Predict Weather Just by Drinking Coffee?! It's Actually True!

It's late March again, and the Qingming Festival is just around the corner. The saying "Qingming season brings continuous rain" is not merely poetic. Many people in Guangdong Province have likely just sat through several days of downpours. Open the weather forecast and you see a whole week of rain — enough to try anyone's patience.

Yet forecasts are often unreliable. Just as you decide to head out, the sun comes out. That plants a tempting thought: "Skip the umbrella, you'll be back soon, it won't rain." Shortly after you leave, the sky turns on you and a downpour begins.

When you face that uncertainty — a forecast calling for rain, but no way to know whether it will actually fall during your outing — you can simply make a cup of coffee. With one cup of coffee and a sugar cube, you can predict the short-term weather.

The Science Behind the Trick

This life hack comes from the book "A Cup of Coffee Knows the Weather" by the British author Matthew Cole. In it, Cole writes: order a cup of coffee, drop in a sugar cube, and watch the bubbles released as the sugar dissolves — without stirring. If the bubbles gather in the center, it signals high atmospheric pressure and the weather will soon clear. If they collect around the rim of the cup, it signals low atmospheric pressure and heavy rain or snow is on the way.

Some might think this sounds as mystical as reading fortunes in Turkish coffee grounds. In fact, the phenomenon has a scientific basis. Coffee beans contain oils that float on the coffee's surface and create surface tension. When a sugar cube is placed in hot coffee, it releases bubbles as it dissolves. Suspended on the surface, those bubbles act as a barometer.

On the same horizontal plane, when atmospheric pressure is unevenly distributed, air flows from high-pressure areas toward low-pressure ones. Air from higher-pressure regions moves horizontally into surrounding areas, while air above a high-pressure region descends. This happens because atmospheric pressure rises as altitude falls. As air from higher altitudes descends, the pressure it experiences increases, its volume decreases, and its temperature rises (as taught in high school physics, PV/T=C). In the center of a high-pressure area, conditions are unfavorable for cloud and rain formation, typically producing cloudless, sunny days. The reverse also holds true.

Practical Considerations

Doesn't that suddenly make a single cup of coffee seem full of science? You may be tempted to try it at home. Note that bubbles can float on the coffee's surface and work as a barometer only when the coffee oils are right. Instant coffee and pour-over coffee are not the best choices; freshly ground, freshly made hot Americano is the ideal option.

As for the sugar, the book specifically calls for sugar cubes rather than regular granulated sugar. That is because the porous gaps between the particles in a coffee sugar cube make it easier for bubbles to form as it dissolves.

Conclusion

So there you have it — a quick refresher on how atmospheric pressure shapes the weather, straight out of high school geography.

"Right now, I just want to open my phone and check the weather forecast. If it says rain, I'll bring an umbrella — no more taking chances."

Image source: Internet

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