City weather cooles, to a degree Station: The National Weather Service's move from a hot roof to a grassy knoll has cooled readings, if not temperatures.


It was plenty hot this week in downtown Baltimore. It's only the thermometer that has cooled off.

At the end of April, the National Weather Service moved its

downtown weather station from the broiling rooftop of the old Custom House on Gay Street, to a grassy patch across the Inner Harbor.

Since then, the official daily highs reported for downtown have been lower, by as much as 9 degrees, than those that would have been reported from the Custom House. The overnight lows have been as much as 12 degrees cooler.

On paper only, it's been an average of 4.4 degrees cooler during the day, and 2.3 degrees cooler at night in downtown Baltimore since the new weather station was switched on.

For example, Tuesday's downtown high was 100 degrees at the Custom House. But weather broadcasters, using the new Science Center data, told the sweltering city the high was only 97.

On Wednesday, Baltimoreans heard the downtown temperatures had reached 96 degrees. But how much more justified their complaints would have sounded had they been told it was 102 degrees on the roof of the Custom House. No matter that nobody lives up there.

The changeover has halved the number of days with highs of 90 degrees plus - just 18 since May 1 instead of the 36 days clocked at the Custom House.

And, while the old weather station has recorded four days this summer with highs of 100 degrees or more, officially - at the Science Center - there have been none.

It's a truth-in-science thing.

Meteorologists have known for years that the thermometer atop the Custom House was unreliable. It stands in an artificial "heat island" - heat absorbed, reflected or generated by the Custom House, its rooftop utilities and by other buildings around it.

People down on the street simply weren't as hot as they were being told.

Urban "heat island" readings are one reason Baltimore's station-of-record since 1950 has been - and remains - at Baltimore-Washington International Airport in Anne Arundel County, six miles from the Inner Harbor.

Downtown readings are useful to urban residents, however, if they're accurate. So in the spring the weather service spent $50,000 on a new, automated weather station, and erected it on the lawn just east of the Science Center.

It records not only temperature, but also precipitation, humidity and barometric pressure. The data are transmitted automatically telephone line to the Baltimore-Washington forecast office in Sterling, Va.

For research purposes, the weather service will continue to record data at the Custom House for a year before dismantling the old station, said meteorologist Tom Doughtery, of the Sterling office.

Custom House data are posted on the Internet (at - at least for now; a forecaster yesterday suggested they shouldn't be made public because they are no longer official readings. In any case, they are branded with a warning in red capital letters: "NO GUARANTEES ABOUT ACCURACY."

Pub Date: 7/25/98

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