Weather Whys; Nexrad

This is Weatherwise. A powerful tool will soon be available to meteorologists in the United States and abroad, and it has the potential to revolutionize the forecasting of severe weather. You might have heard it called NEXRAD, but the official name is the WSR-88D. NEXRAD is short for next-generation weather radar, and this advanced Doppler radar system promises many new insights into atmospheric phenomena. NEXRAD uses something called the Doppler effect to get more information about storms than could old-style radar. The effect is similar to what happens when you stand near railroad tracks as a train goes through. You'll notice the pitch of the train whistle appears to get lower after the engine passes. That's because the sound waves essentially bunch up in the area where you're standing ahead of the speeding train. Since the sound waves are packed more closely, there's what's called a frequency shift in the sound. The change makes the sound seem higher pitched than it actually is. Similarly, the electromagnetic waves or radar bounces off a cloud full of raindrops will

come back with a higher frequency if the cloud is moving toward you. The frequency will be lower if the cloud is moving away. In the same fashion, the electromagnetic radar waves being returned from winds moving toward you would be bunched up. Of course, in this case, you can't tell the difference, but a radar unit can. That frequency change is called the Doppler Shift. Doppler radar uses that shift to tell where storm winds are blowing, and with its help, forecasters can see rotation developing high up in a thunderstorm cloud, often a half hour before the rotation turns into a tornado. That helps the local authorities give more timely warnings when severe weather is about to strike. Next-rad itself is essentially Doppler radar combined with computer processing, which puts large amounts of detailed weather information at a meteorologist's fingertips, and that extra information is expected to make a big difference. For WeatherWise, I'm Drew Barlow.