SACRAMENTO, Calif. — September is a month that usually sees the changing of the seasons as hotter days slip away and milder temperatures become more common. The average high to start the month is 92°, but by the end of the month, our average high drops to 85°.
Average monthly rainfall is still a paltry 0.15", but even that is more than August's 0.02".
The stats back up September as a turning point from summer to autumn, with temperatures coming down but rainfall is still usually pretty hard to come by.
But specifically about the 100-degree heat, we must be almost done with this, right? Well... maybe.
Climatologically speaking, we should be about done with our triple-digit days.
Since 1990, Sacramento's average last 100°+ day is September 15. However, we've seen 100° as late as early October. The latest last 100°+ day in Sacramento since 1990 was October 10, 1991.
And we've seen some truly historic heat in September. It was in September 2022 that we set the all-time hottest temperature in Sacramento at 116°!
However, there's one thing we've got that plays into our favor: the sun. Or perhaps more accurately, the Earth's tilt.
A big difference between triple-digit days in September vs. triple-digit days in July and August is that the days are now getting shorter.
Between the summer solstice on June 20 and the upcoming fall equinox on September 22, Sacramento has 2 hours, 46 minutes, and 47 seconds less daylight. That's almost 3 hours less of heating, so even when we get to 100°, it's typically only for a couple of hours or so in the afternoon.
Compare that to the peak of summer when we have almost 15 hours of daylight, allowing us to stay in the triple digits for several hours in the afternoon and early evening.
But we also know that climate change is prolonging the September heat.
The average max temperature in Sacramento for September before 1970 was 85.2°. Since 1970, the average max temperature is 89.0°, a change of almost 4 degrees. You can think of this as meaning each day in September is now 4 degrees warmer in Sacramento than 50 years ago. This shifting baseline makes it easier for us to see some extreme heat in September.
So it's no guarantee — and with climate change, we're more prone to warmer temps — but generally, September sees the end of the triple-digit heat and a transition to cooler weather. Here's to hoping!
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