Fall is the one season of the year when the change in weather usually coincides with the change in the calendar. This year may be a little different, because summer is hanging tough amidst a very odd-looking weather pattern shaping up for the next week or two.
The autumnal equinox arrives Monday (you'll hear some say it's Tuesday, but that is wrong as it applies to us) September 22 at 10:29 PM. Click on the link for a good explanation of what that means in an astronomical sense. (Climatologically, all of September is considered an autumn month.)
From a weather perspective, the transition to fall in the Deep South almost always happens in the last 10 days of September. Most years it's a pretty abrupt change, but this year it's shaping up to be more gradual and possibly a bit indecisive.
Lucky for us, we will feel fall in the air much of this week. A cold front will sweep through here early Monday morning, bringing a reinforecement of the cool, dry air mass that was around for the first half of the weekend. (Sunday got a bit hot after our cool 62º morning low, Columbus's coolest temperature since May.)
Cool northeasterly winds will blow behind the front, keeping our highs barely above 80 all week as the air mass parks itself over the eastern half of the country and then hardly moves. Lows will initially make the 50s both Tuesday and Wednesday before persistent east winds bring back Atlantic moisture, thus sending lows back into the 60s the rest of the week. So this front on Monday does look like the first real fall cold front.
The reason that air mass becomes lodged in place is related to the upper air pattern. There will essentially be no jet stream available to facilitate the movement of surface features; the upper jet will be way up over Canada by late in the week. Below that here in the lower 48 we'll only have weak, smaller-scale disturbances driving our weather - a very stagnant type of pattern where much of the significant weather will take place over the West.
One thing that may change for us is an influx of Atlantic and tropical moisture by late in the week, related to the surface high. This could bring our next rain chances just in time for next weekend, and could also put a crimp in our fall like temperatures and lower humidity. Check out the long-range outlook for 8 to 14 days ahead, which basically predicts an early October heat wave for almost the entire eastern two-thirds of the country. If that does materialize, we may find ourselves wondering if summer is never going to go away.
This type of pattern can also be very favorable for tropical development, and I would not be surprised if there is a rash of late-season hurricane activity in October on the Atlantic side. Exactly where, nobody knows.
There's also the possibility the models could be wrong in the details, though they are probably right in the overall scheme. So enjoy the week we have coming, which will bring a bit of fall our way, though a round of any really chilly weather would still seem to be far in the future.