If you hate summer — and if you’re one of those ladies who is already looking forward to pumpkin spice season — you have plenty of reasons for optimism. With no reason to think that extreme heat will linger into the fall season this year, summer truly appears to be on borrowed time.
The remnants of Hurricane Ida have given us a nice taste of fall the past couple of days, with temperatures hovering just above 70°. We’ll gradually warm up over the next couple of days, but the benefit of the exiting tropical system will be lowering humidity values. That’s going to usher in some cooler nights, which is going to be yet another taste of early fall.
Beyond that, there are two reasons why we can say, with reasonable assurance, that summer is on borrowed time.
One is climatological. Today is the first day of fall on the meteorological calendar. We’re in that time of year where the days are growing shorter and the sun is sinking lower in the sky. One month ago today, the sun set at 8:45 p.m. Today, the sun will set at 8:07 p.m. In just one more month, the sun will set at 7:24 p.m.
Photoperiodism is the scientific term for it. As the earth tilts on its axis and the sun moves further south in the sky even during the middle of the afternoon, it becomes harder for extreme heat to build in … and easier for refreshing waves of cooler air to penetrate from the north. Photoperiodism, of course, doesn’t have anything to do with temperatures; it’s a reference to lengthening nights, and it triggers the autumn season. But cooling temperatures are a byproduct of photoperiodism.
Climatology isn’t a guarantee of cooler temperatures, of course. Two years ago we experienced a ridiculously hot start to fall. Temperatures were almost 10° above normal for the entire month of September, and we experienced temps in the 90s for the first four days of September (and in the upper 80s for three more days after that) before the heat wave finally broke for good. Five years ago (2016), the year of the wildfires, was another ridiculously hot — and dry — fall.
But, in an average year, the heat peaks in August, and begins to wane after that. Our average temperature for Sept. 1 is 83° in Oneida, already down three degrees from the peak seen a few weeks ago. By the middle of this month, the average temp has dropped below 80°. Then the cool-down accelerates. By the end of the month, we’re in the mid 70s on an average day. And by the middle of the next month, we’ve dropped into the 60s. That’s an average temperature drop of about five degrees every two weeks, beginning Sept. 1.
And that brings us to our second reason: seasonal outlooks. We know we’re moving into the time of year where we typically see summer patterns start to break down. Yet at this same time in 2019 (and in 2016) we could look ahead and anticipate that we were in for a hot autumn.
How about this year? Well, consider the current outlook from the National Weather Service’s Climate Prediction Center:
That’s the temperature outlook for the Day 8-14 period, which takes us through Sept. 14. The Day 6-10 temperature outlook is much the same. Keep in mind that the blue represents the probability of below-average temperatures, not the actual degree of below-average temperatures. So just because we’re swathed in blue doesn’t mean we’re going to be cold during the first part of September. But what that forecast does tell us is that there’s a fairly likely chance of below-average temperatures overall for the first half of the month. That may mean temperatures around 80° to 82° or so, but it also means that a major heat wave is unlikely. In fact, the heat is likely to be centered over the western U.S. for at least the first half of the month. That’s not necessarily good news for the ongoing wildfire suppression efforts out west, but the good news is that the CPC is forecasting above-average rainfall chances for the Sierra Nevada region for the next couple of weeks.
As we move deeper into the month, the CPC’s outlook for September as a whole is more of the same: the heat will be relegated to the west, with a chance for below-average temperatures over much of the Southeast.
I look at the end of summer weather pattern the same way as I look at the end of winter weather pattern: in degrees of probability based on climatology. With regard to summer, the deeper we get into fall, the lesser the chances of extreme heat. So if we make it through the month of September without massive heat waves building over the South, as the CPC thinks we will, summer is just about going to be completely out of time.
Oh, we’ll undoubtedly experience “Indian Summer” just as we always do. It’s amazing what an 80° day feels like in October as compared to August. It’s all about how our bodies quickly become acclimated to the weather.
Still, if I were a gambling man and someone asked me to wager on whether we’d see anymore 90° days this year, I’d take that bet. It could happen, but the chances are low. I’d feel comfortable betting that we’re going to end 2021 with just five days of temperatures in the 90s. That’s pretty incredible, especially when you consider that August was actually a hot month overall.
The bottom line: We’re on the downhill slide towards winter. The dog days of late July and August are behind us. September always has a few hot days in store, as anyone who spends much time outside during the early part of the month can attest. But, for the most part, September is a transitional month that leads us further away from summer’s heat and closer to the autumn foliage season of October. And, unlike 2016 and 2019, there’s no reason to think this year is going to be an exception to the norm.