EXPERIMENT: Can I forecast "chemtrails"?

Over the past few mornings I have been observing the appearance or non-appearance of persistent contrails (commonly described, incorrectly, as "chemtrails") above my house, and relating it to the atmospheric conditions using Skew-T plots from nearby balloon soundings.

There's a nice correlation, so the obvious next step is to see if I can forecast in advance whether or not these so-called chemtrails will appear, using predicted soundings from weather models.

Now, I want to make it clear that I am not expecting to be able to get 100% accuracy, for reasons I'll go into later, but it should be an interesting exercise.

In some ways I wish I'd started this thread yesterday, as the prediction was a very easy one to make. Tomorrow's looks less clear-cut at the moment. Allow me to explain by taking yesterday and today as examples...

Wednesday July 2
Plenty of spreading contrails, which eventually formed fairly solid cirrus sheets.


Thursday July 3
No trails visible. Some scattered high cloud at first, which cleared not long after this photo to leave very clear blue skies (NB the faint vertical lines visible at top right are simply the reflection of the curtains!)


Now, here's the science bit.



This chart is taken from a 1981 paper on forecasting contrails, produced by the Air Weather Service (now Air Force Weather Agency) at Scott AFB.

It might look complex, but basically it shows the relative humidity required for contrail formation at different temperatures and pressures. The percentages are NOT probablities: they show the RH needed at that given temperature and pressure. Because the RH can never be higher than 100%, you should not see contrail formation if the conditions are to the RIGHT of this line, and because the RH can never be lower than 0%, you should always see contrail formation if the conditions are to the LEFT of this line. (Don't take "always" and "never" too literally, though: it is only a guideline worked out by observations in the past.)

Now we can look at the forecast soundings for the days in question. This was the previous day's forecast for 6am GMT (7am BST) on July 2:



The forecast unfortunately only goes up to 300mb, which is about 30,000ft, but you can see that the forecast there showed the air temperature (red line) to be about -44ºC, and the dewpoint (blue line) to be only very slightly lower, at about -45ºC. This implies a RH very near to saturation point, >90%. From the contrail chart, contrail formation would only require maybe 80% RH, so contrails should form.

Now the forecast for this morning, July 3:



The air temperature at 300mb is forecast to be rather warmer, -38ºC, with a dewpoint of about -44ºC. Referring back to our chart, contrails should need an air temperature colder than -42ºC to form even with 100% humidity, so contrails should not form.


Now, as I said, I am not claiming this is going to be an exact science. Here is what could go wrong:

1) The model soundings only go up to 300mb. A lot of planes fly higher than this. 250mb is more accurate for most cruising airliners. So, if the air supports contrails at that height, I'm not necessarily going to see it, although if the conditions are very suitable or unsuitable at 300mb then I am assuming they will not be too different at 250mb.

2) It's only a model. If the model data is not accurate, it won't match the real world. Also the resolution of modelled data is far lower than actual, real world soundings.

3) The chart was drawn 33 years ago. Modern engines tend to create contrails under conditions that older ones might not have done, although this effect should be fairly small.

With all this in mind, I intend to make some predictions on this thread and test them out. Accusations that I am being briefed by the Black Hats who plan the spraying days gratefully accepted...

a reply to: Rob48

Good luck with this. I hope some of the chemtrail crowd will follow your experiment.

Maybe a link to the source for the plots?

a reply to: Rob48

Good idea.

Not sure the "mystery spray" crowd will acknowledge it though. They don't listen to reason anyway. And some of them promote the BS anyway to distract the conversation away from air pollution on runways or at altitude.

Its only too simple to look up at the sound of hi flying jets and see that on some days atmospheric conditions are right for condensation and on others, not.

Like on some days you see your breath and some days… not.

originally posted by: mrthumpy
Maybe a link to the source for the plots?

Sure, they are at WeatherOnline.

The model data used comes from the GFS (Global Forecast System) model which is run by the US National Weather Service. It covers the whole globe (hence the name!) and has the most freely available data of any available model. (The advanced data from, say, the UK Met Office models is only available to paying cutsomers.)

I am using the London Heathrow location, which is less than 20 miles from my home.

Edit: I've also just found another source for GFS maps which shows the 300mb relative humidity directly, rather than having to calculate it: Link.

A neat comparison between the July 2 and July 3 conditions at 30,000ft here!



In fact the same site also shows temperature maps at 300mb, which may be an easier-to-use resource for my forecasts.

a reply to: Rob48

Rob, I am not as good with meteorology as you seem to be, but we currently have a hurricane passing by our coast. In my experience, just after a storm like that passes, there is at least a day and a half of real nice weather. Kind of a gift for putting up with bad weather. It's also forecasted to be nice weather after this passes.

Could you post a prediction on this and I will take some pictures during the day to help prove your point.
If you are too busy, don't worry about it. I just plan to be around the grill and cooler and can multitask and take pictures while maintaining my beverage supply.

Again, good luck.

