ST. GEORGE — People have noticed it more lately, especially in the first part of the morning. Condensation trails, or contrails, across the sky.
Local posts on social media have been filled with theories ranging from wondering why so many planes are flying over St. George to theories that the contrails are a plot to influence the election.
But according to meteorologists from the National Weather Service, it’s actually something simpler: it’s getting colder.
The chemical recipe those contrails jet planes make in the sky is two hydrogen molecules combined with one oxygen molecule – otherwise known as water.
“Contrail formation is a function of the humidity profile,” Darren Van Cleave, the meteorologist in charge of the National Weather Service’s Salt Lake City Office, told St. George News. “When there is sufficient humidity at the levels jets are flying, the exhaust starts a process that creates ice crystals.”
The exhaust of jet engines produces water vapor as a by-product. In the same way that breath can be seen when it’s colder, that water vapor becomes an icy cloud – especially as it’s always colder in the upper atmosphere even on the hottest summer’s day.
Those chillier mornings the last week or so have had an even chillier effect in the upper atmosphere, Van Cleave said.
“Lately, we have had persistent clear skies over Southern Utah with enough humidity at higher levels of the atmosphere for contrails despite dry conditions at the surface,” Van Cleave told St. George News.
As the weather service explains on this page, the air can only carry a certain amount of water, and cold air can hold less water than warmer air. That’s why drops form on an icy glass of lemonade on a summer’s day, a person can see their breath on a cold fall or winter morning and why the water vapor exhaust from jet engines forms cloudy streaks when it’s colder and more humid in the upper atmosphere.
Still, there are those, mainly on social media, who say the exhaust from jet planes is actually the dispersing of chemicals on the populace below. One post on a local Facebook group this week urged the St. George City Council to investigate “why they are spraying the skies of St. George every day.”
While there have been no peer-reviewed studies that support the chemtrail theory, there are a multitude of studies on the water vapor produced from the exhaust of jet engines and none have reached the conclusion it is anything more than the condensation of water.
In a web post, Harvard physics professor David Keith looked into the chemtrail theory and said there is no evidence to suggest it.
“If you think that aircraft contrails ‘look different’ or are ‘behaving strangely,’ consider that regular aircraft condensation trails are sometimes long-lasting and the way they look can change suddenly along a flight path as aircraft fly through regions with different temperature and humidity,” Keith said. “This is well understood and has been demonstrated by ground observation and by scientific research performed by thousands of people over many decades. Extraordinary claims require extraordinary proof.”
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