The unusual industrial snowfall is thought to be due to the pollution recorded in the UK

A rare phenomenon known as industrial snowfall appears to have occurred near Heathrow airport earlier this year, according to a study.

Satellite imagery shows three large, white bands of land in parts of Surrey despite relatively dry conditions in the area at the time. The snow, recorded on 23 January, was distributed near industrial facilities south-east of Heathrow airport.

The only real explanation is that pollution caused the snowfall, said Dr Julian Mayes, an independent weather and climate consultant who saw the snow and wrote the study.

Anthropogenic or industrial snowfall can occur when moisture in the air condenses around small pollution particles, for example, forming snowflakes. The conditions must be right, with sufficiently low temperatures and plenty of atmospheric moisture. Only a few cases have been reported in the UK.

It started on what looked like a frosty morning, Mayes said, recalling how a freezing fog surrounded the village of West Molesey, Surrey, where he lives. It occurred to me that it was more than cold.

A snowy street in West Molesey on 23 January 2023. Photo: Julian Mayes

On closer inspection, he realized that the snow was very dry, like a dried coconut, and not as cold as it seemed to be deposited on the surface. It was confusing at first, Mayes said, because the area was under a ridge of high pressure and little rain was expected at the time.

A colleague alerted him to a satellite image of east Surrey, taken on the morning of January 23, which revealed three bands of what appeared to be light snowfall. Mayes hypothesized that a light wind pushed the industrial snow to the north-northwest, depositing it on the trails.

The satellite image also shows a small amount of passing cloud. However, it is unlikely that snow forms in clouds in a more general way, said Prof Giles Harrison, of the University of Reading’s meteorology department, who was not involved in the work. For frequent snowfall, a weather front would have to move through the area, and there is no evidence of this.

Mayes said other factors besides industrial pollution from land sources could influence the events of that day. This includes potential ice trails left behind by planes flying in and out of the airport. Moisture from nearby reservoirs can also have an effect.

But, he added, the evidence points to something that causes the water droplets in the fog to expand and freeze, forming snowflakes. The pollution is thought to provide footholds, or nucleation sites, that allow droplets to form into ice crystals.

This is particularly special, says Harrison, who co-authored a 2009 study of some of the UK’s snow industry’s earliest rainfall reports. Among them is an event related to emissions from a cider factory. A local person was quoted in the study as saying: There is a dusting of snow, and the snow has a hint of apple flavor.

Industrial snowfall is not usually predicted, so it can surprise observers, Harrison added.

The phenomenon was also reported in the US. A 2014 case in Amarillo, Texas, was blamed on steam from large power plants, which was believed to have turned to snow in the cold February air. People who work at the plants have noticed it for years, a spokesperson for local energy companies told the Amarillo Globe-News at the time.

This unusual form of snow is likely to become even rarer in the UK, says Harrison, as average temperatures are expected to continue to rise due to global warming.

Mayes added that his witnessing of the event was a perfect moment, as the snowfall was localized. If I lived a mile and a half away, I probably wouldn’t have noticed it, he said.

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