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Why do clouds turn green during some storms?
The visible light spectrum covers colors from violet to red. Each color corresponds to a different wavelength, with green sitting roughly in the middle. Blue and violet have shorter wavelengths. Light rays change direction when they hit particles — a process known as scattering. The sky looks blue because air molecules scatter shorter wavelengths more effectively.
Clouds are made of water drops and ice crystals that scatter light from the sun in all directions. It is the multitude of drops and crystals that make a cloud look white during the day. Sometimes only a small amount of light escapes out the bottom, and so cloud bottoms often appear grayish. Continue reading
Category: Meteorology, Phenomena, Severe Weather
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What is the shape of raindrops?
While cartoonists typically draw raindrops like a teardrop or a pear shape, raindrops are not shaped like that.
They are drawn as teardrops to give the image of falling through the atmosphere, which they do. But as they fall, raindrops are flattened and shaped like a hamburger bun by the drag forces of the air they are falling through. Continue reading
How is air quality measured and what are the trends in Wisconsin?
The amount and density of pollutants in the air are converted into an Air Quality Index, or AQI. The Wisconsin Department of Natural Resources’ statewide monitoring network is operated following a federally approved plan. The DNR statewide network includes 30 ozone and 18 fine particle, or PM2.5, monitoring sites. PM2.5 describes particles with diameters that are generally 2.5 micrometers or smaller and thus inhalable.
Under the Clean Air Act, the Environment Protection Agency sets National Ambient Air Quality Standards for pollutants. Continue reading
What are ice balls and how do they form?
If you were lucky enough to be walking along Lake Mendota shoreline at Shorewood Hills and Frautschi Point on March 16, 2026, you might have seen ice balls, or ice eggs, floating in the water. This was a rare occurrence of naturally formed balls of ice that form in cold water.
While they look a little like hail, the formation of ice balls is very different. The freezing temperatures form sheets of ice on the water surface. The wind and the resulting wave action causes the ice sheets to break up and form small pieces of ice and slush. The gentle tossing of the water by a breeze causes the pieces of ice to collide and stick together. Single balls of ice begin to form in the ebb and flow of water and grow as layers of water freeze over the surface of the ice balls. Eventually the wind and water currents move the ice balls to the shoreline where they collect. Continue reading
What is clear air turbulence?
Clear-air turbulence, or CAT, is the turbulent movement of air masses in the absence of any visual clues such as clouds. The atmospheric region most susceptible to CAT is at altitudes of around 23,000 to 39,000 feet. This is the region of jet streams — fast-moving, narrow bands of wind high in the atmosphere that blow from west to east.
Wind shear refers to a sudden change in wind speed or direction across a short distance. When an aircraft encounters wind shear, it may experience abrupt vertical or horizontal movements, resulting in unanticipated changes in altitude or velocity. While wind shear is commonly observed in the vertical dimension, it can also manifest horizontally. Continue reading
