Why Are D.C.'s Official Weather Readings Measured in Virginia? | WAMU 88.5 - American University Radio

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Why Are D.C.'s Official Weather Readings Measured in Virginia?

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Critics say monitoring the weather at Ronald Reagan Washington National Airport is not representative of D.C. as a whole for a number of reasons.
Critics say monitoring the weather at Ronald Reagan Washington National Airport is not representative of D.C. as a whole for a number of reasons.

If you were tuned to this radio station at 4:04 p.m. on June 29, 2012, this is what you would have heard WAMU 88.5 news anchor Pat Brogan say:

A record-high temperature for the D.C. region that stood for almost 80 years was broken today when the mercury reached 104 degrees at Reagan National Airport. The old record of 101 degrees was set in 1934.

Indeed, D.C.’s temperatures were breaking records right and left that day. Though when we say “D.C.’s temperatures,” we’re not actually talking about temperatures in D.C.

No. We're talking about temperatures in Arlington, Virginia.

“Ideally, Washington D.C.’s temperature reading would be taken in Washington, D.C.,” says Washington Post weather editor Jason Samenow. “It wouldn't be surrounded by tarmacs. It wouldn't be adjacent to the river.”

And yet, since 1942, D.C.’s official temperature sensors have been across the Potomac at Ronald Reagan Washington National Airport.

As Samenow explains, “most weather stations across the country are co-located with airports. That’s because aviation needs reliable weather observations for pilots to know what the visibility is, what the cloud ceilings are, to protect against aviation accidents.”

White House weather?

When we met up with Samenow earlier this week, it wasn't at DCA. Instead we picked a spot that’s been proffered as an alternate location for D.C.’s official weather gauge: The White House.

“Robert Leffler, [a] retired National Weather Service climatologist, actually put out a proposal that the official weather-observing station be at the White House,” Samenow recounts. “And that was actually floated around the National Weather Service for a period of time. But it was squashed, I think, because there would be an added cost to having a weather observer at the White House.”

Plus, Samenow says, moving the station could screw up decades of carefully-kept temperature records, “because if you're trying to see whether the climate’s changing over time, you don’t know if it’s due to the fact that the location’s changed, or whether there’s actually a true climate change signal during that time period.”

But still, Samenow acknowledges a number of potential problems with the current site of Washington, D.C.’s weather observations.

First off, DCA has an especially low elevation along the river, and as he explains, “the river can actually influence the temperature at the airport, [since] you have wind from the south coming right up the river. That’s going to influence the temperature because the water temperature of the river is going to influence the air at the airport.”

Additionally, he says, the airport is “in a very urbanized location with a lot of asphalt. You've got the runways there and the tarmac. That’s going to also potentially influence the temperature reading that you're getting at the airport.”

Asphalt as a proxy for asphalt?

And indeed, it’s been shown that temperatures observed at DCA are often among the highest in the Washington metro region. We've seen a number of days where temperatures at the airport were measured to be far higher than they were at many of the National Weather Service’s other observing sites in the region.

Samenow says retired climatologist Robert Leffler has been watching these numbers closely, “and he’s seen that Reagan National Airport is always at the top in terms of the temperature readings across the region, and even sometimes as hot as temperature regions to our south, places like Richmond and Atlanta.”

In fact, Samenow says, on some mornings, “Reagan National… is reading warmer than it is in Atlanta, just because there is all this asphalt surrounding it, [and] there’s a river. So the temperature has a hard time dropping off at night.”

At the same time, he says, “if you're looking for a temperature reading which may be somewhat indicative of what it’s like in downtown Washington, with a lot of concrete and asphalt, Reagan National Airport isn't the worst proxy for that. Whether it’s a good indication of what the entire region’s temperature is like, that’s an entirely different story.”

Now, mind you, it isn't like DCA’s temperature gauge is actually smack-dab in the middle of the tarmac.

Samenow says “it’s on a grassy area adjacent to the tarmac. The temperature reading is shaded, covered… in a shelter so it’s protected from some of the effects that you might have from the asphalt and whatnot. But it’s [still] not an ideal environment for recording temperatures.”

Now, as to how WAMU’s news anchors should proceed with reading the weather, Samenow says “if you're a purist, you want to refer to the location at which the temperature’s taken, which is Reagan National. But… as a proxy, if you want to generalize, we're just talking about across the river here; it’s not a huge distance.

Basically, he says, “you're not committing a crime if you say that the temperature at Reagan National Airport is the temperature in D.C., because most of the time you're going to be pretty close.”

Music: "Sunshine Superman" by Gabor Szabo from Bacchanal


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