Finding: Jet aircraft trails create extra rain and snow from clouds

WASHINGTON—Planes flying over rain or snow can intensify the precipitation by as much as 10-fold, according to a new study.

The rain- and snow-bursts are not caused by emissions from the aircraft but are the peculiar consequence of the aircrafts’ wings passing though clouds of supercooled water droplets in cloud layers above a layer of active rain or snow.

Under the right conditions, this effect can boost rain and snow storms over airports, where many planes intersect the cloud layer on approach and descent.

“The interesting thing about this feature is that it is caused by aircraft, but it is not caused by pollution,” said Dimitri Moisseev, a researcher at the University of Helsinki and the Finnish Meteorological Institute and the lead author of the new study in AGU’s Journal of Geophysical Research: Atmospheres. “Even if there would be absolutely ecological airplanes, which don’t have any combustion, no fuel or anything, it would still happen.”

Although the bands of enhanced precipitation are artificially created, the physical process jump-started by the passage of planes can occur naturally, which makes them useful laboratories for studying the formation of precipitation, according to Moisseev. Observing them may help meteorologists “nowcast” natural rain and snow conditions 2 to 6 hours into the future, which is essential for airport operations.

“When you, like myself, look at the radar data every day there is always something interesting going on,” Moisseev said. “Surprisingly enough, there’s always new things that we cannot explain still.”

Moisseev discovered curious streamers of heightened precipitation in scans from the campus radar antenna at the University of Helsinki Kumpula. The unnaturally straight patches of intense precipitation appeared against a background of lighter rain or snow and seemed to bend toward the nearby Helsinki-Vantaa airport.

A radar station at Kerava, Finland, recorded a trail of heightened precipitation—the yellow streak to the left—on the aircraft approach path to Helsinki-Vantaa airport (EFHK) in March 2009.Credit: AGU/Journal of Geophysical Research: Atmospheres

Their shapes looked intriguingly like the inverse of cloud formations known as fallstreaks, hole-punch or canal clouds, phenomena which can occur when aircraft fly through clouds of water droplets that are colder than 0 degrees Celsius (32 degrees Fahrenheit) —but aren’t freezing.

The new study demonstrates that a similar phenomenon can enhance or elicit rain or snowfall from cloud layers underlying these supercooled cloud layers.


Air pressure changes from passing aircraft can trigger these supercooled water droplets to freeze into ice crystals. Air expands abruptly in the wake of wing and propeller tips, causing a dramatic local drop in pressure and temperature. Inside a cloud of water droplets that is already supercooled between -15 to -20 degrees Celsius (5 to -4 degrees Fahrenheit), the passing aircraft can drop the temperature below -40 degrees Celsius (-40 degrees Fahrenheit) and instigate the formation of ice crystals.Both tiny water droplets and ice crystals form clouds. Pure water can stay liquid down to -40 degrees Celsius (-40 degrees Fahrenheit) without dust particles or other suitable surfaces present to seed crystallization into ice. So water droplets that condense into clouds can be much colder than the typical freezing point of 0 degrees Celsius (32 degrees Fahrenheit). Such supercooled liquid clouds are common in low- to mid-level cloud layers.

The new ice crystals help freeze more supercool water droplets, setting off a chain reaction of crystal formation in a widening circle around the path of the aircraft. When the crystals fall, they create holes or streaks of clear air in the cloud, sometimes opening a window of blue sky if the cloud layer is thin. In most cases, the ice crystals evaporate before they reach the ground.

Meteorologists have known that passing aircraft can freeze water droplets into ice crystals and previous work had suggested that the process could enhance rain and snow in underlying clouds, but the effect had not been captured in detail.

Andrew Heymsfield, a senior scientist at the National Center for Atmospheric Research’s Mesoscale and Microscale Meteorology Laboratory in Boulder, Colorado, and a researcher unaffiliated with the new study, had noted the potential for inadvertent seeding of supercooled clouds over airports in a previous paper about the formation and spread of aircraft-induced holes in clouds. He observed similar arcs of heightened snowfall in radar data collected near Denver, Colorado’s former Stapleton Airport in 1992.

