Why Do Pilots Say ‘Winds Aloft Are True’ When Forecasts Are Often Inaccurate?

True north, per Chapter 8 of the Pilot’s Handbook of Aeronautical Knowledge (PHAK), is the geographic axis that the Earth rotates about. Think of how a globe is mounted with the posts at the physical north and south poles. 

Per the PHAK: “Maps and charts are drawn using meridians of longitude that pass through the geographic poles. Directions measured from the geographic poles are called true directions.” 

The magnetic north pole where the magnetic compass points is not in the same location as the geographic north pole—the magnetic north pole 1,300 miles away. 

The difference between true and magnetic north measured in degrees is called variation, and as the name implies, the metric varies depending on where you are.

If you look at a VFR sectional, you can find variation as depicted by the dashed magenta line that stretches across the sectional. Over time—we’re talking years—variation changes—but geography (as in the “top of the world”) doesn’t.

Also, let's not forget that winds aloft are given to us in a forecast, therefore, the direction and speed are a prediction arrived at through the study and analysis of available pertinent data. Sometimes, they are going to be inaccurate.

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