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Why there’s steam during or after rain

ALLISTER AALDERS weather@saltwire.com @allistercanada Allister Aalders is the weather specialist for the Saltwire Network, providing forecasts and analysis for Atlantic Canada. #Askallister

One of my colleagues, Sarah, and I were chatting while recently leaving work for the day. It was miserable outside as heavy rain arrived about an hour earlier, but oce we reached the parking lot, something caught our eye.

There was steam rising just above the pavement. This instantly prompted a discussion about why we were seeing this in the middle of heavy rainfall.

The key factor for this to happen is the temperature of the pavement, which was warmer than the surrounding air. This allowed some of the rain just above the ground to evaporate.

The next step can happen in one of two ways. The rain was bringing cooler air from the upper levels of the atmosphere to the surface, which could have allowed the evaporation to condense. The other option is that the air became filled with more water vapour than it could hold, forcing it to condense.

It’s not uncommon to see this happen during or after a rain event, mainly during the late spring and summer when the temperature of the pavement has the potential to be warmer than the surrounding air.

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2022-06-29T07:00:00.0000000Z

2022-06-29T07:00:00.0000000Z

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