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Tracking the heat? Why is the temperature reported at Austin's airport always a few degrees cooler?

The backs of people in a crosswalk dragging roller bags toward the airport entrance.
Julia Reihs
/
KUT
The temperature recorded at Austin-Bergstrom International Airport is always a few degrees cooler than the temperature recorded at Camp Mabry.

A lot of us are paying close attention to the temperature this summer as heat records fall like dominoes. But we are not all looking at the same thermometer.

There are multiple places around Austin where weather stations record data like temperature, wind speed and rainfall. There can be a surprising degree of variation between these stations. Simply put, where you get your weather information from can make a big difference in your understanding of the weather.

For example, as I am writing this sentence, Austin’s official weather station at Camp Mabry in West Austin has recorded 61 days of triple-digit heat this year. (Yikes.) The weather station at Austin-Bergstrom International Airport, another popular source for information, has recorded 46 triple-digit days. (Still yikes, but you see the difference.)

This is usually the way things are between the two weather stations. Measurements at the airport are typically a bit cooler than those at Mabry.

Why?

Heat islands and cooling culverts

For one thing, the urban heat island effect is not as strong at the airport.

The urban heat island effect is what happens when the built environment — the concrete, asphalt and metal of city structures — absorbs and traps heat. It makes things hotter in urban areas, and it makes it harder for the environment to cool down because all that absorbed heat continues to warm the air even after the sun sets.

The airport weather station is tucked away in a field on the southwest edge of the airport, near a runway, but far from the tarmac and parking lots that comprise some of the areas where heat sinks. There just aren't as many buildings around to absorb and trap heat.

“If you go out east there at Bergstrom, it's a little bit away from the city,” National Weather Service Meteorologist Andrew Quigley said. “So it's away from some of those urban effects that we speculate influence Camp Mabry."

But that’s not all.

It turns out the airport weather station is also positioned in what Quigley calls a “culvert,” or dip in the ground; cooler air sinks into it, yielding cooler temperature readings.

“The siting differences between those two stations can lead to those differences," he said, "first off, as we’ve seen this summer with heat, then also with low temperatures during the cool seasons."

The weather station of record

Those are two reasons why measurements at Camp Mabry are considered more representative of what’s happening in the city.

For researchers looking at long-term climate data, there may be a third reason to prefer Mabry information: It has a longer period of consistent record-keeping.

People have been recording the temperature at Camp Mabry since the late 1800s. Record-keeping started later at the airport.

Keith White, another NWS meteorologist, says it was initially done through manual observations back when the airport was the Bergstrom Air Force Base. But the National Weather Service changed the way it took the temperatures to an automated system several decades ago.

“It was, I believe, the late '90s when they stopped taking manual observations at the Air Force base,” he told KUT in 2021. “Then when it became the airport, we installed the system that takes our meteorological observations today.”

That weather station was installed in the culvert, leading to cooler readings than had previously been taken at the airport — a fact that could confuse researchers looking into long-term changes in temperature at that site.

So, if you hear conflicting information about how hot it’s been in Austin this year, find out where those numbers are coming from.

If you want the "official" records for the Austin area, find the Camp Mabry numbers. They're more representative of the weather in Austin, and the base is designated as Austin's official record-keeper by the National Weather Service.

Mose Buchele focuses on energy and environmental reporting at KUT. Got a tip? Email him at mbuchele@kut.org. Follow him on Twitter @mosebuchele.
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