Q: I checked my rain gauge after the storm on the Fourth of July, and it said we’d gotten more than 4 inches, but when I checked the paper, it said Manhattan had only gotten 2 inches. How can there be such a big difference?
A: Based on anecdotal reports from Facebook, there were huge differences in the amount of rain that fell in different parts of town early on Independence Day.
Some people said their gauges indicated more than 6 inches, while official reports said it was only 2 inches.
According to the Kansas Weather Data Library, the gauge on campus had 2.07 inches between 7 p.m. July 3 and 7 a.m. July 4. Some places had 3, 3.5 or 3.7 inches for the same period. North of Riley, an official gauge showed 1.8 inches, and near the dam the total was 2.73.
K-State climatologist Mary Knapp said that kind of variance actually isn’t terribly unusual.
“Oh yeah, all it takes is one storm blowing up over an area, and it doesn’t move much,” she said. “When that happens, one spot gets very heavy rains and another doesn’t. You could be literally on the other side of the street and get very different amounts.”
She said such disparities are especially common with “convective” storms.
“That’s where the heating of the day increases the evapotranspiration, so you get these clouds bubbling up over one area,” she said. “If you’re in one area, you might get a bunch of different rain totals.”
Another thing that contributes to apparent differences in precipitation is the type of gauge people use. Different types can give different results. And if people don’t empty them, it can skew results.
She said the weather data library uses CoCoRaHS gauges. CoCoRaHS stands for Community Collaborative Rain, Hail and Snow Network. Knapp said people can join the network and get their own gauge (www.cocorahs.org).
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