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Category Archives: Meteorology
What causes tornados and do they have a lifecycle?
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 don’t know if a particular storm will produce a tornado but we do know the necessary conditions needed for tornado formation.
The required conditions for a thunderstorm to produce a tornado are warm humid air near the surface with cold dry air above. These conditions make the atmosphere very unstable, in the sense that once air near the ground is forced upward, it moves upward quickly and forms a storm. Severe thunderstorm conditions also include a layer of hot dry air between the warm humid air near the ground and the cool dry air aloft. This hot layer acts as a lid that allows the sun to further heat the warm humid air, making the atmosphere even more unstable. Continue reading
Category: Meteorology, Phenomena, Severe Weather
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How do satellites help forecast the weather?
Satellite data help forecast the weather in two ways: expert forecasters interpret the satellite images and numerical weather-prediction models assimilate the data they collect. Image analysis plays an important role in short-term forecasts, those that predict the weather 1 to 3 hours into the future, while numerical weather predictions are more useful in 12-hour to 3-day forecasts.
While weather forecasters routinely analyze current satellite observations, most data never reach forecasters’ eyes. Most satellite observations are assimilated into numerical weather-prediction models. Today’s weather forecast models rely on satellite data to make accurate weather predictions. These satellite observations include the vertical distribution of temperature and humidity, cloud distributions, land and sea surface temperatures, location of volcanic ash, fires, and wind speeds and directions. Continue reading
What is vapor pressure?
Weather reports often include the dew point temperature and the relative humidity. These are just two of several ways to express the amount of water vapor in the atmosphere. Vapor pressure is another way. Each method has advantages and disadvantages.
Gas molecules exert a pressure when they collide with objects. The atmosphere is a mixture of gas molecules and each type of gas makes up a part of the total atmospheric pressure. The pressure the water molecules exert is another useful method of representing the amount of water vapor in the atmosphere. The pressure caused by these water vapor molecules is called the vapor pressure. Atmospheric vapor pressure is expressed in millibars (mb). Continue reading
What are radiosondes?
Radiosondes are instrument packages that measure the vertical profiles of air temperature, relative humidity, and pressure from the ground all the way up to about 19 miles. These radio-equipped meteorological instrument packages are carried aloft by a helium-filled “weather balloon.” … Continue reading
Why does the severe weather threat increase as spring and summer approach?
As the threat of winter snows recedes across the country, it is replaced by the threat of severe weather (i.e. thunderstorms with hail, damaging winds and tornadoes).
The severe weather season, though broadly spanning March through August across the United States, is actually quite regional. It begins in March in the southern states, moves to the southern Plains during April and May, and then further north toward the Great Lakes states during the summer. Continue reading
Category: Meteorology, Seasons, Severe Weather
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