“Hole-punch” clouds like this one seen over Houston, Minnesota in November, 2014, occur when airplanes fly through a thin cloud of supercooled water vapor, causing water droplets to freeze. The tiny crystals fall, leaving a hole to mark the plane’s passage. When such supercooled clouds overlay a lower layer of precipitation, the falling crystals can instigate intensified rain or snowfall, according to a new study in AGU’s Journal of Geophysical Research: Atmospheres.
Credit: Jamie Vix.

“We know that planes can trigger precipitation. The authors of this study have a lot of cases, with wonderful data from ground-based instruments—radar, lidar—good information about particle size and concentration, and radiosonde data to show the likely temperature for formation,” Heymsfield said. “They succeeded in documenting the phenomenon.”

To find out if the streamers of heightened precipitation could be caused by aircraft, Moisseev and his colleagues reviewed 11 years of the University of Helsinki’s weather radar data and found 17 days with repeat cases of the characteristic linear streamers between December 2008 and January 2018.

They examined flightpaths near the airport to see whether the streamers could be caused by passing aircraft. Flightpaths archived to 2011 confirmed aircraft passed within 2-10 kilometers (1-6 miles) of the intense precipitation streamers in most of the cases observed.

“The intensified precipitation basically follows the track of an airplane above the cloud,” Moisseev said. “It could extend over hundreds of kilometers, but the cross-section would be maybe 100 meters. So it’s a very narrow, long feature.”


The additional ice crystals raise the rate at which crystals collide to form larger snowflakes, intensifying snowfall, according to the authors.

This could happen if an airplane flies directly through a precipitating cloud, but the authors suspect something more complicated is going on, because their data locates the starting height of rain and snow enhancement far above the layer that is already precipitating.

The new study concludes the airplane-generated ice crystals most likely fall from a supercooled upper cloud layer into a lower layer that is actively raining or snowing, begetting more rain or snow from the lower cloud layer.

Satellite data support this scenario, showing a top layer of clouds composed of supercool droplets or a mix of ice and water, poised at about the right temperature to turn to ice crystals under the influence of aircraft. This upper, supercool layer floats at the typical approach altitude of planes flying into the Helsinki-Vantaa airport.

Rain and snow artificially enhanced by air traffic has useful clues for natural precipitation and the factors affecting the efficiency of formation, according to Moisseev. The streamers are accidental experiments that allow the researchers to observe the effect along the path of the aircraft, and just outside it, and ask questions the kinds of microphysical processes taking place.


This paper is freely available for 30 days. You can download a PDF copy of the article by clicking on this link:


EDITORIAL NOTE: Any discussion of “chemtrails” in comments will be deleted. This is why. – Anthony

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February 12, 2019 12:15 pm

Ban all flights in the mid-west USA in the winter months, win-win /sarc

Bryan A
Reply to  vukcevic
February 12, 2019 12:33 pm

Have more flights over mountainous terrain and over Watersheds during rain events at times of drought to increase precipitation amounts

Reply to  vukcevic
February 12, 2019 2:14 pm

It must be true, Wimbledon tennis courts are under Heathrow airport flight path, and as everyone knows it always rain during the Wimbledon June/July tennis tournament./sarc

Bill Powers
Reply to  vukcevic
February 13, 2019 9:49 am

I wonder if three airports in and around DC explains all that hot air emanating for Capitol Hill?

R Shearer
Reply to  vukcevic
February 12, 2019 4:08 pm

Another clear advantage of trains. The faster we switch the better.

Bryan A
Reply to  R Shearer
February 12, 2019 7:39 pm

Still waiting for that intercontinental train

Bill Powers
Reply to  Bryan A
February 13, 2019 9:47 am

We can start with AOCs bridge to Hawaii. They can connect it off the California Merced to Bakersfield line.

