BACKGROUND: The NOAA National Weather Service is introducing storm-based warnings for tornadoes, severe thunderstorms, flash floods and marine hazards that are more geographically specific for these short-duration weather events. Currently, such warnings are issued county wide. Effective October 1, people can receive more specific warnings about upcoming severe weather, even accessing it on cell phones, Blackberries or the navigation systems in their cars. Storm-based warnings provide the public with information about the location of severe weather and the direction in which it is expected to move, but weather doesn't always follow geopolitical boundaries. The new system is designed to provide the most accurate and timely description of what's happening in a specific neighborhood or region.
HOW STORMS DEVELOP: Storm clouds form as moisture evaporates from the earth into the atmosphere, where the droplets congregate and jostle against each other. The air cools off rapidly with altitude and the water vapor condenses into liquid drops, forming clouds. The process continues: more and more water vapor turns into liquid, and the moist air warms up even more and rises higher and higher. The severity of a storm will depend largely on the buoyancy of the rising air within the storm and the structure of the wind within the atmosphere.
WHAT IS DOPPLER RADAR: Doppler radar uses a well-known effect of light called the Doppler shift. Just as a train whistle will sound higher as it approaches a platform and then become lower in pitch as it moves away, light emitted by a moving object is perceived to increase in frequency (a blue shift) if it is moving toward the observer; if the object is moving away from us, it will be shifted toward the red end of the spectrum. Doppler radar sends out radio waves that bounce off objects in the air, such as raindrops or snow crystals, and then measures how much the frequency changes in returning radio waves to better determine wind direction and speed.
WHAT'S THE FORECAST: Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. Humankind has attempted to predict the weather since ancient times. In 650 BC, the Babylonians predicted the weather from cloud patterns. In about 340 BC, Aristotle described weather patterns in Meteorologica. Chinese weather prediction lore extends at least as far back as 300 BC. Ancient weather forecasting methods usually relied observed patterns of events. For example, it might be observed that if the sunset was particularly red, the following day often brought fair weather. This experience accumulated over the generations to produce weather lore. Today, weather forecasts are made by collecting data about the current state of the atmosphere and using computer models of the atmospheric processes to project how the atmosphere will evolve.
The American Meteorological Society and the American Geophysical Union contributed to the information contained in the TV portion of this report.