Dunn, NC, but eastern NC Sampson/ Harnett/Johnston counties are all within a few miles.

a reply to: network dude

Hi, I'll give that a go a bit later. When would you like the forecast for - tomorrow?

In the meantime, on to the first forecast for my area.

I'm using 6am GMT (7am British Summer Time), as that is around the time I wake up and I can easily check for morning contrails.

The charts for tomorrow, July 4, at that time based on the latest GFS model run (12 noon today)...



300mb temperature is almost exactly -40ºC.



300mb RH looks to be about 60%, albeit that is quite a narrow dry slot.

So, at the 300mb level it looks a fairly easy call for no chemtrails.

HOWEVER... I have now managed to find plots with the 250mb data: Link.

Now it gets a bit tricky.



250mb temperature = -48ºC. Dewpoint = -55ºC. Using the online Humidity Calculator this gives a RH of 71.5%. Or, if you use the WMO measure of RH, which takes into account supersaturation potential, this drops to only 44.6%. At the moment this is where my level of expertise runs out and I'm not sure which is the most appropriate measure to use. This will be a learning process!

Going back to the contrail chart, it appears that a 250mb temperature of -48ºC requires a humidity of about 80% for contrail formation.

So, my somewhat more tentative forecast for tomorrow morning is still:

NO CHEMTRAILS!

originally posted by: Rob48




although if the conditions are very suitable or unsuitable at 300mb then I am assuming they will not be too different at 250mb.

2) It's only a model. If the model data is not accurate, it won't match the real world. Also the resolution of modelled data is far lower than actual, real world soundings.

3) The chart was drawn 33 years ago. Modern engines tend to create contrails under conditions that older ones might not have done, although this effect should be fairly small.

With all this in mind, I intend to make some predictions on this thread and test them out. Accusations that I am being briefed by the Black Hats who plan the spraying days gratefully accepted...

I'm glad to see someone approaching this topic with a little science. But your assumption about the homogeneity of the atmosphere in the 250 to 300 mb regions needs some work. At these altitudes, you are getting pretty close to the tropopause, which is the point at which the temperature lapse rate ends. At about the 200 mb level the temp starts rising a little. And there is atmospheric mixing. You can get some noticeable temperature changes even at the same altitude. We routinely cruise at the 41,000 to 51,000 foot level (pressure altitude.) And if you set the autopilot on an altitude hold setting of, say, 45,000 feet, you can get some speed fluctuations that can bring you close to the never exceed mach speed limit. Because mach number is directly dependent on temperature, your 250 ton metal tube can increase mach number quite a bit with a few degrees temperature change. And busting Mmo, which is the mach number version of a never exceed speed, can have, and in the past, has had, some dire consequences. The center of gravity of an airplane is in front of the center of lift. The horizontal tail balances the whole thing. Think of a seesaw with 2 people - a fat guy sitting very close to the center with his skinny friend sitting at the other end. As you increase speed in the airplane, the center of lift moves rearward. It's like the fat guy moving farther out on his half of the seesaw. At some point, his moment arm exceeds the moment arm of the skinny guy and WHAM!, fat guy crashes to the ground and skinny guy gets launched into space. In an airplane that's called "mach tuck" and the aircraft upsets into a probably unrecoverable dive, shedding wings and tai land becoming a huge lawn dart. To combat this fluctuation of temperatures, we can use a different mode on the altimeter. We can use a mach number hold setting instead of altitude hold. You need an ATC clearance to do this since your altitude is going to go up and down while the autopilot wears its little electronic brain out holding exactly .88 Mach, or whatever. In any event, the real world at 50,000 feet is not what you might expect.
Also, you can get situations at high altitude where therelative humidity, particularly RHi (ice) is over 100%. The air that high is very clean and until a jet goes through spewing stuff, it lacks enough condensation nuclii to cause condensation or deposition. This is called supersaturation and it contributes greatly to contrail formation.

Great thread, there is another on ATS that followed weather data for a while as well. The funny thing is, no matter what scientific methods you come up with, the "chem"trail believers are always overcome by confirmation-bias.

I don't know if it would help, but NASA/Langley has this contrail forecasting tool here:

Contrail Formation Forecast Tool

originally posted by: network dude
a reply to: Rob48

Rob, I am not as good with meteorology as you seem to be, but we currently have a hurricane passing by our coast. In my experience, just after a storm like that passes, there is at least a day and a half of real nice weather. Kind of a gift for putting up with bad weather. It's also forecasted to be nice weather after this passes.

Could you post a prediction on this and I will take some pictures during the day to help prove your point.
If you are too busy, don't worry about it. I just plan to be around the grill and cooler and can multitask and take pictures while maintaining my beverage supply.

Again, good luck.

Dunn, NC, but eastern NC Sampson/ Harnett/Johnston counties are all within a few miles.

