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Category Archives: Meteorology
Who or what triggers the decision to sound a tornado siren?
The National Weather Service is responsible for issuing forecasts, watches and warnings for a variety of weather and water hazards. A “warning” is issued when hazardous weather poses an immediate threat to life or property.
A warning can be issued for a variety of hazardous weather, including tornadoes, thunderstorms and flash floods. These threats can form quickly, last a few minutes and impact a small area. Forecasters must rely heavily on observational data from Doppler radar, satellite, and other ground-based equipment and sensors to inform them during the warning process. Continue reading
Category: Meteorology, Severe Weather, Weather Dangers
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What is the tornado scale?
A tornado is a powerful column of winds that rotate around a center of low pressure. The winds inside a tornado spiral inward and upward, often exceeding speeds of 300 mph. We classify the strength of a tornado after trained observers assess the damage it did to the area.
All tornadoes are assigned a single number from the Enhanced Fujita Scale (EF) according to the most intense damage caused by the storm. When tornado-related damage is surveyed, it is compared to a list of damage indicators and degrees of damage to help estimate the range of wind speeds the tornado likely produced. The rating is assigned based on a set of 28 damage indicators, such as barns, schools and trees; the degree of damage to each one is used to determine the EF scale of every tornado. Continue reading
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
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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