By: John Shepler
The Doppler radar for the National Weather Service needs to be recalibrated twice a year. It's not to compensate for changes in the electronic circuitry. It's because the leaves fall off the trees in autumn and new ones reappear in late spring. The ultrasensitive radar sees this as a change in the terrain and loses track of what is permanent and what is moving.
On the radar screen inside the Chicago office, 100 feet below the 28 foot dome housing the Doppler radar's antenna, the meteorologists on duty scan patterns of reds and greens, looking for shifts in the wind. This is what differentiates Doppler from other types of radar. It not only tells you how far away things are but also how fast they are moving. The green areas represent winds blowing toward the radar. The reds are winds blowing away. The stronger the colors, the faster the winds are moving.
For most of the year, the radar tells forecasters exactly how fast the winds aloft are moving. But twice a year this part of the radar also goes out of calibration. In the spring, when birds migrate north, the south to north winds appear to be blowing faster than they really are. It's because the birds' velocity is added to that of the wind. In the fall, the north to south winds are equally out of calibration. I stare at the screen in amazement that flocks of birds miles or dozens of miles away can affect what shows up on weather radar screens. Yet, this seeming oversensitivity in the equipment becomes well worth the occasional nuisance when violent storms are in the area. Every shift in wind patterns can be critical to aircraft landing at nearby O'Hare International Airport. Those colored patterns could also be locating the characteristic hooked signature of a tornado forming overhead.
This past weekend, my wife Barbara and I were invited to visit the National Weather Service office that serves our area from Romeoville, IL, in the flat fields southwest of Chicago. We got our invitation over our personal weather radio from a voice with a curiously electronic sound. We headed that way, hoping to find out who that odd announcer was and why he seemed to be on at all hours of the day and night.
This was the first ever open house of the Chicago weather forecast office in their state of the art facilities in Romeoville. Chicago has had a forecast office since 1894, shortly after the weather service transferred from the Army Signal Corps to the Department of Agriculture. In 1940, weather forecasting responsibility transferred again to the Department of Commerce and is now part of NOAA, the National Oceanic and Atmospheric Administration. The Chicago office started at the Post Office downtown, moved to Rosemont to be near O'Hare Airport, and then moved again next to Lewis University Airport near Romeoville in 1991, when that location was picked as the best spot for the $2 million Nexrad Doppler Radar.
Our tour began with an explanation of how the NOAA weather radio works and the important features that have been added just recently. For instance, did you know that a digital coding called SAME (Specific Area Message Encoding) will turn on weather radios only for the locations you have programmed? If your radio has that feature, you can set your radio to wake you up only if there is a watch or warning for your specific county. This technology is so useful that has been adopted for the country's new national Emergency Alert System.
We met our mystery announcer in the next room. He's known affectionately as "Iron Mike," and he is indeed a computerized voice. Mike is what's known as a text to voice translator. As the meteorologists develop a new forecast, they type it into their computers and it becomes available to airports, police stations, radio and TV stations, newspapers and Iron Mike. Mike instantly converts the text of the forecast or weather data into spoken words that go out phone wires to a weather radio transmitter within 40 miles of you. Previously, meteorologists had to take extra time to go into a little studio and record tapes for the broadcasts. Mike does that for them now, saving 10 or 20 minutes that could be critical in a rapidly developing emergency.
At National Weather Service offices such as Romeoville, the traditional weather forecasting instruments still have an important role. While a geostationary satellite hovers overhead sending moving pictures of the clouds, the familiar anemometer cups spin to measure wind just outside the building. A weather vane swings back and forth to sense the wind's direction, and a metal rain bucket gathers precipitation and measures it to within a hundredth of an inch. They still use weather balloons to carry instruments with radio transmitters, known as radiosondes, up through the atmosphere. We got to touch one, and oddly enough they feel "gooey" to the touch. The special material expands as the balloon rises until it finally bursts at about 35,000 ft. and the radiosonde parachutes to earth. Oh, yes, these balloons get so large and under certain conditions reflect sunlight so well that even today they are still routinely reported as UFOs. Not everything in the weather service has changed.
Books of Interest:
The Weather Book by Jack Williams, USA Today. The best, most readable and visually stimulating guide to our nation's weather--featuring the full-color graphics of the most popular section of America's most popular newspaper.
Weather: An Explore Your World Handbook by H. Michael Mogil, Discovery Channel. This new book was created by the Discovery Channel to help you understand how our weather works in a clear and easy to follow format. It contains over 300 photographs that explain the inner workings of hurricanes, tornadoes, thunderstorms, weather fronts and more. The up to date information is provided by professional meteorologists.
The Weather Tracker's Kit by Gregory C. Aaron. Budding meteorologists will enjoy the giant cloud chart plus a functional weather station that includes a wind direction and speed indicator, a rain gauge, a thermometer, and a wind-chill chart. An illustrated handbook teaches all about weather lore.
Also visit these related sites:
NOAA Weather Radio - How it works, where to get a radio and a listing of the channels available in your area. Now, you can listen to and comment on the new voices proposed to replace Igor, the mechanical voice of NOAA Weather Radio.
NOAA - Home Page of the National Oceanic and Atmospheric Administration of the Department of Commerce, which operates the National Weather Service, National Ocean Service and other important agencies.
Copyright 1999 - 2018 by John E. Shepler. Contact me at: John (at) JohnShepler.com
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First Published: October 3, 1999 as part of A Positive Light