Rooftop Temperatures And How They Compare With Standard Surface Observations

The location and immediate exposure of weather instruments is extremely important for the collection of consistent and representative weather data. Adherence to standards in weather station instrument exposure is essential in order for data to be comparable from one location to another and over time at a single location. However, for reasons of convenience, cost and security, weather stations have sometimes been installed with non-standard exposures such as on the roofs of buildings. Recently, the National Weather Service has made a concerted effort to replace roof-mounted weather stations with regular surface stations. But at the same time, there has been a rapid expansion of non-federal weather stations, some of which are roof mounted. The concurrent expansion of electronic communications has allowed these observations to be immediately available to a wide audience including the public, private companies, students and teachers, media, the National Weather Service and other government organizations. In the short term, potential data problems associated with rooftop exposures have been overlooked in favor of the benefit of immediate access to more data.

Rooftop temperatures are often warmer than standard surface temperatures, but no simple bias or correction applies in all situations. Recent observations have shown that there is considerable variability between rooftop observations and nearby ground-based weather stations. In fact, localized temperature variations can be significant even on a single roof, depending on surface materials and the proximity to side walls. In this presentation, physical causes for differences between rooftop and surface observations will be discussed based on observations of surface radiating temperatures in combination with ground and rooftop thermometer readings. A local microscale network of temperature sensors is now being utilized to better define these local variations.