Do you ever feel like the weather is out to get you? All week long, it seems, you sit inside at school while the sun shines outside. Then, as soon as the weekend comes, the sky turns gray. There's rain in the forecast.

In some ways, you may be right. Weekend weather differs from weekday weather in certain places, say researchers who studied more than 40 years of weather data from around the world. They focused on temperature differences between daytime highs and nighttime lows. This difference measurement is called the diurnal temperature range, or DTR.

Part of the study involved 660 weather stations in the continental United States. At more than 230 of these sites, the average DTR for Saturday, Sunday, and Monday was different from the average DTR for Wednesday, Thursday, and Friday, the researchers found. The difference was small—only several tenths of a Celsius degree—but the pattern was striking enough to make the scientists take notice.

In the southwestern U.S., temperature ranges were typically broader on weekends. In the Midwest, weekdays saw larger daily temperature variations.

This sort of weekly rise and fall doesn't line up with any natural cycles, the researchers say. Instead, they blame human activities, possibly air pollution from those activities, for these weather effects. For example, tiny particles in the air could affect the amount of cloud cover, which would in turn affect daily temperatures.

So, tiny windborne particles from California, generated on weekdays, might first affect weather close to home in the southwest, then later influence midwestern weather.

It looks like your weekend weather has a lot do with which way the wind blows and where it comes from.—E. Sohn