The autumnal equinox happens over the weekend, at 8:54pm CDT Saturday evening, putting us officially into the fall season (regardless of how it feels outside)! An equinox occurs when the Earth is neither tilted toward or away from the sun.
The Earth is tilted by 23.5 degrees on its axis, which why we have seasons in the first place. When the northern hemisphere is tilted toward the sun, we’re in summer; when the northern hemisphere is tilted away from the sun we get winter. The equinox is the moment between, when both hemispheres receive the same amount of sunlight. During the equinox, the sunrise and sunset also appear at due east and due west respectively.
Although equinox does translate out to “equal night” the equinox is not actually a day of equal day and night for all us of. That day also depends on your latitude. For Huntsville, our day of equal daylight and night will come 4 days after the equinox on September 26th. After this day we’ll experience more night hours than daylight hours until the winter solstice.
Between now and the winter solstice Huntsville’s average temperature will drop by about 30 degrees, from 83°F to 52°F. We’ve been well above average through most of September though; as of now, September’s high temperatures come in about 5°F above the 30-year average. Is this an indication of a warm fall season ahead? Not necessarily.
The climate prediction center gives us a 33-40% chance of seeing a warmer than average fall season, but there are still a number of uncertainties that could impact our weather in the coming months.
One of these is the often talked about El Nino Southern Oscillation (ENSO) pattern. Right now we’re under neutral conditions, but there’s a chance that an El Nino could develop. A neutral pattern can translate to a slightly warmer and wetter fall season around here, while an El Nino can translate into a slightly warmer and drier fall season. There’s not a high level of certainty regarding the ENSO forecast for the coming months though.
More local influences could impact the fall season too. For example, moderate drought conditions have developed over North Alabama. Drier conditions often lead to cooler nights, but warmer afternoons, since drier air tends to heat up and cool off more easily than moist air.
A shift in any one factor can change the seasonal outlook, so it’s really better to check your local forecast regularly. If we see a reliable indication of cooler weather on the horizon we’ll be sure to give you a heads up! For now, you’ll likely have to at least wait until early October to get a hit of crisp, cool fall air.