Reply to  Bill Powers
February 14, 2019 11:30 am

We can have AOC stand on the California shore line and toss rocks into the ocean to form the bed for the rails.

Reply to  R Shearer
February 12, 2019 9:31 pm

How is not producing s small, very localised increase in precipitation a “clear advantage of trains”

I suppose you are implying the other clear advantage is “carbon”.

Well, if we had less planes there would be less ionization nuclei in the stratosphere and you would be waling about even more global warming.

February 12, 2019 12:22 pm

Observing them may help meteorologists “nowcast” natural rain and snow conditions 2 to 6 hours into the future

Well apart from the excuse to use a stupid, made up word, how does this differ from FORECASTING 2 to 6 hours into the future. That is what forecast means.

Reply to  Greg
February 12, 2019 12:27 pm

A “nowcast” is called a weather report, not a 6h prevision.

February 12, 2019 12:24 pm

The way aircraft punch holes in solid cloud cover has been well documented for years. This is not a “discovery”.

Reply to  Greg
February 12, 2019 2:19 pm

They didn’t say it was.
The mechanism behind why it punches holes was the discovery.

Reply to  MarkW
February 12, 2019 9:51 pm

The claimed mechanism is pure speculation ( hypothesis ) , not a “discovery”. Since they are using low resolution radar and attributing effects on the scale of 10km, they have no way of determining whether it is engine pollution or wing depression.

I see nothing in the paper even attempting to differentiate between the two.

February 12, 2019 12:42 pm

Flightpaths archived to 2011 confirmed aircraft passed within 2-10 kilometers (1-6 miles) of the intense precipitation streamers in most of the cases observed.

Sound like pretty handwavey “correlation”. I see no account of why this is supposed to be caused by a momentary pressure drop rather than nucleation by exhaust pollutants. If they are ready to stretch causation to 6 miles, they are not able to differentiate between wing depression and exhaust trails.

There are contrails from wing tips during cold conditions but these are dwarfed by the engine contrails. This all sounds like speculative nonsense to me.

Reply to  Greg
February 12, 2019 2:23 pm

…caused by a momentary pressure drop rather than nucleation by exhaust pollutants.

Nucleation requires particulate carbon, which there isn’t a lot of coming out of a modern jet engine. Most of the jet core exhaust is pure gas. Engineers have been working on the combustion process in these engines for decades to improve efficiency and any unburnt fuel means inefficiency. And in fact, the real job for a high bypass engine is to move air and it does that very well.

If you ever have piloted an aircraft (I have), you will understand supercooled water. If you don’t you might find yourself fighting a losing cause against aircraft icing flying through clouds that are still wet but below freezing. Just the pressure difference of the air passing over your aircraft and wings can cause the droplets to freeze immediately on the airframe and this can kill you. In certain instances just one minute in this environment can ice your airplane enough to put you on (in) the ground.

Now drag a B777 or A350 through a cloud deck at 300 knots and the air movement around it and its wings generate vortexes that are truly impressive. These vortexes can last for quite a long time. There is a reason air traffic control makes you stay at least 5 miles behind a “heavy”, and if you are smart you stay above their flight path as the wake vortexes tend to descend over distance.

An aircraft flying through an airmass doesn’t create a momentary pressure drop. It creates a violent movement of air and the bigger the airplane and the faster it goes, the more chaos it creates. The gist of this article makes perfect sense, not speculative nonsense.

R Shearer
Reply to  rbabcock
February 12, 2019 4:10 pm

Ammonium sulfate aerosols make great nucleation sites.

Reply to  R Shearer
February 12, 2019 10:01 pm

Indeed. Despite the current obsession with “carbon” , that is not the main source of condensation nuclei from a jet engine.

Thanks to rbabcock for some real flying related information about ice. That is well known. I did not say wing depression did not exist , I said there study shows no way of differentiating between the two.

If you look at contrails from descending aircraft there are contrails from wing tip vortices but these are minor in comparison to the engine contrails. They would need some pretty strong evidence to suggest that the effect they measure is due to depression , not engine induced precipitation and they offer NONE. That is why I said it was speculative nonsense.

