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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 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
Was the February 23 snowstorm in the Northeast really unusual?
The northeast United States experienced a once-in-a-generation storm on Feb. 23-24. It would take too much space to list all the remarkable snowfall records that were set during this event, though mentioning a couple is both irresistible and instructive.
Southeast Massachusetts and most of Rhode Island were hardest hit by both the snow and winds associated with this event. T.F. Green International Airport at Providence, Rhode Island, ended up with 37.9 inches of snow — its all-time two-day and single-day records — and suspended all operations on Feb. 23. Hurricane-force wind gusts were widespread in the region, with Wellfleet, Massachusetts recording a peak gust of 98 mph. Continue reading
Category: Meteorology, Seasons, Severe Weather
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Was 2025 an interesting weather year for Wisconsin?
Wisconsin has interesting weather in EVERY year. 2025 started with extreme cold warnings issued for all Wisconsin counties from Jan. 19 to Jan. 21. Wind chill indices were as low as minus 45. The year also ended with cold temperatures and low wind chills at the end of December.
Severe thunderstorms struck southern Wisconsin during the early morning of April 18, with baseball-size hail falling from New Glarus to Edgerton. Continue reading
Category: History, Phenomena, Severe Weather
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What is the largest snowflake?
An ice crystal can grow if the air around it has a relative humidity near 100%. The ice particle grows by water vapor deposition. Growth by deposition is generally slow. If you find nicely shaped snowflakes, they likely were produced by vapor deposition. A snowflake can be an individual ice crystal or an aggregate of ice crystals.
There are four basic shapes of ice crystals: the hexagonal plate, the needle, the column and the dendrite. The dendrites are hexagonal with elongated branches, or fingers, of ice; they most closely resemble what we think of as snowflakes. The temperature at which the crystal grows determines the shape. Continue reading
