Forecasting for contrails and how they form

This is what we use to forecast contrails in Australia, in the tropics where I am it is less likely for contrails to form, than it is in the mid latitudes

First off we need very cold and humid air. Temperature is a prime factor, in that if the temperature is warmer than approx -34 degrees celsis, then there is a zero percent chance of contrail development. Next factor is humidity. There is a zero percent chance of contrail development if the humidity is less than 40%. The chance increases as the air is moister because supersaturation is liklier to occur with more water and ice in the air

We determine air saturation and temperature by releasing radiosondes whihc are attached to weather balloons. The results are plotted on whats called an F160 or more commonly a skew T diagram.

Persistant contrails occurrence depends on the position of whats called the tropopause. The tropopause is the boundary that seperates, the stratosphere from the troposphere and is also the point at which the temperature stops decreasing an starts increasing again. In mid latitudes the tropopause is usually located in between 25,000ft and 35,000ft but is not always at a set height. The air below the tropopause can be frequently saturated with ice crystals while the air above it is frequently very dry.

Planes crusing below the tropopause will form persistant contrails when the air temperature is below -36 celsius (which is ALWAYS, no exception, check any skew T diagram to prove me wrong if you dare). Planes cruising above the tropopasue have a very unlikely chance of producing persistent contrails as the air is too dry for supersaturation to occur, thus contrails dont last for long.

When a plane passes through moist cold air, the hot water vapour in its exhaust freezes, the process usually takes less then a second. If there is ice crystals in the air (ie cold humid air), the water from the exhaust attaches itself to the ice effectively increasing it size and giving us on the ground a view of a white line. If a persistent contrail does from, there is a high likelyhood of cloud development in the coming hours. It is a good forecast tool to use for amatuer weather observers

Using data from the skew t diagrams, wind shear can be determined. This can spread the cirrus cloud into a layer, known to us as cirrostratus which spreads across the sky. Cirrostratus is often a precurser to rain as it suggests instability and a high presence of water vapour in the air

Now can someone please explain to me how/why chemicals allegedly sprayed by secret government organisation persist in the sky and spread out? Also try to explain....using your knowledge of meteorology, which you apparently all have....why water vapour will not do this.

And please use scientific answers...pictures and youtube videos are not acceptable

Hi Oz,
Thank you for the info. I do have a question for you.
Last weekend I was driving home, and in the distance in front of me I saw was looked like a chemtrail (Oops CONtrail ) but it was only (from my perception) about an inch long on approx 70 degree angle in the sky which to me seems a bit steep for an ascending plane. Now as it moved along, (upwards) the trail stayed the same length instead of leaving a long trail behind it. I thought it seemed weird at the time.

I know you will ask so here is some background....
It was dusk...around 5pm
It was in the 'general' direction of the airport
It was a warm day and no clouds
There was little or no wind
It was a fair but higher than most planes taking off
I had not been drinking

I am not making assumptions and don’t want to start people on any crazy ideas. I am just curious as to your thoughts on it.


[edit on 16/4/2008 by VIKINGANT]

reply to post by VIKINGANT


Well firstly the curvature of the earth probably gave you the impression that the plane was rising steeply when it wasnt really. I am not the best to ask about this one though

The trail was probably one caused by wing tip vortices. This occurs when the planes wings cause a sudden drop in air pressure which can cause water to condensate, but due to the aircrafts wake, the water is often disrupted and the trail will not last long.

The fact that there were no clouds suggests that the contrail wasnt formed from aircraft exhaust as the air may have (would have to check upper air obs to confirm) been too dry for a contrail to persist

So is there some sort of meteorological explanation of the black line phenomenon? I see it often, and it really makes me wonder. Im a skeptic to the fullest degree, but this sort of thing is baffling.

Just so you know, I dont believe in chemtrails, nor do I wish to, and I thought the black line thing was just the shadow or something explainable, but witnessing it for myself, it REALLY makes me wonder. Not to mention perturbed at myself for letting such a situation stump me.

(even if chemtrails are real, I dont believe in them)

reply to post by psychedeliack


Its called an edge trail which occurs when the contrail is in line with the sun. If you are in the proper position you will see the sliced edge of a shadow. This gives the impression that the trail is completely black.

There is also a parallel shadow which is the shadow of the trail cast onto an extremely thin almost transparent cloud beneath it. This also gives a black line. Many mistake this as something thats not normal but thast due to them not being able to see the thin cloud below

Originally posted by psychedeliack
So is there some sort of meteorological explanation of the black line phenomenon? I see it often, and it really makes me wonder. Im a skeptic to the fullest degree, but this sort of thing is baffling.

Just so you know, I dont believe in chemtrails, nor do I wish to, and I thought the black line thing was just the shadow or something explainable, but witnessing it for myself, it REALLY makes me wonder. Not to mention perturbed at myself for letting such a situation stump me.

(even if chemtrails are real, I dont believe in them)

Should have add this before

contrailscience.com...

This is a good link that explains the black line contrail phenomenen. Its all about sun position and the observers position in regards to the location of the contrail

those are not the same black lines. The black lines Im talking about do not parallel the trails at all, they precede the plane all together. When wind blows the trails, the black line stays perfectly aligned in front of the plane. If it were shadow, I would expect it to be the same as the object it is a shadow of. Not to mention the breaks in the contrail that did not match up with the black line.

As far as sun angles and viewer perspective go, I thought all that was common sense, but reading the chemtrail websites, people seem to just jump on the bandwagon without any analysis; thus the pictures associated with the black line phenomenon that have nothing to do with the black line phenomenon.

Next time I see it, Ill have to find a cam corder to record it to make sure to get video of the suns position and all that, unlike the still shots that dont help with sun location.

Anyways, I appreciate the help! You have a cool job!