Sadly this now seems to the norm in published papers.

Reply to  rbabcock
February 12, 2019 11:20 pm

Here is a nice demonstration of the turbulence rbabcock refers too.

Here is one visualising wing depression induced condensation at ground level.

Obviously no ground level contrails, that only happens in Siberia at -40 deg, or outside the Pentagon in early September.

Loren Wilson
Reply to  Greg
February 12, 2019 2:50 pm

I propose a test using a glider – same wings but no combustion. It may not go fast enough to cause the pressure drop and temperature drop to initiate ice crystal formation. We need an aeronautical engineer to provide a table of air pressure over a wing as a function of velocity. The adiabatic temperature change can then be calculated.

Crispin in Waterloo
Reply to  Loren Wilson
February 12, 2019 6:10 pm

Throttle back a 747 and let it glide through a cloud layer same test, big turbulence.

Reply to  Crispin in Waterloo
February 12, 2019 9:30 pm

747’s glide?!?

Craig from Oz
Reply to  SMC
February 12, 2019 10:06 pm


Gliding gives the flight crew something to do while waiting for all four engines to restart after passing through volcano ash. (BA Flight 009, 1982 and KLM Flight 867, 1989).

Probably not something you want to do for fun, but definitely possible.

Reply to  SMC
February 13, 2019 2:06 am

Modern jets usually have a best glide ratio of 1:15 to 1:20.

Reply to  SMC
February 13, 2019 5:08 am

Flight 800 did, the CIA says so it has to be true.

Loren Wilson
Reply to  Crispin in Waterloo
February 13, 2019 4:03 pm

Even better than my test – how do we talk the ATSB into letting us do this?

Reply to  Greg
February 17, 2019 4:29 pm

I see no account of why this is supposed to be caused by a momentary pressure drop rather than nucleation by exhaust pollutants. If they are ready to stretch causation to 6 miles, they are not able to differentiate between wing depression and exhaust trails.

The authors quote “Woodley et al. (1991) have shown that aircraft exhaust is of negligible importance in aircraft-produced ice particle formation”, which made that case quite nicely. Exhaust pollutants are excluded by stipulation via Woodley, and Woodley et al were pretty thorough in their investigations.

The authors showed how the ice particles from the aircraft wake were measurably different than the surrounding precipitation, matched with individual aircraft, and could take between 20 and 40 minutes to fully develop into precipitation. During that time the LIP tracked with the advection movement of the weather system from where the aircraft had been. So, the up to 6 mile displacement in space is really just a displacement in time.

Finally, engine contrails are not the result of pollutant caused nucleation, but instead are caused by direct injection of excess moisture into the atmosphere as a byproduct of combustion.

February 12, 2019 12:44 pm

Very interesting article. Thanks Anthony.

February 12, 2019 1:12 pm

I think this might be happening with wind turbines as well. More so with helicopters.

Reply to  Martin557
February 12, 2019 10:15 pm

Good point. Downwind cloud formation is well known in wind farms. At least that avoids the problem of confounding the effects of engine pollution and wing depression.

Reply to  Martin557
February 12, 2019 11:46 pm

Helicopter depression “contrails” , Arctic.

Reply to  greg
February 13, 2019 5:14 am

That was pretty cool. I have seen choppers do a lot of interesting things in high humidity conditions, first time I saw vap trails that clear and long.

February 12, 2019 1:47 pm

So … this is just like the contrails spewed by the US military to brainwash the population into believing Muslims flew planes into the WTC and Pentagon? Yeah … I read that on a “Truther” dark website somewhere. Came out of Macedonia, if I remember HER correctly …

February 12, 2019 1:54 pm

“….by as much as 10 fold…” extraordinary claims require extraordinary evidence….people who live under flight paths should have much more snow than average….which they don’t….