OK, I've just had a skim through the charts. Looks to me like the next good opportunity for some chemtrail spotting in your area could be in about 48 hours' time. The upper air looks too warm tomorrow (and it's going to be mostly overcast), but on July 5 it cools down to just below -45ºC, which should be just cold enough, and there is a wedge of very humid air moving in to NC:



That chart is for 2pm on Saturday, Eastern Daylight Time if my sums are right!

So, have a look around the middle of the day on Saturday, although there might still be a bit of cloud hanging around...

a reply to: F4guy

Thanks for your input. Since I wrote that bit I have managed to find model data going above 300mb which means I have to rely less on assumptions.

Regarding supersaturation, I did touch on that with my calculations above. For instance with a dewpoint of -45ºC and a temperature of -44ºC the unadjusted RH comes out at 138.5%, which indicates supersaturation. Those were the figures for July 2 which was indeed a very good day for contrails! I guess the lesson here is to use the raw RH rather than the WMO-adjusted values which only go up to 100%.

a reply to: Rob48

As someone who believes that there are both chem and contrails up in the sky, I have to say this is an Interesting thread. Wasnt what I expected.

Now Im wondering..are there models that can forecast how long a contrail will persist?

originally posted by: Tucket
a reply to: Rob48

As someone who believes that there are both chem and contrails up in the sky, I have to say this is an Interesting thread. Wasnt what I expected.

Now Im wondering..are there models that can forecast how long a contrail will persist?

Not as far as I know. But I am trying to forecast "persistent contrails". Jets will often (in fact usually, at least in the UK) leave short, quickly fading vapour trails behind them, but those aren't persistent trails.

Generally speaking, if the conditions favour persistent trails, aka "chemtrails", then they will hang around and spread long after the plane has passed out of sight. They will either disperse gradually as the wind stretches them, or they will keep spreading if the humidity favours it.


As you say you believe both contrails and chemtrails exist, what distinguishes them from each other in your opinion?

originally posted by: Rob48

originally posted by: Tucket
a reply to: Rob48

As someone who believes that there are both chem and contrails up in the sky, I have to say this is an Interesting thread. Wasnt what I expected.

Now Im wondering..are there models that can forecast how long a contrail will persist?

As you say you believe both contrails and chemtrails exist, what distinguishes them from each other in your opinion?

Persistent contrails vs chemtrails? .. Not sure, although the extended persistence/ cloud cover makes me suspicious. I just figure solar radiation would do its job sooner rather than later.

a reply to: network dude

Rob, I am not as good with meteorology as you seem to be, but we currently have a hurricane passing by our coast.

Go surfing...

In my experience, just after a storm like that passes, there is at least a day and a half of real nice weather. Kind of a gift for putting up with bad weather. It's also forecasted to be nice weather after this passes.

I love the weather after a hurricane or strong tropical storm...the world seems so peaceful.

Being someone who was raised in Florida on the gulf coast I have seen a many of those days after storms.

a reply to: Rob48

I'll take some pics throughout the day and post them here. thanks very much for taking the time to look into my area.
This will be a good test for your new found skills.

originally posted by: Tucket

originally posted by: Rob48

originally posted by: Tucket
a reply to: Rob48

As someone who believes that there are both chem and contrails up in the sky, I have to say this is an Interesting thread. Wasnt what I expected.

Now Im wondering..are there models that can forecast how long a contrail will persist?

As you say you believe both contrails and chemtrails exist, what distinguishes them from each other in your opinion?

Persistent contrails vs chemtrails? .. Not sure, although the extended persistence/ cloud cover makes me suspicious. I just figure solar radiation would do its job sooner rather than later.

Nope, it's all about the saturation levels. Yesterday the air at 35000ft above my area was supersaturated with water vapour, and this was the result:



Perfectly normal contrails, but they spread out and merged into cirrus. Today, just as many planes flying over, but drier air, no trails, and clear blue skies. Simple.

originally posted by: Arktos1
I don't know if it would help, but NASA/Langley has this contrail forecasting tool here:
Contrail Formation Forecast Tool

clearly part of the Govt cover up!!

originally posted by: Rob48

originally posted by: Tucket

originally posted by: Rob48

originally posted by: Tucket
a reply to: Rob48

As someone who believes that there are both chem and contrails up in the sky, I have to say this is an Interesting thread. Wasnt what I expected.

Now Im wondering..are there models that can forecast how long a contrail will persist?

As you say you believe both contrails and chemtrails exist, what distinguishes them from each other in your opinion?

Persistent contrails vs chemtrails? .. Not sure, although the extended persistence/ cloud cover makes me suspicious. I just figure solar radiation would do its job sooner rather than later.

Nope, it's all about the saturation levels. Yesterday the air at 35000ft above my area was supersaturated with water vapour, and this was the result:

Perfectly normal contrails, but they spread out and merged into cirrus. Today, just as many planes flying over, but drier air, no trails, and clear blue skies. Simple.

It looks like cloud formation to me. Wouldnt that mean that there are other particles up there besides ice crystals helping with nucleation?

a reply to: Rob48

i got some good pics the other week