upon us, an American holiday of leisure that often feels like the last push of summer and unofficial start of fall.
In a way, it is, especially this year, as meteorological fall begins on Labor Day, Sept. 1, and runs through November 30.
Meteorological seasons are based on annual temperature cycles and are useful for keeping consistent weather and climate records. By contrast, astronomical or ‘traditional’ seasons are based on Earth’s position relative to the sun.
This year, the autumn equinox falls on Sept. 22, a day when darkness and daylight hours are nearly equal for much of the globe. Around 30 degrees latitude, daylight will last 12 hours and eight minutes, while nighttime will last 12 hours and six minutes. For Northwest Missouri and Northeast Kansas, which are located around 40 degrees latitude, these times are adjusted slightly.
The fall equinox is still over three weeks away, but as we get closer, daylight hours will continue to get shorter, quickly. In the next month, we’ll lose about an hour and 15 minutes of daylight.
On Sept. 1, the sun will rise at 6:47 a.m. and set at 7:50 p.m. in St. Joseph. By the end of the month, sunrise isn't until 7:15 a.m., with sunset at 7:02 p.m.
As days grow shorter and nights longer, a few subtle changes start to take place, signaling the slow death of summer and the onset of fall. With longer nights, temperatures are able to cool by several more degrees, creating a large range between early morning lows and afternoon highs that often starts to manifest in late August.
Clear skies and relatively dry air can enhance this effect, as it did locally this past week with several early mornings in the 40s and 50s followed up by afternoon highs in the upper 70s to low 80s. Longer, cooler nights also increase the frequency of patchy fog development in the hours leading up to sunrise when the air is still and skies are free of cloud coverage.
