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We've made it through several days of our Weather Folklore series, and today's saying is a perfect example of how a little bit of real meteorology can turn into a much bigger prediction once it's been passed down through generations. You've probably experienced this before: It's a hot summer afternoon, the sun is shining brightly, and suddenly... it's raining. Then somebody says: "If it rains while the sun is shining, it'll rain at the same time tomorrow."

I've heard several variations of this one over the years, but they all make essentially the same prediction. A sunshower today means you can expect another shower at about the same time the following day. But can one sunshower really predict tomorrow's weather down to the hour?

First... Why Does It Rain While the Sun Is Shining?

There's actually nothing unusual about the meteorology behind a sunshower. Rain doesn't necessarily have to be falling from a cloud directly over your head. Sometimes wind can carry raindrops away from a nearby shower into an area where the sky is clearer. Other times, a small shower may be overhead while enough of the surrounding sky remains clear for sunlight to reach you.

That's especially easy to accomplish during summertime when we're dealing with scattered, relatively small showers and thunderstorms. You can be standing in the rain while someone a couple of miles down the road is sitting underneath blue skies. And if the sun is positioned correctly behind you, all of those raindrops can also give you one of the best parts of a sunshower: a rainbow. 🌈

Where Did This Saying Come From?

Pinning down the exact origin of the "same time tomorrow" portion of this folklore is difficult. Unlike some of the sayings we've covered (such as "Red sky at night, sailor's delight") there isn't one well-documented historical source. Sunshowers themselves, however, have inspired folklore across cultures for generations. The unusual combination of bright sunshine and falling rain has accumulated dozens of regional sayings and explanations around the world.

The idea of rain returning around the same time the following day probably grew from something people really did observe, especially during summer. And this is where today's folklore gets a little more interesting.

Could It Rain Around the Same Time Tomorrow?

Absolutely. But not because it rained while the sun was shining today. During the summer, showers and thunderstorms across Southern Middle Tennessee are often diurnally driven. That's meteorologist-speak for storms that are heavily influenced by the daily heating cycle. The sun comes up. The ground heats up. Temperatures climb. Instability builds.

Eventually, the atmosphere becomes unstable enough for scattered showers and thunderstorms to begin bubbling up—usually during the afternoon and early evening. Then the sun goes down, the atmosphere begins cooling, and most of those storms disappear.

The next day? We heat everything up and potentially do it all over again. That's why we can sometimes have thunderstorms develop at 2 or 3 PM several days in a row.

But Here's the Problem...

Seeing a sunshower at 3:17 PM Monday doesn't mean Mother Nature has scheduled another one for 3:17 PM Tuesday. Where individual summertime storms develop depends on countless small-scale factors: moisture, instability, leftover outflow boundaries from previous storms, terrain, cloud cover, subtle disturbances in the atmosphere, and even where earlier storms happened to develop. Those ingredients can change dramatically in 24 hours.

That's why a forecast calling for a 30% chance of thunderstorms Tuesday afternoon doesn't mean the same neighborhoods that got wet Monday will get wet again. In fact, summertime rainfall is notorious for enormous differences over very short distances.

What Does the Climate Data Tell Us?

Here's where this folklore probably earned its reputation. August is still a relatively wet month in our part of the country. Just south of Southern Middle Tennessee, Huntsville's official 1991–2020 climate normals show an average of about 3.55 inches of precipitation during August. That means there are plenty of opportunities for scattered summertime rainfall. Combine that with storms frequently favoring the afternoon heating cycle, and it's easy to understand how someone could see a sunshower one afternoon and another shower around roughly the same time the following day.

Do that a few times, and you've got yourself a weather saying. But there's no established relationship in climate data showing that a sunshower on one day specifically predicts rainfall at the same time the next day. The repeated weather pattern can predict another opportunity for rain. The individual sunshower cannot.

The STN Weather Verdict

Scientific Rating: ⚠️ Mostly False — With a Tiny Grain of Truth. A sunshower today does not mean it'll rain at the same time tomorrow. There's simply no physical mechanism connecting the two events that way. However, I can see how this folklore developed. During summertime, the same hot and humid air mass can remain overhead for several days. Since daytime heating frequently triggers storms during roughly the same afternoon window, rain can occur around the same time on consecutive days.

So if Grandma swore this one worked, she wasn't necessarily imagining things. She was probably noticing the daily heating cycle without knowing there was a meteorological term for it.

A Quick Look at the Forecast

Ironically, our current forecast is a pretty good example of the science behind today's folklore. Scattered showers and thunderstorms will remain possible during the afternoon and early evening over the next couple of days, with the highest chances generally along and east of Interstate 65. Coverage will remain fairly limited, though, meaning plenty of communities will stay completely dry. The bigger weather story this week is quickly becoming the HEAT. 🥵

A strengthening ridge of high pressure will gradually suppress rain chances later this week while temperatures climb into the middle and potentially upper 90s. Combine that with dew points well into the 70s, and heat index values will routinely climb above 100 degrees. A Heat Advisory begins Tuesday for much of Middle Tennessee west of the Cumberland Plateau, where heat index values could reach 105–109 degrees in some locations.

The ridge looks to strengthen even more later this week and into the weekend. Rain chances should fall into the 10–30% range while the heat becomes increasingly oppressive. Some guidance even suggests actual temperatures could make a run toward the upper 90s (and perhaps flirt with 100 degrees in the hottest locations) by the weekend.

The Bottom Line 🧾

🌦️ Folklore: If it rains while the sun is shining, it'll rain at the same time tomorrow.
🌈 What's happening: It's called a sunshower, and there's a perfectly normal meteorological explanation.
⏰ The grain of truth: Summertime storms often develop during roughly the same afternoon hours on consecutive days because of daytime heating.
❌ The problem: Today's individual sunshower cannot predict where—or exactly when—tomorrow's storms will develop.
⚠️ STN Weather Rating:Mostly False, with a tiny grain of truth.
🥵 Forecast: Scattered afternoon storms remain possible early this week before rain chances trend downward and dangerous heat becomes the main weather story later this week.
📰 Reminder: The Southern Tennessee Weather Blog, presented by Heritage South Community Credit Union, is updated Monday through Friday with fresh, locally tailored forecasts you can trust.

Weather Folklore: Sunshower Today, Rain Again Tomorrow?