There is an old wives tale that cows lying in a field is a sign of coming rain.
There are a lot of theories as to why cows might lie down before the rain hits:
Perhaps cows can sense increasing air moisture, realizing it’s about to rain and get everything wet. This theory states that cows plop down to preserve a dry patch of grass, though it’s unclear why a now wet cow would care about dry grass to munch on.
No, no, they’re hunkering down to stay warm, not to protect the grass, others interject. Yet cows enjoy cooler weather, sticking close to misters in barns or a shady patch in a field when the weather is warm.
Another theory states that cows lie down to help ease their stomachs. Some believe their four-chambered stomachs are sensitive to changes in atmospheric pressure, such as changes brought on by rainfall. This theory is similar to the belief that people can predict the weather because they “feel it in their bones.”

However, it may be as simple as the fact that cows lie down a lot. Cows lying down in a field may just be chewing their cud, settling in for the day, not preparing for rain. It just so happens to rain while the cows are relaxing.
It’s not that strange. Cows sleep on the ground, not standing—at least, not normally. Cows spend up to 12 hours a day lying on the ground, relaxing and napping. That’s why farms provide comfortable bedding in barns for when cows are not out in the field. Those beds will be happily used.
Yes, cows lie down when it’s going to rain. They also lie down when it’s going to be sunny, partly cloudy, and every other forecast you can think of. So when passing by a field of cows on a sunny day, don’t worry about your outdoor plans being rained out at the sight of a lounging cow. She’s enjoying her day, as you should, too.