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Why is Cincinnati warmer than the suburbs?

Explaining why things happen in your forecast
Posted at 11:51 AM, Oct 18, 2017

Have you ever looked at the morning temperature map and wondered, "Why is Cincinnati so much warmer?"

This phenomenon is something meteorologist call the urban heat island effect. If you look at a regional map, you can see that several larger cities show up warmer at night. It's the bright green areas surrounded by blue in locations like Atlanta, Cincinnati and Birmingham.

Heat islands show up as a the bright green surrounded by blue

But how do cities remain relatively warmer at night?

Urban areas have more concrete, densely spaced buildings and less vegetation like trees and grass. That leads to warmer daytime because those materials heat quickly. Even at night, that heat isn't lost as quickly, leaving urban areas warmer too.

Rural areas tend to have less concrete, more trees and crops -- those elements don't hold onto heat as long. Trees actually have a cooling process called evapotranspiration, so the more trees, the cooler it can get.

Urban heat islands show up more drastically in the winter and summer, but the effect can also appear in the fall and spring when we have ample daytime sunshine and clear, cool nights. Our current weather pattern has been perfect to see this effect. 

When you hear the 9 First Warning Weather team talk about "the outlying areas being cooler than Cincinnati," this is the urban heat island effect in full display.

Follow Meteorologist Jennifer Ketchmark on Twitter, @KetchmarkWCPO, and tweet her your weather questions.