# Could a high absolute difference between heading and course give a hint about weather conditions?

I am developing an application that tries to predict the future track of an airplane. At the moment I don't have access to weather data and I am trying to find a metric that could substitute that.

If I am not wrong, a pilot should change his heading according to wind's direction in order to maintain the airplane's course to the target airport. So If the wind benefits the airplane's movement, the absolute difference between heading and course should be zero most of the time. Is that true? If not is any another way in order to get a hint about weather conditions from heading/course information?

• Well, how about a little feedback on the answers provided? Mar 30 at 5:00

Thinking through the possibilities, if you knew the pressure conditions, and the change of those conditions as plane moves, and you knew the wind direction and speed and its changes as the plane moves, you might be able to have some kind of AI software estimate the location of the pressure centers in the airmass you're flying in, and from that calculate the pressure gradients and wind direction/velocities for some distance around the plane's location. This might be able to produce a "better than nothing" educated guess as to the wind speed and direction ahead based only on the data being received in real time.

To do this, besides an extremely powerful computer (weather forecasting agencies use multiple Cray supercomputers to predict circulation flows, but maybe you don't need that much power) you would need the normal air data inputs like ambient and dynamic pressure (indicated airspeed), and you'd need to know the airplane's true altitude and true position, which can be provided by a GPS interface.

If the software knew the precise height above the earth so it could measure ambient pressure and continuously calculate barometric pressure and measure pressure changes, and it knew the precise location, track, heading, groundspeed, and true airspeed of the airplane so it can continuously calculate wind velocity and direction (FMS systems on jets do that already), it might be able to create its own pressure pattern map of the immediate area, and from that generate a prediction of wind conditions some distance ahead.

Your question is a little confusing, but let me try to answer and perhaps help you get focused on what you actually need.

First, you are using the broad term “weather” when I think all you really care about is wind. (Winds are a subset of weather...). So the answer to your title question is yes, a large difference between heading and course indicates a strong crosswind.

As far as the first paragraph, if you have access to the internet you have access to weather data. Google “winds aloft forecast” and you will see what I mean. If you are looking for anything more specific please help us by narrowing it down.

As far as the second paragraph, yes... in a direct headwind or tailwind the course and heading will match. They are only different if there is a crosswind component that needs to be corrected for to stay on course.

Finally, without understanding the purpose or audience for your app, I will just add that every private pilot student by the time they get to cross country flight planning should have a solid understanding of the basic wind triangle. This means that they can precisely determine where they would end up if they didn’t apply a wind correction.

But that isn’t the point: Predicting the future track due to drift isn’t what is needed (by a pilot...), the correction necessary to prevent drift and determine ground speed is.

But, if you can better help us understand the purpose of this app and the intended users maybe we can provide a better answer.

A high absolute difference between heading and course can give you a hint of the weather conditions, but that hint is not very useful: it's windy and it blows from the side.

But more seriously though: I think I see what you are getting at, but to predict plane's track for meaningful distances on momentary observations of weather only is not very straightforward. Apart from certain areas in the world, weather usually is not very stable. The algrorithm or neural network doing the prediction would have to constantly update it's "knowledge" of the surroundings to keep up. And it needs a lot of data to figure out that knowledge.

A short version: my less educated guess would be, that asking such an application "check how things are now, and tell me where I will be after flying for 200nm" will yield rather useless answers.

And the longer one: Basic rules to deduce weather pattern from conditions prevailing for, say, 15 minutes should not be all too bad. As JohnK earlier mentioned, you would need multiple data sources: accurate 3d location, airspeed, temperature, heading, pressure, and then measure trends for these. Actually you'd need to know the date too... You'd get a data set that can be used to determine which weather pattern fits best to the conditions (listing the mnemonics on weather patterns would take an hour, so I'll skip that. I've always hated meteorology for that...).

The "fluid" nature of weather is what makes what you are after difficult. If you need a prediction for the track of the plane, it really is not a prediction if it updates constantly. Predicting track from a single snapshot of condition is highly unreliable for longer distances, and thus pretty much useless, at least in my opinion, and somewhat experience too.