Stories tagged weather


It's cold this morning. Maybe the coldest morning of the season so far? Luckily, there's also a lot of sunshine, and almost no wind.

If it were windy, you'd hear the weather forecasters talking a lot not only about the air temperature (-6 degrees when I left the house), but also about the "wind chill." Wind chill is a way to describe how quickly heat is transferred from your body to the atmosphere when it's both cold and windy outside. As wind increases, more heat is drawn from your body, decreasing your skin temperature and eventually your internal body temperature. Wind chill makes it feel much colder than it actually is.

Last year, I overheard a woman in the Science Museum parking garage elevator talking about how she parks her car in a sheltered area to protect it from wind chill. She was worried that, if she left it in a more exposed area, it wouldn't start. I can't say anything about the state of her car battery, or condensation on her distributor, but I can say that wind chill has very little impact on cars or any other inanimate objects: wind will shorten the time it takes for an object to cool to the temperature of the surrounding air, but it won't get any colder than that no matter how much wind there is.

For humans and animals, though, wind chill affects how quickly hypothermia and frostbite can occur. Hypothermia is a condition in which core body temperature has fallen to the point where normal muscle and brain functions are interrupted. (Thor did a post about hypothermia a few weeks ago.) Frostnip/frostbite are conditions in which body tissues freeze. Knowing the wind chill helps us make decisions to avoid these and other cold weather dangers.

She's got the right idea: Bundle up! (Photo by Yann Richie)
She's got the right idea: Bundle up! (Photo by Yann Richie)

The best thing to do when there's a significant wind chill is to stay inside. But you can't stay at home on the sofa all winter. So what can you do? Dress right when you go outside. That means wearing several layers of loose-fitting, lightweight, warm clothing. (Trapped air between the layers will insulate you and keep you warm.) Stay dry. (Remove layers if need be to avoid sweating and later being wet and cold.) Wear a tightly woven, water repellent, hooded top layer. Cover your mouth to protect your lungs from the cold. Mittens, which allow your fingers to share warmth, are better than gloves. And your mom was right: wear a hat! Half your body heat can be lost from your head.


Snow chance: Using data collected over the past 30 years, here are the statistical probablities of having a white Christmas in various parts of the United States.

Will Bing Crosby be singing the blues this year?

He, along with anyone else hoping for a White Christmas, might want to check out this probability map for the chances of having a white Christmas in the United States. As you can see, Minnesota and the upper Midwest are among the prime locations to have a white Christmas.

U.S. weather records averaged over a 30-year period show that only five places with long-term weather records are practically guaranteed to have a white Christmas. They are Marquette and Sault Ste Marie in Michigan, Hibbing and International Falls in Minnesota, and Stampede Pass in Washington.

As the map shows, wide areas of northern Minnesota and Wisconsin, much of Michigan's Upper Peninsula, and western mountains including the Cascades of Washington and Oregon, California's Sierra, and the Rockies from Montana and Idaho south into southern Colorado have a better than 90% chance of snow on the ground at Christmas.

Of course, from year to year the weather varies. There’s never a guarantee of a having a white Christmas. How important is it to you to have a snow during the holidays?


Roger Ledding, former chief of the Minnesota State Patrol, was on WCCO radio this morning, talking about the high number of traffic accidents during today's am rush hour.

No snow, no ice, so what's the problem?

Well, it's been very dry in the Twin Cities lately. A fine spray of oil from cars routinely covers road surfaces. In very dry weather, that oil can build up. When rain begins to fall, it mixes with the oil and the road surface becomes extremely slippery. It can take a few hours for additional rain to break down and wash away the mess.

Also, this morning's wasn't a gentle, soaking rain, but a downpour. That left standing water on roadways. Drivers traveling too fast found themselves hydroplaning--sliding on a thin film of water, unable to stop or steer.

It's been unseasonably warm, for sure, and I wasn't thinking about hazardous driving conditions on my way in to work this morning. But I will be on the way home...

The Minnesota Daily is featuring stories about how climate change could affect Minnesota's north woods. The speakers featured in the article talked with a crowd of over 100 here at the Science Museum of Minnesota last night.


Storm chasers know that puffy cumulus clouds often cause sudden rainstorms, while storms associated with stratus clouds form more slowly. Now physicists at England’s Open University have finally found an explanation.

They propose that neighboring water droplets in a stable stratus cloud don’t crash into each other because they’re all moving at about the same speed. But fast-forming, turbulent cumulous clouds contain water droplets moving at many different speeds. They crash into each other and form larger drops. As the turbulence grows, the drops grow quickly and fall as rain within a few minutes.

Cumulous cloud: These puffy clouds are associated with sudden rainstorms. Scientists are beginning to understand why.
Cumulous cloud: These puffy clouds are associated with sudden rainstorms. Scientists are beginning to understand why.

Sun and rain
Ever noticed the bright, moving lines on the bottom of a stream, bathtub, or swimming pool? They’re called caustics, and they’re caused when ripples on the water’s surface focus sunlight. (Caustics form whenever light rays are bent by a curved surface or object and then projected onto another surface.

