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
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,
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
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...