They say, "The day you go out is the day of the market," and this weekend's weather during San Antonio Fiesta is just that.

On Friday, it was warm enough to wear short sleeves, with temperatures over 80 degrees, but the atmosphere completely flipped in just one day.

Starting Saturday afternoon, the temperature suddenly dropped, and by night, thunderstorms and lightning brought the perceived temperature down to the 40s.

This isn't just simple "unpredictable weather"; it's a common climatic phenomenon in this area.

The characteristic Texas weather is fundamentally a clash between cold, dry air coming down from the north and warm, humid air rising from the Gulf of Mexico to the south.

When these two air masses meet, they don't just pass by. Rain, thunder, wind, and rapid temperature changes occur.

This situation follows that exact pattern.

The reason it was warm until Friday is that the warm air from the south was dominant.

The humid, warm air envelops the area, causing temperatures to rise naturally.

However, a "cold front" from the north comes down.

As this front passes over San Antonio, cold air pushes in over the warm air, creating strong updrafts.

This is the structure that produces thunderstorms and rain. It's not just rain; it's a process of air flipping.

So, as it rains, the wind picks up, lightning strikes, and temperatures drop rapidly.

"It's not the rain that makes it cold; it's the change in the front that makes it cold."

There's also a reason it feels colder at night. During the day, there's still some residual heat, but at night, as the sunlight disappears, the cold air settles in. Plus, with the rain, it takes away body heat more quickly. So it feels much colder than the actual temperature.

One more thing to note: in Texas, wind is a variable. It's not just the temperature that drops; the wind also picks up. This further lowers the perceived temperature. The feeling of 45 degrees is completely different with or without wind. This situation is a case where wind, rain, and temperature drops coincide.

When such weather hits a weekend filled with outdoor events like Fiesta, the perception is even more extreme.

What felt like "a bit chilly" during the day turns into "isn't this winter?" at night.

There are always people who struggle because they went out unprepared. Such occurrences happen more frequently in the spring season. This is because the transition between seasons makes air flow more unstable.

So, people living in this area should remember one thing: "Don't just check the weather today; look at the air flow."