Reply to  DMacKenzie
February 12, 2019 10:08 pm

They do produce observational evidence of a significant increase, however it is a very localised effect in both time and space and not likely show up on daily totals or measured thickness of ground snow cover.

February 12, 2019 2:12 pm

Those researchers left out the part about the hot air emitted by politicians and newscasters. That should certainly have a noticeable effect on this phenomenon. They disturb everything, including the weather.

Reply to  Sara
February 12, 2019 4:14 pm


February 12, 2019 2:26 pm

I know several educated, productive who believe in the ChemTrail conspiracy.

Reply to  brians356
February 12, 2019 4:16 pm

I know several “educated, productive . . . ” who believe in the CAGW conspiracy.

Reply to  sycomputing
February 12, 2019 10:35 pm

“Educated”in what? Science requires formal proof based on observation, not a consensus of “belief”.

Reply to  Greg
February 13, 2019 11:14 am

*sigh . . . *

John Endicott
Reply to  brians356
February 13, 2019 7:33 am

I was wondering how long it would take for a post referencing ChemTrails to appear. Didn’t take long.

Reply to  John Endicott
February 14, 2019 5:04 am

Yea, lots of idiots believe stupid things.

February 12, 2019 2:53 pm

Would have fallen anyway….

Jimmy Haigh
February 12, 2019 3:34 pm

Planes generally fly very low over airports….

Nick Werner
February 12, 2019 4:22 pm

“Planes flying over rain or snow can intensify the precipitation by as much as 10-fold, according to a new study.”

Coming soon, another climate science study: “After adjustments for the increasing number of airplanes flying over California, we found that there has been no pause to its never-ending drought.”

February 12, 2019 5:03 pm

The ‘hole punch’ picture was great.

I’ve been reading here since 2008 +/- and if I saw an image of a hole punch, I don’t recall it.

That was a treat! Thanks.

February 12, 2019 5:57 pm

Very interesting post/article.

February 12, 2019 6:01 pm

Particulate matter in the atmosphere contributing to rain/snow? What a unique idea!

February 12, 2019 6:37 pm

Decades ago I was involved in evaluating a MoS2 showing on the BC coast just in from Juneau,
Lot of helicopter work in quickly changing atmospherics.
Such as the rotors creating enough fog to mess up your vision.
The pilot would get away from there fast.
Er, the “Moly” is still there–a big classic system but under an Alpine glacier.

Reply to  Bob Hoye
February 12, 2019 10:12 pm

Interesting. Are you saying that the chopper are releasing measurable amounts of MoS2 ? Is that engine or rotor lube? What is that about?

Flight Level
February 12, 2019 7:13 pm

“of the aircrafts’ wings passing though clouds of supercooled water droplets in cloud layers above a layer of active rain or snow”

Also known as “icing conditions”. The monster that has taken too many down. Needless to say that we, those who can tell about, avoid it unless stringent fuel savings (save the earth…) prohibit a route change. Then we’ll weight our options to divert or go back, recall the extend our life insurance coverage and decide how to punch thru. No matter anti-icing and on-board voodoo incantations generators.

Such skies come often with a free bonus of truly deranged up/down drafts a gogo which all combined may knock-off autopilots. Next level of fun, stall recovery and memory numbers for pitch&power before we get out of there. Not the right moment to disrupt the flow and flame out these very sensitive high bypass eco-friendly vacuum cleaners.

What gives ? Only a small minority of poor souls will risk there while the majority takes a joy-ride to avoid that space. There’s nothing to generalize on the putative aircraft impact on this type of often very localized weather system.

Sure we command weather, torrential rains or desert burning sun. It all depends on what we load in our secret chemtrail tanks and program the voodoo generators. But hey, that’s a state secret.

