The radar unit at the National Weather Service's forecast office in Sterling, Va. (Greg Schoor/National Weather Service)

Why is it when I watch the local weather, the radar is always centered on Leesburg? Is it because of the FAA buildings?

— Andrew Jones,


People often wonder why weather records are centered on airports. Who cares if the high temperature at Dulles Airport was 99 degrees or Reagan National Airport received 8 inches of snow? No one lives at the airport.

True, but weather is vitally important to people inside of airplanes that are about to take off or land. That’s why wind, rain and ice conditions are so carefully monitored at airports. And that’s why the National Weather Service has its Baltimore-Washington forecast office in Sterling, Va., not far from Dulles. Another reason: There are fewer tall buildings in that area, meaning fewer things that could interfere with the mighty WSR-88D.

That stands for “Weather Surveillance Radar, 1988, Doppler.” You may have seen it from West Ox Road. It looks like a massive Titleist waiting for a giant golfer to smack it down the fairway. The huge, white orb is the protective shell for the radar unit that lives inside.

The radar unit itself resembles a satellite dish, said National Weather Service meteorologist Greg Schoor. “This big, massive satellite dish sits on a pedestal,” he explained. The dish “spins around, and a big antenna that hangs on the front side of the dish shoots out an electromagnetic pulse.”

Like a flashlight beam, the pulse is narrower at the source, fanning out and getting weaker the farther it travels from Sterling. It can reach out about 100 nautical miles, Greg said, creating a probing circle 200 miles in diameter. The dish can scan at multiple levels, tilting up its beam to capture more information.

Sterling’s WSR-88D was installed in 1992. There are 122 units located across the United States, positioned so that nearly the entire country is blanketed. They give forecasters a pretty good idea of what’s going on, weatherwise.

“Radar can tell where hydrometeors — that’s a fancy word for raindrops — are and how fast a group of hydrometeors are going,” Greg said.

Like a good therapist, the radar spends as much time listening as it does talking. It analyzes the signals that bounce back, using complex algorithms to determine the location, composition, speed and direction of the things the beam hits, whether they be rain-filled clouds or flocks of birds.

“It’s effectively like taking an MRI or a CAT scan of a storm,” Greg said.

Three of Washington’s four local TV stations also have their own radar units, though they aren’t as sophisticated as those used by the National Weather Service. The radar for WJLA (Channel 7) is in Mitchellville, at Freeway Airport. Thus, the sweeping hand of the radar is centered there when it’s displayed on Channel 7.

WUSA (Channel 9) and WTTG (Channel 5) each have a radar device in College Park, although WUSA’s is broken. WRC (Channel 4) does not have a radar — it uses a feed from the National Weather Service’s Sterling radar. (So, too, does The Washington Post on our Web site.)

All the local stations can switch radars, depending on what their meteorologists are tracking. They can select a Weather Service feed from Pittsburgh or feeds from Dover Air Force Base or BWI. They can even combine multiple feeds for a big-picture overview.

“If I have a [storm] cell that is in Cumberland, I may get a better picture from Pittsburgh radar than from Sterling radar,” said WUSA’s Howard Bernstein. “We serve such a large area: Eastern Maryland, southern Pennsylvania, down to Fredericksburg, over to the Northern Neck of Virginia. Even parts of the Eastern Shore. A lot of things are in play.”

Of course, something else is in play, too: bragging rights and ratings. In the hypercompetitive world of local TV news, stations trumpet their branded super Doppler radar, even if they also use the government’s radar.

It’s a reflection of how important weather is to TV news and the viewers who watch it.

Said Howard: “You can avoid news. You can avoid sports. . . . Unless you’re living underground and have a food and energy supply and a life-support system, you cannot avoid the weather.”

And weather can’t avoid the unblinking, all-seeing eye of radar.

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