Caustics have a characteristic shape. Physicists can graph the phenomenon mathematically, and the graph also describes other phenomena, such as particle motion or the movement of raindrops within a cumulus cloud.

Caustics: What do the rippling patterns on the bottom of a swimming pool and cumulous clouds have in common? (Photo by R. Motti)
Caustics: What do the rippling patterns on the bottom of a swimming pool and cumulous clouds have in common? (Photo by R. Motti)

Atmosphere to outer space
The researchers say their finding won’t have any impact on weather forecasting. But particle collisions in turbulent gases must have been involved in planet formation. Perhaps the same theory can be applied?

If you're at the museum on Saturday afternoon (11/18), the MakeIt team can help you play with caustics. Does bending mylar in a different direction produce a new pattern? Does using a different color flashlight or a brighter or dimmer light affect the design?

You can also play with caustics at home.

NASA scientists spent a month flying a sensor-packed airplane into storms brewing off the western coast of Africa. Data collected from these missions might someday allow better storm prediction and forecasting, and will definitely contribute to our knowledge of how hurricanes form and sustain themselves.


There's been a rash of cool weather sites written up in the Twin Cities newspapers and other media lately.

Here are just a few:

Skeetobiteweather is one of the most popular hurricane sites run by amateurs. Jonathon Grant, of Lakeland, Florida, runs it. He says the site gets 1.8 million page views a week, and you can plug in your zip code and get a prediction of wind forces for your block, hour-by-hour, before a hurricane hits. (Not even the National Weather Service does that.) And pretty soon, you'll be able to enter your exact address.

Mark Sudduth, of Wilmington, North Carolina, runs HurricaneTrack and HurricaneLiveNet. He deploys several battery-powered, waterproof cameras at the exact points where hurricanes are expected to hit. He also collects weather data to accompany the live, streaming video.

Jesse Bass, of Hampton Roads, Virginia, is a weather chaser who posts photos and commentary on his website, VAStormPhoto.

HurricaneCity, despite its name, is one of the more comprehensive severe weather sites. Jim Williams, of Delray Beach, Florida, focuses on the city being hit, and you can see all live, streaming radio stations or TV from the site. He also has a towercam on his roof, which captured images from Hurricane Wilma last year, and he hosts "The Hurricane Warning Show" from his living room.

Mike Watkins, of Coconut Creek, Florida, covers Atlantic hurricane action on TropicalUpdate. And if there's no news on the hurricane front, he hosts an Internet radio show where he interviews the "celebrities" of the weather world--guys like Max Mayfield, of the National Hurricane Center, or William Gray, the Colorado State University professor who's known for his hurricane season forecasts.

A new study found a link between human use of fossil fuels and an increase in the severity of hurricanes. The burning of fossil fuels has increased the level of greenhouse gases in the atmosphere, which has led to the warming of oceans in regions where hurricanes develop. The warmer the ocean water, the more severe the hurricane.


Sunbathers: Soaking up the sun in the California desert. Courtesy Mark Ryan.
Sunbathers: Soaking up the sun in the California desert. Courtesy Mark Ryan.

Here’s a question for the start of summer: why does exposure to the sun darken our skin but lighten our hair?

First let’s take a look at our skin. Human skin is the body’s largest organ, and acts as a barrier between our inner organs and the outside world. It’s made up of essentially two parts the epidermis and the dermis. The epidermis is the outer section and is comprised of a layer of living cells, topped by a layer of dead cells. The dead cells are the skin we see.

Even though the upper epidermis is just a lot of dead cells, it contains keratin, a tough protein that also makes up our hair and fingernails, Keratin is thicker on the bottoms of our feet and the palms of our hands for added protection against abrasions and other intrusions from the outside world.

Inside the dermis is where all the skin’s functioning equipment is located, These include nerves, sweat glands, hair follicles, blood vessels and special cells called melanocytes, which produce melanin, the material responsible for skin pigmentation, hair and eye color. Most humans have about the same amount of melanocytes, some just produce more melanin than others. Albinos, however, produce no melanin at all.

When our skin gets exposed to sunlight (particularly ultraviolet rays) melanocytes begin producing melanin to help protect the dermis, and keep the skin cells from getting fried. The melanin acts as an absorbing agent. So over time, as exposure to the sun continues, more melanin is produced and subsequently the skin becomes darker.

The hair is a different story. Hair color is also determined by melanin, but hair cells are dead, so sunlight doesn’t initiate melanin production but rather begins to break down the melanin already in the hair, and the hair’s color begins to fade or lighten.

Sunglasses may not be so cool: Courtesy Mark Ryan
Sunglasses may not be so cool: Courtesy Mark Ryan

I thought this last part was strange. The pituitary gland is tied to your optic nerve and is sensitive to sunlight. When light enters your eyes, it triggers your pituitary gland to produce a melanocyte-stimulating hormone (MSH) that activates your melanocytes to produce melanin. This means that wearing sunglasses can actually cause sunburn.

UK doctors have warned mobile phone users of the risks associated with mobile phone usage during thunderstorms. Metal found in mobile phones is able to send lightening currents directly into your body-possibly creating lots of damage!