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Why Your Car Dashboard Says It's a Lot Hotter Than It Really Is

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When you first turn on your car in the middle of a sunny day, chances are your dashboard probably says it’s quite hot out. Like, a lot hotter than it feels. There’s a reason why car thermometers don’t always seem accurate, according to atmospheric scientist Greg Porter at The Washington Post.

Your dashboard temperature reading actually comes from something called a thermistor, which is similar to a thermometer but instead of mercury, it uses electrical current to measure changes in temperature. (Remember that temperature is an indication of how fast or slow gas molecules in the air are moving around. The higher the reading, the greater the molecules' kinetic energy.) In a car, that thermistor is located just behind the grill in the front of the car. Therein lies the problem: Your car's temperature readings come from an unusually hot location.

Asphalt roads get really, really hot in warm weather (enough so that cities become significantly hotter than their greener surroundings in the summer), so a temperature reading taken just above the surface of the road isn’t going to be super accurate. Heat radiates up from the road—as you can see on particularly hot days when the highway starts to look shimmery—and the thermistor in your car picks up that excess heat. It’s like measuring the temperature of a large room by sticking the thermometer an inch away from the fireplace.

That doesn’t mean your dashboard temperature readings are useless. When it’s not as hot out, there isn’t much interference from heat rising off the road. It’s also more effective when you’re moving—if you’re traveling down the highway, it will pick up less heat radiation from the road than if you were sitting in a parked car. However, Porter warns, the thermistor isn’t sensitive enough to distinguish between one-degree differences, which can be dangerous if you’re driving in the winter and need to know if temperatures have hit freezing or are floating just above.

In short, as nice as it is to know how temperatures are changing from one destination on your road trip to another, take that dashboard number with a grain of (road) salt.

[h/t The Washington Post]

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Weather Watch
Why Does the Sky Look Green Before a Tornado?
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A common bit of folklore from tornado-prone parts of the U.S. says that when the skies start taking on an emerald hue, it's time to run inside. But why do tornadoes tend to spawn green skies in the first place? As SciShow's Michael Aranda explains, the answer has to do with the way water droplets reflect the colors of the light spectrum.

During the day, the sky is usually blue because the shorter, bluer end of the light spectrum bounces off air molecules better than than redder, longer-wavelength light. Conditions change during the sunset (and sunrise), when sunlight has to travel through more air, and when storms are forming, which means there are more water droplets around.

Tornadoes forming later in the day, around sunset, do a great job of reflecting the green part of the light spectrum that's usually hidden in a sunset because of the water droplets in the clouds, which bounce green light into our eyes. But that doesn't necessarily mean a twister is coming—it could just mean a lot of rain is in the forecast. Either way, heading inside is probably a good idea.

For the full details on how water and light conspire to turn the sky green before a storm, check out the SciShow video below.

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Weather Watch
New Contest Will Give Kids the Chance to Become Weather Channel Meteorologists for a Day
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Not every kid dreams of being an on-air meteorologist, but for young ‘uns obsessed with storm forecasts and local weather reports, a new contest presents a unique opportunity to live out their dreams. The Mini Meteorologist Contest, sponsored by Lands’ End, will give four kids a chance to present a weather report on The Weather Channel this summer.

The nationwide contest is open to future meteorologists in the U.S. and Canada ages 6 to 16. To enter, they just have to write an essay between 50 and 500 words long on why they love learning about science and weather and why they’d like to be a meteorologist for a day. Four winners will receive a trip for them and their parents to The Weather Channel’s headquarters in Atlanta. They’ll have the opportunity to report the weather for the show on July 12, which happens to be National Summer Learning Day.

The essays will be judged based in equal parts on creativity, grammar, and the entrant’s love of meteorology. The only rules for the essays are that they can’t mention any products or brands other than Lands’ End or The Weather Channel (so no essays about how L.L. Bean inspired your love of cloud formations, kids) and has to be the child’s original work. Kids who are chosen as semi-finalists will have their on-air presentation skills judged in a Skype interview.

Should they win, they’ll get an inclusive trip to Atlanta with media training, a tour of The Weather Channel headquarters, and a $500 Lands’ End gift card to get just the right weather-reporting wardrobe.

The deadline for entering is May 21. Essays can be submitted here.

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