The debate has raged for decades: does it make sense to observe Washington, D.C.’s weather in Arlington, Virginia at Reagan National Airport (DCA)?
Temperatures measured at DCA are often among the highest, if not the highest in the entire metro region. And snowfall measurements often are among the lowest.
Robert Leffler, a retired climatologist for the National Weather Service (NWS) and co-author of the 1981 journal article “Unrepresentative Temperatures at a First Order Meteorological Station: Washington National Airport,” has long tried to build the case for identifying a different observing site.
“[DCA temperatures] are unrepresentative of where most of your readers and the TV listening audience live, work, play, and grow their food. ” he wrote to me in an email.
He added: “How many readers live within 100 feet of the Potomac River on airport runways at sea level? None I know of.”
Leffler pointed out a number of recent days during which DCA’s temperatures were higher than 48 published NWS observing sites in the region. As one example he noted, on July 28 DCA had a high of 97 and a low of 72, whereas the 48 other sites averaged together (from eastern West Virginia to southern Maryland) had a high of 88 and low of 64.
Why is DCA so warm? The airport sits at a low elevation, next to a river and in the midst of urbanized northern Virginia - all of which tend to increase its temperature.
Most suburban locations are cooler - as elevations tend to rise away from the river and the concentration of heat-absorbing infrastructure decreases.
Mark Richards, a senior weather observer at DCA, agrees the airport’s weather readings are a poor indicator of conditions in the suburbs, but argues the airport is a fine location for measuring the city’s temperature.
“I think we provide a very reliable, accurate reading of metropolitan, downtown Washington temperature,” he said.
Leffler said “600 F jet exhaust, miles of tarmac...likely exacerbate the situation [at DCA].”
Blogger Anthony Watts leveled similar criticism: “The ASOS weather station at Reagan National Airport is right on the asphalt. That makes it the worst of the worst when it comes to station siting.”
But Richards dismissed such criticism. He said, in reality, DCA’s temperature sensor, has long been sited on a grassy surface and sheltered.
“We do a weekly comparison with a digital thermometer on the roof [of the airport] in a shaded area and they’re always comparable,” he said. “[Our] system has safeguards built in to make sure we’re not measuring some jet blast or something out of the ordinary - it’s as accurate it can be.”
NWS Science Operations Officer from its Sterling, Va. office (serving the Washington and Baltimore region), Steve Zubrick, backed Richards in defending the legitimacy of DCA’s temperatures:
In an email to me, Zubrick wrote: “Our equipment there is calibrated and checked quarterly for accuracy by NWS technicians and reports 24/7. It is sited properly by the NWS policy that governs proper siting of NWS observation equipment.”
Should a new “official” observing location be selected?
Clearly, the scientific value of DCA’s weather readings is controversial, but changing where D.C.’s official weather reports originate from would not be straight forward.
Weather measurements are taken at the airport for the primary purpose of supporting aviation - to advise the control tower of changing and potentially hazardous conditions.
“Our general job is reporting the winds, cloud ceiling and heights, and the visibility... that’s what we’re constantly watching... and we have to send that out to the control tower at least once an hour,” Richards said.
To establish an alternative station for D.C. where the monitoring of weather and climate is the primary motivation, resources would need to become available.
“I tried to establish a new station from within the NWS several years ago because of DCA’s unrepresentativeness for the area population but failed,” Leffler said in an email.
“I believe the only way a new official non-airport station will be opened in D.C. is for the private sector [print and broadcast] to coordinate a lobbying effort directly with NWS top management in Silver Spring, Md.”
But introducing a new observing location would disrupt the continuity of 70 years of DCA weather records.
“It’s been here since 1942... if we moved it now, I don’t know if the comparisons to other years would be accurate,” Richards said.
Where would you place D.C.’s weather station?
It might be an academic question, but fun to mull over: If there could be an alternative location chosen to record Washington, D.C.’s weather, where should it be (or should it remain at DCA)? Vote in our poll...