Fall’s chill elusive with high pressure in place
It’s finally fall, but Mother Nature hasn’t gotten the memo yet.
Normally, morning low temperatures start to come down significantly by the end of September.
In fact, the average low temperature for Sept. 27 is 67 degrees, and the average will fall to 65 degrees by Sept. 30.
But as we all know, this year has not been “average” in San Antonio. Instead of being in the 60s, low temperatures have been in the middle to upper 70s for the past week, nearly 10 degrees above where they should be in late September.
Even in the past few years, San Antonio has been treated to cooler fall air by this time of the year.
A year ago, temperatures fell to 61 degrees on Sept. 27. In 2021, temps fell all the way to 56 degrees on Sept. 23. And the year before that, temps fell to a chilly 51 degrees on Sept. 30, 2020. This year, no such luck.
This is happening for a few reasons.
First of all, high atmospheric pressure redeveloped over Texas just as we were breaking into fall.
This is more of a summertime weather pattern: The high pressure keeps sinking air in the atmosphere over San Antonio. As the air sinks, it compresses and warms up, which then pushes temperatures well above average.
Secondly, while a couple of cold fronts have made their way toward San Antonio, nearly all of them have stalled out a bit north of the Alamo City. This has allowed our predominant winds to keep coming in from the south, where warm Gulf of Mexico air is very humid, and that’s kept low temperatures quite warm.
What we haven’t seen yet is a cold front strong enough to bring northerly winds and much drier air into South Texas.
The drier air is able to cool down much quicker than humid air, leading to chillier mornings.
Unfortunately, winds generally continue to come from the south, which has kept the air warm and humid.
Not many changes are expected as we finish out the last week of September.
With high pressure in the middle of the country, high temperatures in San Antonio will stay well above average, coming in between 92 and 96 degrees each day through the end of the week and pushing into the weekend. Rain chances will stay low, but a few isolated showers and storms cannot be completely ruled out.