February 12, 2019 8:10 pm

Bursting the clouds for better communication
October 18, 2018, University of Geneva

“We want to get around the problem by making a hole directly through the clouds so that the laser beam can pass through,” explains Professor Wolf. His team has developed a laser that heats the air over 1,500 degrees Celsius and produces a shock wave to expel the suspended water droplets sideways. This creates a hole a few centimetres wide over the entire thickness of the cloud. The discovery of these ultra-powerful lasers has just been awarded the 2018 Nobel Prize for Physics. “All you then need to do is keep the laser beam on the cloud and send the laser that contains the information at the same time,” says Guillaume Schimmel, a researcher in the team led by Wolf. “It then slips into the hole through the cloud and allows the data to be transferred.”

Read more at:

Dennis Sandberg
February 12, 2019 8:30 pm

“…can intensify the precipitation by as much as 10-fold, according to a new study”. Can? Maybe? Might? Think about it. Let’s say an inch of rain would fall in an hour if no planes pass through, but now we get 10″ in an hour? Not likely. Maybe if 0.10 inch would have fallen we instead would get an inch? Doubtful. Maybe if 0.01 would have fallen without the airplanes we get 0.10 inch, likely but so what? Qualitative comment without quantitative observation is just worthless blabber.

Craig from Oz
Reply to  Dennis Sandberg
February 12, 2019 10:11 pm

You seem to be assuming there is a linear relationship. Without reading the paper myself I am going to assume that the authors have not made this claim and are possibly referring to rain increases at the lower level of rainfall.

A 0.1mm fine drizzle that increase to 1mm under the flight path is still a 10-fold increase after all.

Open to correction but I believe the claim is still valid.

Dennis Sandberg
Reply to  Craig from Oz
February 12, 2019 10:31 pm

Craig, we’re saying the same thing. All I added is instead of a very, very fine mist, the planes cause a very fine mist so who cares? It’s a nothing burger. Reminds me of alarmist’s complaining about CO2 going from 300 ppm to 400 ppm….much about nothing….except as “modeled” in a few thousand taxpayer paid for “papers”.

John Robertson
February 12, 2019 9:17 pm

No more drought then?

February 13, 2019 12:04 am

The rain- and snow-bursts are not caused by emissions from the aircraft but …

I don’t see anywhere where they present evidence to show that.

Johann Wundersamer
February 13, 2019 3:17 am

“The interesting thing about this feature is that it is caused by aircraft, but it is not caused by pollution,” said Dimitri Moisseev, a researcher at the University of Helsinki”

The effect is simply that the cold air is heated as it passes through the turbine.

The expelled air becomes visible by water vapor.

when the sky is clear and there is little air movement / winds, the trails remain visible for a long time but thin out, join together to visible clouds.

in the otherwise clear sky.

Thomas Edwardson
Reply to  Johann Wundersamer
February 17, 2019 5:31 am

Contrails are not formed by heating the air as it passes through the engine. Contrails are formed by direct injection of water vapor into the atmosphere. Burning aviation fuels goes something like this …
2 C12H26 +37 O2 –> 24 CO2 + 26 H2O
That last term on the right is the water vapor that becomes visible whenever the relative humidity is close enough to the saturation point that the water vapor added as a byproduct of combustion pushes the local humidity over 100%. The length of time the contrail remains visible is a direct indication of relative humidity at flight level. When the air is quite dry, the contrail is short, and disappears quickly as the jet wash mixes with the local atmosphere. When the air is more humid at flight level, the contrails can persist for hours.

February 13, 2019 8:58 am

Say what?
Tell me it isn’t so, that SCIENTIST is now promoting a variant of “chemtrail” conspiracy theories.

February 13, 2019 10:24 am

There was a study done by National Center for Atmospheric Research released in 2010 that was similar.
Aircraft cause precipitation, hole-punch clouds.

Peter D.
February 14, 2019 12:37 pm

Stop blaming the planes for the rain. AGW is making the clouds bigger. I’ve seen them; they are fluffier and fuller(from water vapor). In the 70’s clouds were much smaller than they are today.
Stop denying that GW is making the clouds bigger and fuller. The rains from these bigger clouds are making the rain, rainier.

[citatations, studies, measurements? Any proof at all besides your opinion? -mod]

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