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One of the things I've enjoyed most about this new Weather Folklore series is discovering that not every old weather saying is completely made up. Some have surprising scientific explanations, while others simply don't hold up when you compare them against decades of weather records. Today's saying is one I've heard countless times across Tennessee: "If it rains on the first day of the month, it'll rain 15 days out of that month."

It's an oddly specific prediction. Fifteen days? Why not ten... or twenty? So let's take a look at where this saying came from and whether the atmosphere actually keeps track of what happens on the first day of the month.

Where Did This Saying Come From?

Unlike some folklore we've covered earlier this week, this one doesn't have a clearly documented origin. Most historians believe it developed from generations of farmers carefully observing weather patterns before modern forecasting existed. If the month began wet, many assumed the atmosphere had settled into a wetter weather pattern that would continue for weeks.

In many parts of the eastern United States, weather patterns often do persist for several days or even a couple of weeks. That probably helped reinforce the belief over time. Eventually, the idea became simplified into a memorable rule: Rain on the first day... rain on half the days of the month.

STNWX WEATHER FOLKLORE - IF IT RAINS ON THE 1ST DAY OF THE MONTH IT’LL RAIN 15 DAYS OUT OF THE MONTH

Is There Any Science Behind It?

Not really. While weather patterns certainly can persist for several days, there's nothing special about the first calendar day of a month. The atmosphere doesn't know when one month ends and another begins.

Storm systems, jet streams, high pressure, low pressure, and climate patterns all evolve continuously. They don't reset when the calendar flips from July 31st to August 1st. Sometimes a rainy first day simply happens because you're already in a wet weather pattern. Other times it's just one isolated thunderstorm before two weeks of sunshine.

What Does the Climate Data Say?

Looking at long-term climate records, there's no statistical relationship showing that rain on the first day of a month means you'll receive rain on exactly 15 days during the rest of that month. In fact, many locations across Tennessee average fewer than 10 measurable rainfall days during August despite frequently beginning the month with scattered thunderstorms. Other months (particularly during the winter and spring) may naturally have 12 to 15 rainy days regardless of whether the first day was wet or dry.

The number simply doesn't hold up consistently when compared against decades of observations. Meteorologists have studied rainfall frequency extensively, and no known climate research supports this particular rule.

Why Do People Think It Works?

This is actually a great example of something called confirmation bias. If it rains on August 1st and the month turns out fairly wet, people remember it. If it rains on the first and the next three weeks are sunny and dry... most people quickly forget.

Our brains are naturally wired to remember the "hits" much more than the "misses." Over time, those memorable successes make the folklore feel much more reliable than it actually is.

The STN Weather Verdict

Scientific Rating: ❌ False! There's no meteorological reason that rainfall on the first day of the month should determine how many rainy days occur during the rest of that month. Weather patterns can certainly remain active for several days, but the calendar itself has no influence on the atmosphere.

It's an interesting piece of folklore—but not one you should use to plan the rest of your month.

Forecast over the next 7 days

Speaking of rainy days, our forecast continues to look like a typical August pattern across Southern Middle Tennessee. This afternoon will feature another round of scattered showers and thunderstorms, although many communities west of Interstate 65 will stay dry while the better coverage develops farther east. Any storm that forms will be capable of producing heavy downpours, frequent lightning, gusty winds up to around 40 to 50 mph, and localized flash flooding.

Saturday brings a slight change to the pattern. A weak disturbance moving in from the west should help spark scattered showers and thunderstorms across the entire area, rather than focusing mainly on our eastern counties. It won't be a washout, and most outdoor events should be able to continue as planned, but keep an eye on the radar and have a place to shelter if storms move nearby. Looking ahead into early next week, isolated to scattered rain chances will continue while temperatures climb back into the lower to middle 90s. Heat index values will likely reach the 100 to 105 degree range Monday and Tuesday, making those our hottest days of the upcoming week.

The Bottom Line 🧾

🌧️ Folklore: "If it rains on the first day of the month, it'll rain 15 days that month."
🌾 Origin: Likely developed from farmers observing extended wet weather patterns.
📊 Science: The atmosphere doesn't follow the calendar, and long-term climate records show no consistent relationship.
❌ STN Weather Rating:False
🌦️ Forecast: Typical August weather continues with scattered afternoon storms each day, a slightly wetter Saturday, and hotter conditions returning early next 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: Does a Rainy First Day Predict the Month?