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Memphis Flyer Rolling Thunder

Weather radar comes to the Internet in a big way.

By Bill Steinberg

MAY 8, 2000:  In 1986, before the M-word (millennium) was uttered, no one could really comprehend the technological wonders that were just around the corner.

Only a minority of people, mostly at their workplace, had access to early-generation personal computers.

The Internet was in its theoretical infancy. Few people recognized the term "on-line." Even the computer literate could not fully conceive how the Internet would change the fabric of our daily lives.

Concurrently in 1986, Agricenter International, all shiny and new, opened the doors of its spacious exhibition facility at Shelby Farms.

That same year, the National Weather Service (NWS), with offices in the Agricenter, erected its first modern radar tower in Memphis -- representing a giant leap ahead in technology from the forecasting abilities of meteorological satellites that were introduced in the 1960s.

The 100-foot tower with its distinctive white radome at the top -- resembling a futuristic device from an H.G. Wells novel -- is positioned just a stone's throw from the facility's main entrance. The site it stands on is among the highest elevations in Shelby County.

Now, in the year 2000, high-speed Internet capability, coupled with the abundance of relatively inexpensive and high-powered PCs, is changing the way America does business and, perhaps more importantly, how information is rapidly disseminated -- including weather radar information.

The National Weather Service still maintains a presence at the Agricenter. But the government agency, acting on a mandate from Congress, eventually built its first Doppler facility in Shelby County, a more powerful NEXRAD radar facility located at Millington.

When the agency abandoned its initial weather radar tower in the mid-'90s, the NWS sold the landmark facility to the Agricenter for $1 to avoid the financial burden of ongoing maintenance, liability management, and eventual demolition expenses.

Veteran FOX 13 meteorologist Jim Jaggers first learned of the tower transaction and persuaded the new management of WHBQ-TV to lease the radar facility from the Agricenter. After refurbishing the radome's surface, along with upgrading to Doppler radar capability, the new Channel 13 radar tower made its debut in February 1997.

"It was a case of being in the right place at the right time," confesses Jaggers. "We were able to improve both the graphics quality and geographical reliability of our weather reports, particularly during periods of severe weather."

Jaggers also recognized that the acquisition would enhance the viability of FOX 13's fledgling Web site (www.fox13whbq.com). Now, the constantly updated, colorful Doppler Weather Radar images are just a few mouse clicks away.

Jaggers has done his part to help Internet weather radar blossom into the mainstream of Memphis' day-to-day life.

Everyone knows what a radar display of an approaching storm front looks like -- but few have ever seen the inner sanctum of an actual Doppler weather radar tower.

The base of the tower resembles a concrete bunker. It is far more spacious than necessary for the tall and slender stack of computer equipment running inside the radar tower. Jaggers explains that the NWS did in fact use the room for storage during the facility's original tenure. (A second unopened door leads to an additional storage room where BellSouth Mobility houses the equipment for its cell phone tower apparatus.)

Climbing up a short stairway to the ceiling, Jaggers confidently unlatches and flings open a trap door that leads onto the roof of the base structure.

"The diesel power generator below is designed to kick on when and if the MLGW electrical system temporarily fails during a storm, " Jaggers explains.

Looking upward through the 100-foot metal framework of grated steps and beams, the structure -- the height of a 12-story building -- actually looks much taller than it really is.

Jaggers' perfectly combed hair flails in every direction when he steps outside and begins to climb the series of ladders reaching to the top. He is obviously proud of his domain. The view of Shelby County's spring greenery is both expansive and majestic, particularly when one looks back toward the city.

The sightseeing phase of the ascent comes to a halt as the meteorologist reaches the bottom of the radome. Jaggers unlatches a second trap door which opens sideways and upwards like a folding accordion.

The sunlight filtering through the exterior of the bubble-shaped white translucent radome casts a surrealistic hue on the vast, quiet machinery. The noise of the wind is no longer a factor.

"The radome," Jaggers continues, "serves the function of efficiently shedding rain during a storm, which in turn, improves the Doppler radar signal."

Inside, the massive rotating radar cone, 14 feet in diameter, is finally revealed. It lumbers around inside the radome, like a giant silent grist mill, making one complete 360-degree sweep per minute. Jaggers and his visitor are forced to duck back down the steps through the opening to allow the rotating cone to pass periodically over the opening of the trap door.

The huge cone both transmits and receives the Doppler weather radar signal, acting in part like a huge ear. A specialized software program called IRIS (Internet Radar Image Server) continuously captures the completed radar images and makes them available on the station's Web site.

Doppler radar, with its integration or accumulation display function, makes it easy to accurately calculate the amount of rainfall per hour for any given area by its continuously sweeping signal.

But perhaps the most important tool for weather professionals is the Doppler radar signal's ability to yield precious information about when winds going in opposite directions may be violently colliding, according to soft-spoken John White, warning coordination meteorologist for the NWS in Memphis.

Doppler radar does this by measuring the "radial velocity" of the storm movement. Dangerous situations are signalled by the human recognition of a "tornado vortex signature" in a Doppler display that is basically unintelligible by a non-professional.

White likens the process to focusing a multitude of police radar guns on the raindrops, allowing meteorologists to better understand the capability of the winds and their rotation inside the storm.

There are computer programs that may eventually make the same tornado warning call from the data. But among the pros, tornado vortex signature recognition is still considered to be primarily a human art. Waiting for computer models to react could cost too many lives, White stresses.

The peak occurrence for tornadoes in the Mid-South is usually between March and May. Local residents may recall that devastating winter tornados have struck the area in recent years as well.

Unfortunately, not all severe weather can be predicted ahead of time. Under certain circumstances, a severe weather cell could develop before a watch period is issued from the centrally based NWS Storm Prediction Center in Norman, Oklahoma.

Severe weather warnings, which require immediate defensive action, are only issued on a localized basis throughout the country.

"The best warning is no good if people don't get it in time," White says.

White enjoys explaining how storms and violent weather patterns develop in terms a lay person can understand.

"First you have to have fuel -- that's warm, moist air," White explains. "Secondly, the fuel must be lifted, and that comes from the intrusion of a cold front."

The dense cold air wedges underneath the warmer air, forcing it higher into the atmosphere.

Next comes the cooling process, or as White more accurately describes it, "the release of the latent heat of condensation." As the moist air rises, it expands and cools, condensing out the water droplets that form the rain.

The third critical element for a severe storm is a strong jet stream. Sunlight shining its warm rays on top of the storm clouds helps fuel the storm engine, as well.

Looking at radar displays, a lay person could easily make the false assumption that storm clouds of various heights are straight up and down, or vertically aligned, to the ground.

"If the ground-level winds are 20 mph in a severe storm event, when the jet stream high above is moving 100 mph in the same direction, then the storm front will actually be tilted forward as it moves along," White explains. This tilt keeps the storm from collapsing upon itself like an isolated summer thunderstorm. It also allows the fueling process to be constantly replenished, sometimes building its energy up to violent proportions. When only two of the three necessary factors occur, severe weather is unlikely.

White stresses that flooding is actually the number-one killer related to severe weather.

The heavy rains from strong, slow moving thunderstorms are commonplace in the Mid-South. In the last 11 years there have been about 50 storms coming through Memphis where the official accumulation at Memphis International Airport measured between 2 to 4 1/2 inches.

Storms with less than 2 inches of rainfall can cause flooding as well, if the rainfall comes down rapidly enough, according to White.

Progressing down the list of severe weather killers, White clarifies that lightning actually causes more deaths than tornadoes.

While the most severe tornadoes typically occur in Texas and Oklahoma, the so-called "Tornado Alley," the Mid-South actually sustains more tornado-related fatalities. That's because the population density is lower in the Southwest, and the flat terrain without trees makes an approaching funnel cloud easier to see and track.

In contrast, storms in our area are generally more moist and less well-defined. They are frequently wrapped in haze, and funnel clouds they ultimately produce may be cloaked by the heavy rains surrounding them.

Dale Dockus, meteorologist for Fed Ex at Memphis International Airport, is responsible for the ground forecasts for 160 cities in North America. He also served as one of the first on-air personalities on the Weather Channel in the mid-1980s.

The affable weather professional explodes the myth that the ever-changeable Memphis weather is hard to predict. He explains that in the 10 years he has been forecasting weather for FedEx, the near-time Memphis forecast has been easier to determine than most cities.

"In contrast to Memphis, Portland, Maine, with the water to the east and the hills to the west is an example of a much more challenging forecast," Dockus says. "Wind changes [from those elements] can affect the whole weather pattern in short order."

He further explains that when local forecasts turn out to be inaccurate, it is usually due to cloud cover coming into the region earlier than expected.

Acknowledging the explosion of weather-related Web sites, Dockus stresses that it is critical that users of Internet weather radar understand the timeliness of the images they view -- the fresher the images are, the better.

"Within the meteorological community, Zulu Time is the standard," Dockus advises. While not all Internet weather radar providers use this professional convention, it is helpful to understand that Z time simply corresponds to Greenwich (England) Mean Time.

Depending upon the time of year, Z time is either five or six hours ahead of our Central Time Zone. Currently, with Daylight Savings Time, the differential is five hours.

Dockus strongly advises Internet users to locate the time stamp feature on weather radar displays and to learn the translations when necessary.

The competitive landscape of Internet weather radar may soon undergo a dramatic shake-up.

The undisputed champion of weather radars, the NWS NEXRAD system at Millington, along with its sister facilities throughout the nation, may soon provide their constantly updated real-time images to Internet users free of charge.

Currently, the NWS has exclusive contracts to sell its proprietary NEXRAD images to four separate third-party distributors, who in turn market the images to end-users like the local TV stations. But the current contract expires within the next year, and it is not likely to be renewed in its current form, according to White.

He is optimistic that, in the quest to better fulfill the NWS mission to protect property and life, the cutting-edge NEXRAD radar images will ultimately go public, likely appearing as a series of links on the NWS Web site.

Unlike the original Doppler weather radar tower at the Agricenter, which takes one minute to complete a full rotation and measures atmospheric conditions at a single virtually-level elevation, the NEXRAD system takes five to six minutes to make a full cycle. The extra time is needed to map a variety of atmospheric elevations varying from .5 to 20 degrees above the horizontal plane. The process generates an extensive computer database capable of creating 300 different meteorological products.

It is not enough to know exactly where severe weather is occurring at any given moment. Where it came from and what direction it is heading are two critical questions that are best answered by viewing radar loops, or time-lapse animations of a series of radar pictures. National weather Web sites mentioned above do an excellent job of combining recent radar "snapshots" with the option of linking to a radar loop.

Most national providers update their radar images only twice an hour, so the image viewed on their Internet links could be somewhat stale or outdated, compared to the constantly updated local images found on the local Web sites.

Nimble Websurfers with an avid interest in tracking severe weather shouldn't find it difficult to assemble a list of favorite links to accomplish that task.

What's Out There

There are several national radar displays with regional and/or local displays (including time-lapse animations or radar loops) that do not require paid subscriptions. These five providers are sources for such sites as CNN, Yahoo, and Lycos:

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